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1. MySQL Connector/J

   ---

   MySQL provides connectivity for client applications developed in the Java programming language via a JDBC driver, which is called MySQL Connector/J.

   MySQL Connector/J is a JDBC-3.0 "Type 4" driver, which means that is is pure Java, implements version 3.0 of the JDBC specification, and communicates directly with the MySQL server using the MySQL protocol.

   This document is arranged for a beginning JDBC developer. If you are already experienced with using JDBC, you might consider starting with the section "[1]Installing Connector/J".

   While JDBC is useful by itself, we would hope that if you are not familiar with JDBC that after reading the first few sections of this manual, that you would avoid using "naked" JDBC for all but the most trivial problems and consider using one of the popular persistence frameworks such as Hibernate (http://www.hibernate.org/), Spring's JDBC templates (http://www.springframework.org/) or Ibatis SQL Maps (http://www.ibatis.com/common/sqlmaps.html) to do the majority of repetitive work and heavier lifting that is sometimes required with JDBC.

   This section is not designed to be a complete JDBC tutorial. If you need more information about using JDBC you might be interested in the following online tutorials that are more in-depth than the information presented here:

   • JDBC Basics (http://java.sun.com/docs/books/tutorial/jdbc/basics/index.html)- A tutorial from Sun covering beginner topics in JDBC
   • JDBC Short Course (http://java.sun.com/developer/onlineTraining/Database/JDBCShortCourse/i ndex.html) - A more in-depth tutorial from Sun and JGuru

1.1. Basic JDBC concepts

This section provides some general JDBC background.

1.1.1. Connecting to MySQL using the DriverManager Interface

When you are using JDBC outside of an application server, the DriverManager class manages the establishment of Connections.

The DriverManager needs to be told which JDBC drivers it should try to make Connections with. The easiest way to do this is to use Class.forName() on the class that implements the java.sql.Driver interface. With MySQL Connector/J, the name of this class is com.mysql.jdbc.Driver. With this method, you could use an external configuration file to supply the driver class name and driver parameters to use when connecting to a database.

The following section of Java code shows how you might register MySQL Connector/J from the main() method of your application: import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;

// Notice, do not import com.mysql.jdbc.* // or you will have problems!

public class LoadDriver {

public static void main(String[] args) {

        try {
            // The newInstance() call is a work around for some
            // broken Java implementations

            Class.forName("com.mysql.jdbc.Driver").newInstance();
        } catch (Exception ex) {
            // handle the error
        }

}

After the driver has been registered with the DriverManager, you can obtain a Connection instance that is connected to a particular database by calling DriverManager.getConnection():

Example 1. Obtaining a Connection From the DriverManager

This example shows how you can obtain a Connection instance from the DriverManager. There are a few different signatures for the getConnection() method. You should see the API documentation that comes with your JDK for more specific information on how to use them. import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;

... try {

Connection conn = DriverManager.getConnection("jdbc:mysql://localho st/test?user=monty&password=greatsqldb");

// Do something with the Connection

           ....
        } catch (SQLException ex) {
            // handle any errors
            System.out.println("SQLException: " + ex.getMessage());
            System.out.println("SQLState: " + ex.getSQLState());
            System.out.println("VendorError: " + ex.getErrorCode());
        }

Once a Connection is established, it can be used to create Statements and PreparedStatements, as well as retrieve metadata about the database. This is explained in the following sections.

1.1.2. Using Statements to Execute SQL

Statements allow you to execute basic SQL queries and retrieve the results through the ResultSet class which is described later.

To create a Statement instance, you call the createStatement() method on the Connection object you have retrieved via one of the DriverManager.getConnection() or DataSource.getConnection() methods described earlier.

Once you have a Statement instance, you can execute a SELECT query by calling the executeQuery(String) method with the SQL you want to use.

To update data in the database use the executeUpdate(String SQL) method. This method returns the number of rows affected by the update statement.

If you don't know ahead of time whether the SQL statement will be a SELECT or an UPDATE/INSERT, then you can use the execute(String SQL) method. This method will return true if the SQL query was a SELECT, or false if an UPDATE/INSERT/DELETE query. If the query was a SELECT query, you can retrieve the results by calling the getResultSet() method. If the query was an UPDATE/INSERT/DELETE query, you can retrieve the affected rows count by calling getUpdateCount() on the Statement instance.

Example 2. Using java.sql.Statement to Execute a SELECT Query // assume conn is an already created JDBC connection Statement stmt = null;
ResultSet rs = null;

try {

stmt = conn.createStatement();
rs = stmt.executeQuery("SELECT foo FROM bar");

// or alternatively, if you don't know ahead of time that // the query will be a SELECT...

if (stmt.execute("SELECT foo FROM bar")) {

rs = stmt.getResultSet();
}

// Now do something with the ResultSet .... } finally {

// it is a good idea to release
// resources in a finally{} block
// in reverse-order of their creation // if they are no-longer needed

if (rs != null) {

        try {
            rs.close();
        } catch (SQLException sqlEx) { // ignore }

        rs = null;

}

if (stmt != null) {

        try {
            stmt.close();
        } catch (SQLException sqlEx) { // ignore }

        stmt = null;

}
}

1.1.3. Using CallableStatements to Execute Stored Procedures

Starting with MySQL server version 5.0 when used with Connector/J 3.1.1 or newer, the java.sql.CallableStatement interface is fully implemented with the exception of the getParameterMetaData() method.

MySQL's stored procedure syntax is documented in the "Stored Procedures and Functions (http://www.mysql.com/doc/en/Stored_Procedures.html)" section of the MySQL Reference Manual.

Connector/J exposes stored procedure functionality through JDBC's CallableStatement interface.

The following example shows a stored procedure that returns the value of inOutParam incremented by 1, and the string passed in via inputParam as a ResultSet :

Example 3. Stored Procedure Example
CREATE PROCEDURE demoSp(IN inputParam VARCHAR(255), INOUT inOutParam INT) BEGIN

DECLARE z INT;
SET z = inOutParam + 1;
SET inOutParam = z;

SELECT inputParam;

SELECT CONCAT('zyxw', inputParam);
END

To use the demoSp procedure with Connector/J, follow these steps:

1. Prepare the callable statement by using Connection.prepareCall() . Notice that you have to use JDBC escape syntax, and that the parentheses surrounding the parameter placeholders are not optional: Example 4. Using Connection.prepareCall() import java.sql.CallableStatement;

...

//
// Prepare a call to the stored procedure 'demoSp' // with two parameters
//
// Notice the use of JDBC-escape syntax ({call ...}) //

CallableStatement cStmt = conn.prepareCall("{call demoSp(?, ?)}");

cStmt.setString(1, "abcdefg");

Note

       Connection.prepareCall() is an expensive method, due to the metadata
       retrieval that the driver performs to support output parameters. For
       performance reasons, you should try to minimize unnecessary calls to
       Connection.prepareCall() by reusing CallableStatement instances in your
       code.
    2. Register the output parameters (if any exist)
       To retrieve the values of output parameters (parameters specified as OUT
       or INOUT when you created the stored procedure), JDBC requires that they
       be   specified   before  statement  execution  using  the  various
       registerOutputParameter() methods in the CallableStatement interface:
       Example 5. Registering Output Parameters

import java.sql.Types;

...

//
// Connector/J supports both named and indexed // output parameters. You can register output // parameters using either method, as well // as retrieve output parameters using either // method, regardless of what method was // used to register them.
//
// The following examples show how to use // the various methods of registering // output parameters (you should of course // use only one registration per parameter). //

//
// Registers the second parameter as output //

cStmt.registerOutParameter(2);

//
// Registers the second parameter as output, and // uses the type 'INTEGER' for values returned from // getObject()
//

cStmt.registerOutParameter(2, Types.INTEGER);

//
// Registers the named parameter 'inOutParam' //

cStmt.registerOutParameter("inOutParam");

//
// Registers the named parameter 'inOutParam', and // uses the type 'INTEGER' for values returned from // getObject()
//

cStmt.registerOutParameter("inOutParam", Types.INTEGER);

...

3. Set the input parameters (if any exist)

       Input and in/out parameters are set as for PreparedStatement objects.
       However, CallableStatement also supports setting parameters by name:
       Example 6. Setting CallableStatement Input Parameters

...

//
// Set a parameter by index
//

cStmt.setString(1, "abcdefg");

//
// Alternatively, set a parameter using // the parameter name
//

cStmt.setString("inputParameter", "abcdefg");

//
// Set the 'in/out' parameter using an index //

cStmt.setInt(2, 1);

//
// Alternatively, set the 'in/out' parameter // by name
//

cStmt.setInt("inOutParam", 1);

...

4. Execute the CallableStatement , and retrieve any result sets or output

       parameters.
       While CallableStatement supports calling any of the Statement execute
       methods ( executeUpdate(), executeQuery() or execute() ), the most
       flexible method to call is execute(), as you do not need to know ahead
       of time if the stored procedure returns result sets:
       Example 7. Retrieving Results and Output Parameter Values

...

boolean hadResults = cStmt.execute();

//
// Process all returned result sets //

while (hadResults) {

ResultSet rs = cStmt.getResultSet();

// process result set

hadResults = cStmt.getMoreResults(); }

//
// Retrieve output parameters
//
// Connector/J supports both index-based and // name-based retrieval
//

int outputValue = cStmt.getInt(1); // index-based

outputValue = cStmt.getInt("inOutParam"); // name-based

...

1.1.4. Retrieving AUTO_INCREMENT Column Values

Before version 3.0 of the JDBC API, there was no standard way of retrieving key values from databases that supported 'auto increment' or identity columns. With older JDBC drivers for MySQL, you could always use a MySQLspecific method on the Statement interface, or issue the query 'SELECT LAST_INSERT_ID()' after issuing an 'INSERT' to a table that had an AUTO_INCREMENT key. Using the MySQL-specific method call isn't portable, and issuing a 'SELECT' to get the AUTO_INCREMENT key's value requires another round- trip to the database, which isn't as efficient as possible. The following code snippets demonstrate the three different ways to retrieve AUTO_INCREMENT values. First, we demonstrate the use of the new JDBC-3.0 method 'getGeneratedKeys()' which is now the preferred method to use if you need to retrieve AUTO_INCREMENT keys and have access to JDBC-3.0. The second example shows how you can retrieve the same value using a standard 'SELECT LAST_INSERT_ID()' query. The final example shows how updatable result sets can retrieve the AUTO_INCREMENT value when using the method 'insertRow()'.

Example 8. Retrieving AUTO_INCREMENT Column Values using Statement.getGeneratedKeys()
Statement stmt = null;
ResultSet rs = null;

try {

//
// Create a Statement instance that we can use for // 'normal' result sets assuming you have a // Connection 'conn' to a MySQL database already // available

stmt = conn.createStatement(java.sql.ResultSet.TYPE_FORWARD_ONLY,

java.sql.ResultSet.CONCUR_UPDATABLE);

//
// Issue the DDL queries for the table for this example //

stmt.executeUpdate("DROP TABLE IF EXISTS autoIncTutorial"); stmt.executeUpdate(

            "CREATE TABLE autoIncTutorial ("
            + "priKey INT NOT NULL AUTO_INCREMENT, "
            + "dataField VARCHAR(64), PRIMARY KEY (priKey))");

//
// Insert one row that will generate an AUTO INCREMENT // key in the 'priKey' field
//

stmt.executeUpdate(

            "INSERT INTO autoIncTutorial (dataField) "
            + "values ('Can I Get the Auto Increment Field?')",
            Statement.RETURN_GENERATED_KEYS);

//
// Example of using Statement.getGeneratedKeys() // to retrieve the value of an auto-increment // value
//

int autoIncKeyFromApi = -1;

rs = stmt.getGeneratedKeys();

if (rs.next()) {

autoIncKeyFromApi = rs.getInt(1); } else {

// throw an exception from here }

rs.close();

rs = null;

System.out.println("Key returned from getGeneratedKeys():"

+ autoIncKeyFromApi);
} finally {

if (rs != null) {

        try {
            rs.close();
        } catch (SQLException ex) {
            // ignore
        }

}

if (stmt != null) {

        try {
            stmt.close();
        } catch (SQLException ex) {
            // ignore
        }

}
}

Example 9. Retrieving AUTO_INCREMENT Column Values using 'SELECT LAST_INSERT_ID()'
Statement stmt = null;
ResultSet rs = null;

try {

//
// Create a Statement instance that we can use for // 'normal' result sets.

stmt = conn.createStatement();

//
// Issue the DDL queries for the table for this example //

stmt.executeUpdate("DROP TABLE IF EXISTS autoIncTutorial"); stmt.executeUpdate(

            "CREATE TABLE autoIncTutorial ("
            + "priKey INT NOT NULL AUTO_INCREMENT, "
            + "dataField VARCHAR(64), PRIMARY KEY (priKey))");

//
// Insert one row that will generate an AUTO INCREMENT // key in the 'priKey' field
//

stmt.executeUpdate(

            "INSERT INTO autoIncTutorial (dataField) "
            + "values ('Can I Get the Auto Increment Field?')");

//
// Use the MySQL LAST_INSERT_ID()
// function to do the same thing as getGeneratedKeys() //

int autoIncKeyFromFunc = -1;
rs = stmt.executeQuery("SELECT LAST_INSERT_ID()");

if (rs.next()) {

autoIncKeyFromFunc = rs.getInt(1); } else {

// throw an exception from here }

rs.close();

System.out.println("Key returned from " + "'SELECT LAST_INSERT_ID()': "

+ autoIncKeyFromFunc);

} finally {

if (rs != null) {

        try {
            rs.close();
        } catch (SQLException ex) {
            // ignore
        }

}

if (stmt != null) {

        try {
            stmt.close();
        } catch (SQLException ex) {
            // ignore
        }

}
}

Example 10. Retrieving AUTO_INCREMENT Column Values in Updatable ResultSets Statement stmt = null;
ResultSet rs = null;

try {

//
// Create a Statement instance that we can use for // 'normal' result sets as well as an 'updatable' // one, assuming you have a Connection 'conn' to // a MySQL database already available //

stmt = conn.createStatement(java.sql.ResultSet.TYPE_FORWARD_ONLY,

java.sql.ResultSet.CONCUR_UPDATABLE);

//
// Issue the DDL queries for the table for this example //

stmt.executeUpdate("DROP TABLE IF EXISTS autoIncTutorial"); stmt.executeUpdate(

            "CREATE TABLE autoIncTutorial ("
            + "priKey INT NOT NULL AUTO_INCREMENT, "
            + "dataField VARCHAR(64), PRIMARY KEY (priKey))");

//
// Example of retrieving an AUTO INCREMENT key // from an updatable result set
//

rs = stmt.executeQuery("SELECT priKey, dataField "

+ "FROM autoIncTutorial");

rs.moveToInsertRow();

rs.updateString("dataField", "AUTO INCREMENT here?"); rs.insertRow();

//
// the driver adds rows at the end
//

rs.last();

//
// We should now be on the row we just inserted //

int autoIncKeyFromRS = rs.getInt("priKey");

rs.close();

rs = null;

System.out.println("Key returned for inserted row: "

+ autoIncKeyFromRS);

} finally {

if (rs != null) {

        try {
            rs.close();
        } catch (SQLException ex) {
            // ignore
        }

}

if (stmt != null) {

        try {
            stmt.close();
        } catch (SQLException ex) {
            // ignore
        }

}
}

When you run the example code above, you should get the following output: Key returned from getGeneratedKeys(): 1 Key returned from 'SELECT LAST_INSERT_ID()': 1 Key returned for inserted row: 2 You should be aware, that at times, it can be tricky to use the 'SELECT LAST_INSERT_ID()' query, as that function's value is scoped to a connection. So, if some other query happens on the same connection, the value will be overwritten. On the other hand, the 'getGeneratedKeys()' method is scoped by the Statement instance, so it can be used even if other queries happen on the same connection, but not on the same Statement instance.

1.2. Installing Connector/J

Use the following instructions to install Connector/J

1.2.1. Required Software Versions

1.2.1.1. Java Versions Supported

MySQL Connector/J supports Java-2 JVMs, including JDK-1.2.x, JDK-1.3.x, JDK-1.4.x and JDK-1.5.x, and requires JDK-1.4.x or newer to compile (but not run). MySQL Connector/J does not support JDK-1.1.x or JDK-1.0.x

Because of the implementation of java.sql.Savepoint, Connector/J 3.1.0 and newer will not run on JDKs older than 1.4 unless the class verifier is turned off (-Xverify:none), as the class verifier will try to load the class definition for java.sql.Savepoint even though it is not accessed by the driver unless you actually use savepoint functionality.

Caching functionality provided by Connector/J 3.1.0 or newer is also not available on JVMs older than 1.4.x, as it relies on java.util.LinkedHashMap which was first available in JDK-1.4.0.

1.2.1.2. MySQL Server Version Guidelines

MySQL Connector/J supports all known MySQL server versions. Some features (foreign keys, updatable result sets) require more recent versions of MySQL to operate.

When connecting to MySQL server version 4.1 or newer, it is best to use MySQL Connector/J version 3.1, as it has full support for features in the newer versions of the server, including Unicode characters, views, stored procedures and server-side prepared statements.

While Connector/J version 3.0 will connect to MySQL server, version 4.1 or newer, and implements Unicode characters and the new authorization mechanism, Connector/J 3.0 will not be updated to support new features in current and future server versions.

1.2.1.3. Installing the Driver and Configuring the CLASSPATH

MySQL Connector/J is distributed as a .zip or .tar.gz archive containing the sources, the class files a class-file only "binary" .jar archive named "mysql-connector-java-[version]-bin.jar", and starting with Connector/J 3.1.8 a "debug" build of the driver in a file named "mysql-connector-java-[version]-bin-g.jar".

Starting with Connector/J 3.1.9, we don't ship the .class files "unbundled", they are only available in the JAR archives that ship with the driver.

You should not use the "debug" build of the driver unless instructed do do so when reporting a problem or bug to MySQL AB, as it is not designed to be run in production environments, and will have adverse performance impact when used. The debug binary also depends on the Aspect/J runtime library, which is located in the src/lib/aspectjrt.jar file that comes with the Connector/J distribution.

You will need to use the appropriate gui or command-line utility to un-archive the distribution (for example, WinZip for the .zip archive, and "tar" for the .tar.gz archive). Because there are potentially long filenames in the distribution, we use the GNU tar archive format. You will need to use GNU tar (or an application that understands the GNU tar archive format) to unpack the .tar.gz variant of the distribution.

Once you have extracted the distribution archive, you can install the driver by placing mysql-connector-java-[version]-bin.jar in your classpath, either by adding the FULL path to it to your CLASSPATH enviornment variable, or by directly specifying it with the commandline switch -cp when starting your JVM

If you are going to use the driver with the JDBC DriverManager, you would use "com.mysql.jdbc.Driver" as the class that implements java.sql.Driver.

Example 11. Setting the CLASSPATH Under UNIX

The following command works for 'csh' under UNIX: $ setenv CLASSPATH /path/to/mysql-connector-java-[version]-bin.jar:$CLASSPATH

The above command can be added to the appropriate startup file for the login shell to make MySQL Connector/J available to all Java applications.

If you want to use MySQL Connector/J with an application server such as Tomcat or JBoss, you will have to read your vendor's documentation for more information on how to configure third-party class libraries, as most application servers ignore the CLASSPATH environment variable. This document does contain configuration examples for some J2EE application servers in the section named "[2]Using Connector/J with J2EE and Other Java Frameworks", however the authoritative source for JDBC connection pool configuration information for your particular application server is the documentation for that application server.

If you are developing servlets and/or JSPs, and your application server is J2EE-compliant, you can put the driver's .jar file in the WEB-INF/lib subdirectory of your webapp, as this is a standard location for third party class libraries in J2EE web applications.

You can also use the MysqlDataSource or MysqlConnectionPoolDataSource classes in the com.mysql.jdbc.jdbc2.optional package, if your J2EE application server supports or requires them. The various MysqlDataSource classes support the following parameters (through standard "set" mutators):

• user
• password
• serverName (see the previous section about fail-over hosts)
• databaseName
• port

1.2.2. Upgrading from an Older Version

MySQL AB tries to keep the upgrade process as easy as possible, however as is the case with any software, sometimes changes need to be made in new versions to support new features, improve existing functionality, or comply with new standards.

This section has information about what users who are upgrading from one version of Connector/J to another (or to a new version of the MySQL server, with respect to JDBC functionality) should be aware of.

1.2.2.1. Upgrading from MySQL Connector/J 3.0 to 3.1

Connector/J 3.1 is designed to be backwards-compatible with Connector/J 3.0 as much as possible. Major changes are isolated to new functionality exposed in MySQL-4.1 and newer, which includes Unicode character sets, server-side prepared statements, SQLState codes returned in error messages by the server and various performance enhancements that can be enabled or disabled via configuration properties.

• Unicode Character Sets - See the next section, as well as the "Character Sets" section in the server manual for information on this new feature of MySQL. If you have something misconfigured, it will usually show up as an error with a message similar to 'Illegal mix of collations'.
• Server-side Prepared Statements - Connector/J 3.1 will automatically detect and use server-side prepared statements when they are available (MySQL server version 4.1.0 and newer). Starting with version 3.1.7, the driver scans SQL you are preparing via all variants of Connection.prepareStatement() to determine if it is a supported type of statement to prepare on the server side, and if it is not supported by the server, it instead prepares it as a client-side emulated prepared statement. You can disable this feature by passing 'emulateUnsupportedPstmts=false' in your JDBC URL. If your application encounters issues with server-side prepared statements, you can revert to the older client-side emulated prepared statement code that is still presently used for MySQL servers older than 4.1.0 with the following connection property: useServerPrepStmts=false
• Datetimes with all-zero components ('0000-00-00 ...') - These values can not be represented reliably in Java. Connector/J 3.0.x always converted them to NULL when being read from a ResultSet. Connector/J 3.1 throws an exception by default when these values are encountered as this is the most correct behavior according to the JDBC and SQL standards. This behavior can be modified using the ' zeroDateTimeBehavior ' configuration property. The allowable values are: 'exception' (the default), which throws a SQLException with a SQLState of 'S1009', 'convertToNull', which returns NULL instead of the date, and 'round', which rounds the date to the nearest closest value which is '0001-01-01'. Starting with Connector/J 3.1.7, ResultSet.getString() can be decoupled from this behavior via ' noDatetimeStringSync=true ' (the default value is 'false') so that you can get retrieve the unaltered all-zero value as a String. It should be noted that this also precludes using any timezone conversions, therefore the driver will not allow you to enable noDatetimeStringSync and useTimezone at the same time.
• New SQLState Codes - Connector/J 3.1 uses SQL:1999 SQLState codes returned by the MySQL server (if supported), which are different than the "legacy" X/Open state codes that Connector/J 3.0 uses. If connected to a MySQL server older than MySQL-4.1.0 (the oldest version to return SQLStates as part of the error code), the driver will use a built-in mapping. You can revert to the old mapping by using the following configuration property: useSqlStateCodes=false
• Calling ResultSet.getString() on a BLOB column will now return the address of the byte[] array that represents it, instead of a String representation of the BLOB. BLOBs have no character set, so they can't be converted to java.lang.Strings without data loss or corruption. To store strings in MySQL with LOB behavior, use one of the TEXT types, which the driver will treat as a java.sql.Clob.
• Starting with Connector/J 3.1.8 a "debug" build of the driver in a file named "mysql-connector-java-[version]-bin-g.jar" is shipped alongside the normal "binary" jar file that is named "mysql-connector-java-[version]-bin.jar". Starting with Connector/J 3.1.9, we don't ship the .class files "unbundled", they are only available in the JAR archives that ship with the driver. You should not use the "debug" build of the driver unless instructed do do so when reporting a problem or bug to MySQL AB, as it is not designed to be run in production environments, and will have adverse performance impact when used. The debug binary also depends on the Aspect/J runtime library, which is located in the src/lib/aspectjrt.jar file that comes with the Connector/J distribution.

1.2.2.2. JDBC-Specific Issues When Upgrading to MySQL Server Version 4.1 or Newer

• Using the UTF-8 Character Encoding - Prior to MySQL server version 4.1, the UTF-8 character encoding was not supported by the server, however the JDBC driver could use it, allowing storage of multiple character sets in latin1 tables on the server. Starting with MySQL-4.1, this functionality is deprecated. If you have applications that rely on this functionality, and can not upgrade them to use the official Unicode character support in MySQL server version 4.1 or newer, you should add the following property to your connection

  URL

  useOldUTF8Behavior=true

• Server-side Prepared Statements - Connector/J 3.1 will automatically detect and use server-side prepared statements when they are available (MySQL server version 4.1.0 and newer). If your application encounters issues with server-side prepared statements, you can revert to the older client-side emulated prepared statement code that is still presently used for MySQL servers older than 4.1.0 with the following connection

  property

  useServerPrepStmts=false

1.3. JDBC Reference

1.3.1. Driver/Datasource Class Names, URL Syntax and Configuration Properties for Connector/J

The name of the class that implements java.sql.Driver in MySQL Connector/J is 'com.mysql.jdbc.Driver'. The 'org.gjt.mm.mysql.Driver' class name is also usable to remain backwards-compatible with MM.MySQL. You should use this class name when registering the driver, or when otherwise configuring software to use MySQL Connector/J.

The JDBC URL format for MySQL Connector/J is as follows, with items in square brackets ([, ]) being optional: jdbc:mysql://[host][,failoverhost...][:port]/[database][?propertyName1][=proper tyValue1][&propertyName2][=propertyValue2]...

If the hostname is not specified, it defaults to '127.0.0.1'. If the port is not specified, it defaults to '3306', the default port number for MySQL servers.
jdbc:mysql://[host:port],[host:port].../[database][?propertyName1][=propertyVal ue1][&propertyName2][=propertyValue2]...

If the database is not specified, the connection will be made with no 'current' database. In this case, you will need to either call the 'setCatalog()' method on the Connection instance or fully-specify table names using the database name (i.e. 'SELECT dbname.tablename.colname FROM dbname.tablename...') in your SQL. Not specifying the database to use upon connection is generally only useful when building tools that work with multiple databases, such as GUI database managers.

MySQL Connector/J has fail-over support. This allows the driver to fail-over to any number of "slave" hosts and still perform read-only queries. Fail-over only happens when the connection is in an autoCommit(true) state, because fail-over can not happen reliably when a transaction is in progress. Most application servers and connection pools set autoCommit to 'true' at the end of every transaction/connection use.

The fail-over functionality has the following behavior:

If the URL property "autoReconnect" is false: Failover only happens at connection initialization, and failback occurs when the driver determines that the first host has become available again.

If the URL property "autoReconnect" is true: Failover happens when the driver determines that the connection has failed (before every query), and falls back to the first host when it determines that the host has become available again (after queriesBeforeRetryMaster queries have been issued).

In either case, whenever you are connected to a "failed-over" server, the connection will be set to read-only state, so queries that would modify data will have exceptions thrown (the query will never be processed by the MySQL server).

Configuration properties define how Connector/J will make a connection to a MySQL server. Unless otherwise noted, properties can be set for a DataSource object or for a Connection object.

Configuration Properties can be set in one of the following ways:

• Using the set*() methods on MySQL implementations of java.sql.DataSource (which is the preferred method when using implementations of java.sql.DataSource):

  + com.mysql.jdbc.jdbc2.optional.MysqlDataSource + com.mysql.jdbc.jdbc2.optional.MysqlConnectionPoolDataSource

• As a key/value pair in the java.util.Properties instance passed to DriverManager.getConnection() or Driver.connect()
• As a JDBC URL parameter in the URL given to java.sql.DriverManager.getConnection(),java.sql.Driver.connect()orthe MySQL implementations of javax.sql.DataSource's setURL() method.

Note

       If the mechanism you use to configure a JDBC URL is XML-based, you will
       need to use the XML character literal & to separate configuration
       parameters, as the ampersand is a reserved character for XML.

The properties are listed in the following table:

Table 1. Connection Properties
Property Name Definition Required? Default Value Since Version Connection/Authentication
user The user to connect as No all password The password to use when connecting No all socketFactory The name of the class that the driver should use for creating socket connections to the server. This class must implement the interface 'com.mysql.jdbc.SocketFactory' and have public no-args constructor. No com.mysql.jdbc.StandardSocketFactory 3.0.3 connectTimeout Timeout for socket connect (in milliseconds), with 0 being no timeout. Only works on JDK-1.4 or newer. Defaults to '0'. No 0 3.0.1 socketTimeout Timeout on network socket operations (0, the default means no timeout). No 0 3.0.1
useConfigs Load the comma-delimited list of configuration properties before parsing the URL or applying user-specified properties. These configurations are explained in the 'Configurations' of the documentation. No 3.1.5 interactiveClient Set the CLIENT_INTERACTIVE flag, which tells MySQL to timeout connections based on INTERACTIVE_TIMEOUT instead of WAIT_TIMEOUT No false 3.1.0
propertiesTransform An implementation of com.mysql.jdbc.ConnectionPropertiesTransform that the driver will use to modify URL properties passed to the driver before attempting a connection No 3.1.4
useCompression Use zlib compression when communicating with the server (true/false)? Defaults to 'false'. No false 3.0.17 High Availability and Clustering
autoReconnect Should the driver try to re-establish stale and/or dead connections? If enabled the driver will throw an exception for a queries issued on a stale or dead connection, which belong to the current transaction, but will attempt reconnect before the next query issued on the connection in a new transaction. The use of this feature is not recommended, because it has side effects related to session state and data consistency when applications don'thandle SQLExceptions properly, and is only designed to be used when you are unable to configure your application to handle SQLExceptions resulting from dead and/or stale connections properly. Alternatively, investigate setting the MySQL server variable "wait_timeout"to some high value rather than the default of 8 hours. No false 1.1
autoReconnectForPools Use a reconnection strategy appropriate for connection pools (defaults to 'false') No false 3.1.3 failOverReadOnly When failing over in autoReconnect mode, should the connection be set to 'read-only'? No true 3.0.12 reconnectAtTxEnd If autoReconnect is set to true, should the driver attempt reconnectionsat the end of every transaction? No false 3.0.10 roundRobinLoadBalance When autoReconnect is enabled, and failoverReadonly is false, should we pick hosts to connect to on a round-robin basis? No false 3.1.2
queriesBeforeRetryMaster Number of queries to issue before falling back to master when failed over (when using multi-host failover). Whichever condition is met first, 'queriesBeforeRetryMaster' or 'secondsBeforeRetryMaster' will cause an attempt to be made to reconnect to the master. Defaults to 50. No 50 3.0.2 secondsBeforeRetryMaster How long should the driver wait, when failed over, before attempting to reconnect to the master server? Whichever condition is met first, 'queriesBeforeRetryMaster' or 'secondsBeforeRetryMaster' will cause an attempt to be made to reconnect to the master. Time in seconds, defaults to 30 No 30 3.0.2
enableDeprecatedAutoreconnect Auto-reconnect functionality is deprecated starting with version 3.2, and will be removed in version 3.3. Set this property to 'true' to disable the check for the feature being configured. No false 3.2.1
Security
allowMultiQueries Allow the use of ';' to delimit multiple queries during one statement (true/false, defaults to 'false' No false 3.1.1 useSSL Use SSL when communicating with the server (true/false), defaults to 'false' No false 3.0.2
requireSSL Require SSL connection if useSSL=true? (defaults to 'false'). No false 3.1.0
allowUrlInLocalInfile Should the driver allow URLs in 'LOAD DATA LOCAL INFILE' statements? No false 3.1.4
paranoid Take measures to prevent exposure sensitive information in error messages and clear data structures holding sensitive data when possible? (defaults to 'false') No false 3.0.1 Performance Extensions
metadataCacheSize The number of queries to cacheResultSetMetadata for if cacheResultSetMetaData is set to 'true' (default 50) No 50 3.1.1 prepStmtCacheSize If prepared statement caching is enabled, how many prepared statements should be cached? No 25 3.0.10 prepStmtCacheSqlLimit If prepared statement caching is enabled, what's the largest SQL the driver will cache the parsing for? No 256 3.0.10 maintainTimeStats Should the driver maintain various internal timers to enable idle time calculations as well as more verbose error messages when the connection to the server fails? Setting this property to false removes at least two calls to System.getCurrentTimeMillis() per query. No true 3.1.9 blobSendChunkSize Chunk to use when sending BLOB/CLOBs via ServerPreparedStatements No 1048576 3.1.9 cacheCallableStmts Should the driver cache the parsing stage of CallableStatements No false 3.1.2
cachePrepStmts Should the driver cache the parsing stage of PreparedStatements of client-side prepared statements, the "check" for suitability of server-side prepared and server-side prepared statements themselves? No false 3.0.10
cacheResultSetMetadata Should the driver cache ResultSetMetaData for Statements and PreparedStatements? (Req. JDK-1.4+, true/false, default 'false') No false 3.1.1
cacheServerConfiguration Should the driver cache the results of 'SHOW VARIABLES' and 'SHOW COLLATION' on a per-URL basis? No false 3.1.5 dontTrackOpenResources The JDBC specification requires the driver to automatically track and close resources, however if your application doesn't do a good job of explicitly calling close() on statements or result sets, this can cause memory leakage. Setting this property to true relaxes this constraint, and can be more memory efficient for some applications. No false 3.1.7
dynamicCalendars Should the driver retrieve the default calendar when required, or cache it per connection/session? No false 3.1.5 elideSetAutoCommits If using MySQL-4.1 or newer, should the driver only issue 'set autocommit=n' queries when the server's state doesn't match the requested state by Connection.setAutoCommit(boolean)? No false 3.1.3 holdResultsOpenOverStatementClose Should the driver close result sets on Statement.close() as required by the JDBC specification? No false 3.1.7 locatorFetchBufferSize If 'emulateLocators' is configured to 'true', what size buffer should be used when fetching BLOB data for getBinaryInputStream? No 1048576 3.2.1
useFastIntParsing Use internal String->Integer conversion routines to avoid excessive object creation? No true 3.1.4 useLocalSessionState Should the driver refer to the internal values of autocommit and transaction isolation that are set by Connection.setAutoCommit() and Connection.setTransactionIsolation(), rather than querying the database? No false 3.1.7 useNewIO Should the driver use the java.nio.* interfaces for network communication (true/false), defaults to 'false' No false 3.1.0 useReadAheadInput Use newer, optimized non-blocking, buffered input stream when reading from the server? No true 3.1.5 Debuging/Profiling
logger The name of a class that implements 'com.mysql.jdbc.log.Log' that will be used to log messages to.(default is 'com.mysql.jdbc.log.StandardLogger', which logs to STDERR) No com.mysql.jdbc.log.StandardLogger 3.1.1 profileSQL Trace queries and their execution/fetch times to the configured logger (true/false) defaults to 'false' No false 3.1.0 reportMetricsIntervalMillis If 'gatherPerfMetrics' is enabled, how often should they be logged (in ms)? No 30000 3.1.2 maxQuerySizeToLog Controls the maximum length/size of a query that will get logged when profiling or tracing No 2048 3.1.3 packetDebugBufferSize The maximum number of packets to retain when 'enablePacketDebug' is true No 20 3.1.3 slowQueryThresholdMillis If 'logSlowQueries' is enabled, how long should a query (in ms) before it is logged as 'slow'? No 2000 3.1.2 useUsageAdvisor Should the driver issue 'usage' warnings advising proper and efficient usage of JDBC and MySQL Connector/J to the log (true/false, defaults to 'false')? No false 3.1.1 autoGenerateTestcaseScript Should the driver dump the SQL it is executing, including server-side prepared statements to STDERR? No false 3.1.9 dumpQueriesOnException Should the driver dump the contents of the query sent to the server in the message for SQLExceptions? No false 3.1.3 enablePacketDebug When enabled, a ring-buffer of 'packetDebugBufferSize' packets will be kept, and dumped when exceptions are thrown in key areas in the driver's code No false 3.1.3
explainSlowQueries If 'logSlowQueries' is enabled, should the driver automatically issue an 'EXPLAIN' on the server and send the results to the configured log at a WARN level? No false 3.1.2 logSlowQueries Should queries that take longer than 'slowQueryThresholdMillis' be logged? No false 3.1.2 traceProtocol Should trace-level network protocol be logged? No false 3.1.2 Miscellaneous
useUnicode Should the driver use Unicode character encodings when handling strings? Should only be used when the driver can't determine the character set mapping, or you are trying to 'force' the driver to use a character set that MySQL either doesn't natively support (such as UTF-8), true/false, defaults to 'true' No false 1.1g
characterEncoding If 'useUnicode' is set to true, what character encoding should the driver use when dealing with strings? (defaults is to 'autodetect') No 1.1g
characterSetResults Character set to tell the server to return results as. No 3.0.13
connectionCollation If set, tells the server to use this collation via 'set collation_connection' No 3.0.13
sessionVariables A comma-separated list of name/value pairs to be sent as SET SESSION ... to the server when the driver connects. No 3.1.8 allowNanAndInf Should the driver allow NaN or +/- INF values in PreparedStatement.setDouble()? No false 3.1.5 autoDeserialize Should the driver automatically detect and de-serialize objects stored in BLOB fields? No false 3.1.5 capitalizeTypeNames Capitalize type names in DatabaseMetaData? (usually only useful when using WebObjects, true/false, defaults to 'false') No false 2.0.7
clobberStreamingResults This will cause a 'streaming' ResultSet to be automatically closed, and any outstanding data still streaming from the server to be discarded if another query is executed before all the data has been read from the server. No false 3.0.9 continueBatchOnError Should the driver continue processing batch commands if one statement fails. The JDBC spec allows either way (defaults to 'true'). No true 3.0.3
createDatabaseIfNotExist Creates the database given in the URL if it doesn't yet exist. Assumes the configured user has permissions to create databases. No false 3.1.9
emptyStringsConvertToZero Should the driver allow conversions from empty string fields to numeric values of '0'? No true 3.1.8 emulateLocators N/A No false 3.1.0
emulateUnsupportedPstmts Should the driver detect prepared statements that are not supported by the server, and replace them with client-side emulated versions? No true 3.1.7
ignoreNonTxTables Ignore non-transactional table warning for rollback? (defaults to 'false'). No false 3.0.9 jdbcCompliantTruncation Should the driver throw java.sql.DataTruncation exceptions when data is truncated as is required by the JDBC specification when connected to a server that supports warnings(MySQL 4.1.0 and newer)? No true 3.1.2
maxRows The maximum number of rows to return (0, the default means return all rows). No -1 all versions
noDatetimeStringSync Don't ensure that ResultSet.getDatetimeType().toString().equals(ResultSet.getString()) No false 3.1.7
nullCatalogMeansCurrent When DatabaseMetadataMethods ask for a 'catalog' parameter, does the value null mean use the current catalog? (this is not JDBC-compliant, but follows legacy behavior from earlier versions of the driver) No true 3.1.8
nullNamePatternMatchesAll Should DatabaseMetaData methods that accept *pattern parameters treat null the same as '%' (this is not JDBC-compliant, however older versions of the driver accepted this departure from the specification) No true 3.1.8
pedantic Follow the JDBC spec to the letter. No false 3.0.0 relaxAutoCommit If the version of MySQL the driver connects to does not support transactions, still allow calls to commit(), rollback() and setAutoCommit() (true/false, defaults to 'false')? No false 2.0.13 retainStatementAfterResultSetClose Should the driver retain the Statement reference in a ResultSet after ResultSet.close() has been called. This is not JDBC-compliant after JDBC-4.0. No false 3.1.11 rollbackOnPooledClose Should the driver issue a rollback() when the logical connection in a pool is closed? No true 3.0.15 runningCTS13 Enables workarounds for bugs in Sun's JDBC compliance testsuite version 1.3 No false 3.1.7
serverTimezone Override detection/mapping of timezone. Used when timezone from server doesn't map to Java timezone No 3.0.2 strictFloatingPoint Used only in older versions of compliance test No false 3.0.0
strictUpdates Should the driver do strict checking (all primary keys selected) of updatable result sets (true, false, defaults to 'true')? No true 3.0.4
tinyInt1isBit Should the driver treat the datatype TINYINT(1) as the BIT type (because the server silently converts BIT -> TINYINT(1) when creating tables)? No true 3.0.16
transformedBitIsBoolean If the driver converts TINYINT(1) to a different type, should it use BOOLEAN instead of BIT for future compatibility with MySQL-5.0, as MySQL-5.0 has a BIT type? No false 3.1.9 ultraDevHack Create PreparedStatements for prepareCall() when required, because UltraDev is broken and issues a prepareCall() for all statements? (true/false, defaults to 'false') No false 2.0.3 useHostsInPrivileges Add '@hostname' to users in DatabaseMetaData.getColumn/TablePrivileges() (true/false), defaults to 'true'. No true 3.0.2
useOldUTF8Behavior Use the UTF-8 behavior the driver did when communicating with 4.0 and older servers No false 3.1.6 useOnlyServerErrorMessages Don't prepend 'standard' SQLState error messages to error messages returned by the server. No true 3.0.15 useServerPrepStmts Use server-side prepared statements if the server supports them? (defaults to 'true'). No true 3.1.0 useSqlStateCodes Use SQL Standard state codes instead of 'legacy' X/Open/SQL state codes (true/false), default is 'true' No true 3.1.3 useStreamLengthsInPrepStmts Honor stream length parameter in PreparedStatement/ResultSet.setXXXStream() method calls (true/false, defaults to 'true')? No true 3.0.2
useTimezone Convert time/date types between client and server timezones (true/false, defaults to 'false')? No false 3.0.2 useUnbufferedInput Don't use BufferedInputStream for reading data from the server No true 3.0.11
yearIsDateType Should the JDBC driver treat the MySQL type "YEAR" as a java.sql.Date, or as a SHORT? No true 3.1.9 zeroDateTimeBehavior What should happen when the driver encounters DATETIME values that are composed entirely of zeroes (used by MySQL to represent invalid dates)? Valid values are 'exception', 'round' and 'convertToNull'. No exception 3.1.4

Connector/J also supports access to MySQL via named pipes on Windows NT/2000/XP using the 'NamedPipeSocketFactory' as a plugin-socket factory via the 'socketFactory' property. If you don't use a 'namedPipePath' property, the default of '\\.\pipe\MySQL' will be used. If you use the NamedPipeSocketFactory, the hostname and port number values in the JDBC url will be ignored.

Adding the following property to your URL will enable the

NamedPipeSocketFactory

socketFactory=com.mysql.jdbc.NamedPipeSocketFactory

Named pipes only work when connecting to a MySQL server on the same physical machine as the one the JDBC driver is being used on. In simple performance tests, it appears that named pipe access is between 30%-50% faster than the standard TCP/IP access.

You can create your own socket factories by following the example code in com.mysql.jdbc.NamedPipeSocketFactory , or com.mysql.jdbc.StandardSocketFactory .

1.3.2. JDBC API Implementation Notes

MySQL Connector/J passes all of the tests in the publicly-available version of Sun's JDBC compliance testsuite. However, in many places the JDBC specification is vague about how certain functionality should be implemented, or the specification allows leeway in implementation.

This section gives details on a interface-by-interface level about how certain implementation decisions may affect how you use MySQL Connector/J.

• Blob The Blob implementation does not allow in-place modification (they are 'copies', as reported by the DatabaseMetaData.locatorsUpdateCopies() method). Because of this, you should use the corresponding PreparedStatement.setBlob() or ResultSet.updateBlob() (in the case of updatable result sets) methods to save changes back to the database. Starting with Connector/J version 3.1.0, you can emulate Blobs with locators by adding the property 'emulateLocators=true' to your JDBC URL. You must then use a column alias with the value of the column set to the actual name of the Blob column in the SELECT that you write to retrieve the Blob. The SELECT must also reference only one table, the table must have a primary key, and the SELECT must cover all columns that make up the primary key. The driver will then delay loading the actual Blob data until you retrieve the Blob and call retrieval methods (getInputStream(), getBytes(), etc) on it.
• CallableStatement Starting with Connector/J 3.1.1, stored procedures are supported when connecting to MySQL version 5.0 or newer via the CallableStatement interface. Currently, the getParameterMetaData() method of CallableStatement is not supported.
• Clob The Clob implementation does not allow in-place modification (they are 'copies', as reported by the DatabaseMetaData.locatorsUpdateCopies() method). Because of this, you should use the PreparedStatement.setClob() method to save changes back to the database. The JDBC API does not have a ResultSet.updateClob() method.
• Connection Unlike older versions of MM.MySQL the 'isClosed()' method does not "ping" the server to determine if it is alive. In accordance with the JDBC specification, it only returns true if 'closed()' has been called on the connection. If you need to determine if the connection is still valid, you should issue a simple query, such as "SELECT 1". The driver will throw an exception if the connection is no longer valid.
• DatabaseMetaData Foreign Key information (getImported/ExportedKeys() and getCrossReference()) is only available from 'InnoDB'-type tables. However, the driver uses 'SHOW CREATE TABLE' to retrieve this information, so when other table types support foreign keys, the driver will transparently support them as well.
• Driver
• PreparedStatement PreparedStatements are implemented by the driver, as MySQL does not have a prepared statement feature. Because of this, the driver does not implement getParameterMetaData() or getMetaData() as it would require the driver to have a complete SQL parser in the client. Starting with version 3.1.0 MySQL Connector/J, server-side prepared statements and 'binary-encoded' result sets are used when the server supports them. Take care when using a server-side prepared statement with "large" parameters that are set via setBinaryStream(), setAsciiStream(), setUnicodeStream(), setBlob(), or setClob(). If you want to re-execute the statement with any "large" parameter changed to a non-"large" parameter, it is necessary to call clearParameters() and set all parameters again. The reason for this is as follows:

  + The driver streams the 'large' data 'out-of-band' to the prepared statement on the server side when the parameter is set (before execution of the prepared statement). + Once that has been done, the stream used to read the data on the client side is closed (as per the JDBC spec), and can't be read from again. + If a parameter changes from "large" to non-"large", the driver must reset the server-side state of the prepared statement to allow the parameter that is being changed to take the place of the prior "large" value. This removes all of the 'large' data that has already been sent to the server, thus requiring the data to be re-sent, via the setBinaryStream(), setAsciiStream(), setUnicodeStream(), setBlob() or setClob() methods. Consequently, if you want to change the "type" of a parameter to a non-"large" one, you must call clearParameters() and set all parameters of the prepared statement again before it can be re-executed.

• ResultSet By default, ResultSets are completely retrieved and stored in memory. In most cases this is the most efficient way to operate, and due to the design of the MySQL network protocol is easier to implement. If you are working with ResultSets that have a large number of rows or large values, and can not allocate heap space in your JVM for the memory required, you can tell the driver to 'stream' the results back one row at-a-time. To enable this functionality, you need to create a Statement instance in the following manner: stmt = conn.createStatement(java.sql.ResultSet.TYPE_FORWARD_ONLY,

  java.sql.ResultSet.CONCUR_READ_ONLY); stmt.setFetchSize(Integer.MIN_VALUE);

  The combination of a forward-only, read-only result set, with a fetch size of Integer.MIN_VALUE serves as a signal to the driver to "stream" result sets row-by-row. After this any result sets created with the statement will be retrieved row-by-row. There are some caveats with this approach. You will have to read all of the rows in the result set (or close it) before you can issue any other queries on the connection, or an exception will be thrown. The earliest the locks these statements hold can be released (whether they be MyISAM table-level locks or row-level locks in some other storage engine such as InnoDB) is when the statement completes. If the statement is within scope of a transaction, then locks are released when the transaction completes (which implies that the statement needs to complete first). As with most other databases, statements are not complete until all the results pending on the statement are read or the active result set for the statement is closed. Therefore, if using "streaming" results, you should process them as quickly as possible if you want to maintain concurrent access to the tables referenced by the statement producing the result set.

• ResultSetMetaData The "isAutoIncrement()" method only works when using MySQL servers 4.0 and newer.
• Statement When using versions of the JDBC driver earlier than 3.2.1, and connected to server versions earlier than 5.0.3, the "setFetchSize()" method has no effect, other than to toggle result set streaming as described above. MySQL does not support SQL cursors, and the JDBC driver doesn't emulate them, so "setCursorName()" has no effect.

1.3.3. Java, JDBC and MySQL Types

MySQL Connector/J is flexible in the way it handles conversions between MySQL data types and Java data types.

In general, any MySQL data type can be converted to a java.lang.String, and any numerical type can be converted to any of the Java numerical types, although round-off, overflow, or loss of precision may occur.

Starting with Connector/J 3.1.0, the JDBC driver will issue warnings or throw DataTruncation exceptions as is required by the JDBC specification unless the connection was configured not to do so by using the property "jdbcCompliantTruncation" and setting it to "false".

The conversions that are always guaranteed to work are listed in the following table:

Table 2. Conversion Table
These MySQL Data Types Can always be converted to these Java types CHAR, VARCHAR, BLOB, TEXT, ENUM, and SET java.lang.String, java.io.InputStream, java.io.Reader, java.sql.Blob, java.sql.Clob FLOAT, REAL, DOUBLE PRECISION, NUMERIC, DECIMAL, TINYINT, SMALLINT, MEDIUMINT, INTEGER, BIGINT java.lang.String, java.lang.Short, java.lang.Integer, java.lang.Long, java.lang.Double, java.math.BigDecimal

Note

round-off, overflow or loss of precision may occur if you choose a Java numeric data type that has less precision or capacity than the MySQL data type you are converting to/from.
DATE, TIME, DATETIME, TIMESTAMP java.lang.String, java.sql.Date, java.sql.Timestamp

The ResultSet.getObject() method uses the following type conversions between MySQL and Java types, following the JDBC specification where appropriate:

Table 3. MySQL Types to Java Types for ResultSet.getObject() MySQL Type Name Returned as Java Class BIT(1) (new in MySQL-5.0) java.lang.Boolean BIT( > 1) (new in MySQL-5.0) byte[]
TINYINT java.lang.Boolean if the configuration property "tinyInt1isBit" is set to "true" (the default) and the storage size is "1", or java.lang.Integer if not.
BOOL , BOOLEAN See TINYINT , above as these are aliases for TINYINT(1) , currently.
SMALLINT[(M)] [UNSIGNED] java.lang.Integer (regardless if UNSIGNED or not) MEDIUMINT[(M)] [UNSIGNED] java.lang.Integer (regardless if UNSIGNED or not) INT,INTEGER[(M)] [UNSIGNED] java.lang.Integer , if UNSIGNED java.lang.Long BIGINT[(M)] [UNSIGNED] java.lang.Long , if UNSIGNED java.math.BigInteger FLOAT[(M,D)] java.lang.Float
DOUBLE[(M,B)] java.lang.Double
DECIMAL[(M[,D])] java.math.BigDecimal DATE java.sql.Date
DATETIME java.sql.Timestamp
TIMESTAMP[(M)] java.sql.Timestamp
TIME java.sql.Time
YEAR[(2|4)] java.sql.Date (with the date set two January 1st, at midnight) CHAR(M) java.lang.String (unless the character set for the column is BINARY , then byte[] is returned.
VARCHAR(M) [BINARY] java.lang.String (unless the character set for the column is BINARY , then byte[] is returned. BINARY(M) byte[]
VARBINARY(M) byte[]
TINYBLOB byte[]
TINYTEXT java.lang.String
BLOB byte[]
TEXT java.lang.String
MEDIUMBLOB byte[]
MEDIUMTEXT java.lang.String
LONGBLOB byte[]
LONGTEXT java.lang.String
ENUM('value1','value2',...) java.lang.String SET('value1','value2',...) java.lang.String

1.3.4. Using Character Sets and Unicode

All strings sent from the JDBC driver to the server are converted automatically from native Java Unicode form to the client character encoding, including all queries sent via Statement.execute(), Statement.executeUpdate(), Statement.executeQuery() as well as all PreparedStatement and CallableStatement parameters with the exclusion of parameters set using setBytes(), setBinaryStream(), setAsiiStream(), setUnicodeStream() and setBlob() .

Prior to MySQL Server 4.1, Connector/J supported a single character encoding per connection, which could either be automatically detected from the server configuration, or could be configured by the user through the useUnicode and characterEncoding properties.

Starting with MySQL Server 4.1, Connector/J supports a single character encoding between client and server, and any number of character encodings for data returned by the server to the client in ResultSets .

The character encoding between client and server is automatically detected upon connection. The encoding used by the driver is specified on the server via the configuration variable ' character_set ' for server versions older than 4.1.0 and ' character_set_server ' for server versions 4.1.0 and newer. See the "Server Character Set and Collation (http://www.mysql.com/doc/en/Charset-server.html)" section in the MySQL server manual for more information.

To override the automatically-detected encoding on the client side, use the characterEncoding property in the URL used to connect to the server.

When specifying character encodings on the client side, Java-style names should be used. The following table lists Java-style names for MySQL character sets:

Table 4. MySQL to Java Encoding Name Translations MySQL Character Set Name Java-Style Character Encoding Name

   usa7                     US-ASCII
   big5                     Big5
   gbk                      GBK
   sjis                     SJIS
   gb2312                   EUC_CN
   ujis                     EUC_JP
   euc_kr                   EUC_KR
   latin1                   ISO8859_1
   latin1_de                ISO8859_1
   german1                  ISO8859_1
   danish                   ISO8859_1
   latin2                   ISO8859_2
   czech                    ISO8859_2
   hungarian                ISO8859_2
   croat                    ISO8859_2
   greek                    ISO8859_7
   hebrew                   ISO8859_8
   latin5                   ISO8859_9
   latvian                  ISO8859_13
   latvian1                 ISO8859_13
   estonia                  ISO8859_13
   dos                      Cp437
   pclatin2                 Cp852
   cp866                    Cp866
   koi8_ru                  KOI8_R
   tis620                   TIS620
   win1250                  Cp1250
   win1250ch                Cp1250
   win1251                  Cp1251
   cp1251                   Cp1251
   win1251ukr               Cp1251
   cp1257                   Cp1257
   macroman                 MacRoman
   macce                    MacCentralEurope
   utf8                     UTF-8
   ucs2                     UnicodeBig

Warning

Do not issue the query 'set names' with Connector/J, as the driver will not detect that the character set has changed, and will continue to use the character set detected during the initial connection setup.

To allow multiple character sets to be sent from the client, the "UTF-8" encoding should be used, either by configuring "utf8" as the default server character set, or by configuring the JDBC driver to use "UTF-8" through the characterEncoding property.

1.3.5. Connecting Securely Using SSL

SSL in MySQL Connector/J encrypts all data (other than the initial handshake) between the JDBC driver and the server. The performance penalty for enabling SSL is an increase in query processing time between 35% and 50%, depending on the size of the query, and the amount of data it returns.

For SSL Support to work, you must have the following:

• A JDK that includes JSSE (Java Secure Sockets Extension), like JDK-1.4.1 or newer. SSL does not currently work with a JDK that you can add JSSE to, like JDK-1.2.x or JDK-1.3.x due to the following JSSE bug: http://developer.java.sun.com/developer/bugParade/bugs/4273544.html
• A MySQL server that supports SSL and has been compiled and configured to do so, which is MySQL-4.0.4 or later, see: http://www.mysql.com/doc/en/Secure_connections.html
• A client certificate (covered later in this section)

You will first need to import the MySQL server CA Certificate into a Java truststore. A sample MySQL server CA Certificate is located in the 'SSL' subdirectory of the MySQL source distribution. This is what SSL will use to determine if you are communicating with a secure MySQL server.

To use Java's 'keytool' to create a truststore in the current directory , and import the server's CA certificate ('cacert.pem'), you can do the following (assuming that'keytool' is in your path. It's located in the 'bin' subdirectory of your JDK or JRE):
shell> keytool -import -alias mysqlServerCACert -file cacert.pem -keystore trus tstore

Keytool will respond with the following information: Enter keystore password: *********
Owner: EMAILADDRESS=walrus@example.com, CN=Walrus, O=MySQL AB, L=Orenburg, ST=S ome
-State, C=RU
Issuer: EMAILADDRESS=walrus@example.com, CN=Walrus, O=MySQL AB, L=Orenburg, ST= Som
e-State, C=RU
Serial number: 0
Valid from: Fri Aug 02 16:55:53 CDT 2002 until: Sat Aug 02 16:55:53 CDT 2003 Certificate fingerprints:

         MD5:  61:91:A0:F2:03:07:61:7A:81:38:66:DA:19:C4:8D:AB
         SHA1: 25:77:41:05:D5:AD:99:8C:14:8C:CA:68:9C:2F:B8:89:C3:34:4D:6C

Trust this certificate? [no]: yes
Certificate was added to keystore

You will then need to generate a client certificate, so that the MySQL server knows that it is talking to a secure client: shell> keytool -genkey -keyalg rsa -alias mysqlClientCertificate -keystore key store

Keytool will prompt you for the following information, and create a keystore named 'keystore' in the current directory.

You should respond with information that is appropriate for your situation: Enter keystore password: *********
What is your first and last name?
[Unknown]: Matthews
What is the name of your organizational unit? [Unknown]: Software Development
What is the name of your organization?
[Unknown]: MySQL AB
What is the name of your City or Locality? [Unknown]: Flossmoor
What is the name of your State or Province? [Unknown]: IL
What is the two-letter country code for this unit? [Unknown]: US
Is <CN=Matthews, OU=Software Development, O=MySQL AB, L=Flossmoor, ST=IL, C=US> correct?
[no]: y

Enter key password for <mysqlClientCertificate>

(RETURN if same as keystore password):

Finally, to get JSSE to use the keystore and truststore that you have generated, you need to set the following system properties when you start your JVM, replacing 'path_to_keystore_file' with the full path to the keystore file you created, 'path_to_truststore_file' with the path to the truststore file you created, and using the appropriate password values for each property.
-Djavax.net.ssl.keyStore=path_to_keystore_file -Djavax.net.ssl.keyStorePassword=********* -Djavax.net.ssl.trustStore=path_to_truststore_file -Djavax.net.ssl.trustStorePassword=*********

You will also need to set 'useSSL' to 'true' in your connection parameters for MySQL Connector/J, either by adding 'useSSL=true' to your URL, or by setting the property 'useSSL' to 'true' in the java.util.Properties instance you pass to DriverManager.getConnection().

You can test that SSL is working by turning on JSSE debugging (as detailed below), and look for the following key events: ...
*** ClientHello, v3.1
RandomCookie: GMT: 1018531834 bytes = { 199, 148, 180, 215, 74, 12, 54, 244, 0, 168, 55, 103, 215, 64, 16, 138, 225, 190, 132, 153, 2, 217, 219, 239, 202, 1 9, 121, 78 }
Session ID: {}
Cipher Suites: { 0, 5, 0, 4, 0, 9, 0, 10, 0, 18, 0, 19, 0, 3, 0, 17 } Compression Methods: { 0 }
***
[write] MD5 and SHA1 hashes: len = 59

 0000: 01 00 00 37 03 01 3D B6   90 FA C7 94 B4 D7 4A 0C  ...7..=.......J.
 0010: 36 F4 00 A8 37 67 D7 40   10 8A E1 BE 84 99 02 D9  6...7g.@........
 0020: DB EF CA 13 79 4E 00 00   10 00 05 00 04 00 09 00  ....yN..........
 0030: 0A 00 12 00 13 00 03 00   11 01 00                 ...........

main, WRITE: SSL v3.1 Handshake, length = 59 main, READ: SSL v3.1 Handshake, length = 74 *** ServerHello, v3.1
RandomCookie: GMT: 1018577560 bytes = { 116, 50, 4, 103, 25, 100, 58, 202, 79 , 185, 178, 100, 215, 66, 254, 21, 83, 187, 190, 42, 170, 3, 132, 110, 82, 148, 160, 92 }
Session ID: {163, 227, 84, 53, 81, 127, 252, 254, 178, 179, 68, 63, 182, 158, 30, 11, 150, 79, 170, 76, 255, 92, 15, 226, 24, 17, 177, 219, 158, 177, 187, 1 43}
Cipher Suite: { 0, 5 }
Compression Method: 0
***
%% Created: [Session-1, SSL_RSA_WITH_RC4_128_SHA] ** SSL_RSA_WITH_RC4_128_SHA
[read] MD5 and SHA1 hashes: len = 74
0000: 02 00 00 46 03 01 3D B6 43 98 74 32 04 67 19 64 ...F..=.C.t2.g.d 0010: 3A CA 4F B9 B2 64 D7 42 FE 15 53 BB BE 2A AA 03 :.O..d.B..S..*.. 0020: 84 6E 52 94 A0 5C 20 A3 E3 54 35 51 7F FC FE B2 .nR..\ ..T5Q....

 0030: B3 44 3F B6 9E 1E 0B 96   4F AA 4C FF 5C 0F E2 18  .D?.....O.L.\...
 0040: 11 B1 DB 9E B1 BB 8F 00   05 00                    ..........

main, READ: SSL v3.1 Handshake, length = 1712 ...

JSSE provides debugging (to STDOUT) when you set the following system property: -Djavax.net.debug=all This will tell you what keystores and truststores are being used, as well as what is going on during the SSL handshake and certificate exchange. It will be helpful when trying to determine what is not working when trying to get an SSL connection to happen.

1.3.6. Using Master/Slave Replication with ReplicationConnection

Starting with Connector/J 3.1.7, we've made available a variant of the driver that will automatically send queries to a read/write master, or a failover or round-robin loadbalanced set of slaves based on the state of Connection.getReadOnly() .

An application signals that it wants a transaction to be read-only by calling Connection.setReadOnly(true), this "replication-aware" connection will use one of the slave connections, which are load-balanced per-vm using a round-robin scheme (a given connection is "sticky" to a slave unless that slave is removed from service). If you have a write transaction, or if you have a read that is "time-sensitive" (remember, replication in MySQL is asynchronous), set the connection to be not read-only, by calling Connection.setReadOnly(false) and the driver will ensure that further calls are sent to the "master" MySQL server. The driver takes care of propagating the current state of autocommit, isolation level, and catalog between all of the connections that it uses to accomplish this load balancing functionality.

To enable this functionality, use the " com.mysql.jdbc.ReplicationDriver " class when configuring your application server's connection pool or when creating an instance of a JDBC driver for your standalone application. Because it accepts the same URL format as the standard MySQL JDBC driver, ReplicationDriver does not currently work with java.sql.DriverManager -based connection creation unless it is the only MySQL JDBC driver registered with the DriverManager .

Here is a short, simple example of how ReplicationDriver might be used in a standalone application.
import java.sql.Connection;
import java.sql.ResultSet;
import java.util.Properties;

import com.mysql.jdbc.ReplicationDriver;

public class ReplicationDriverDemo {

public static void main(String[] args) throws Exception {

ReplicationDriver driver = new ReplicationDriver();

Properties props = new Properties();

        // We want this for failover on the slaves
        props.put("autoReconnect", "true");

        // We want to load balance between the slaves
        props.put("roundRobinLoadBalance", "true");

        props.put("user", "foo");
        props.put("password", "bar");

        //
        // Looks like a normal MySQL JDBC url, with a comma-separated list
        // of hosts, the first being the 'master', the rest being any number
        // of slaves that the driver will load balance against
        //

        Connection conn =
            driver.connect("jdbc:mysql://master,slave1,slave2,slave3/test",
                props);

        //
        // Perform read/write work on the master
        // by setting the read-only flag to "false"
        //

        conn.setReadOnly(false);
        conn.setAutoCommit(false);
        conn.createStatement().executeUpdate("UPDATE some_table ....");
        conn.commit();

        //
        // Now, do a query from a slave, the driver automatically picks one
        // from the list
        //

        conn.setReadOnly(true);

        ResultSet rs = conn.createStatement().executeQuery("SELECT a,b,c FROM s

ome_other_table");

.......
}
}

1.4. Using Connector/J with J2EE and Other Java Frameworks

This section describes how to use Connector/J in several contexts.

1.4.1. General J2EE Concepts

This section provides general background on J2EE concepts that pertain to use of Connector/J.

1.4.1.1. Understanding Connection Pooling

Connection pooling is a technique of creating and managing a pool of connections that are ready for use by any thread that needs them.

This technique of "pooling" connections is based on the fact that most applications only need a thread to have access to a JDBC connection when they are actively processing a transaction, which usually take only milliseconds to complete. When not processing a transaction, the connection would otherwise sit idle. Instead, connection pooling allows the idle connection to be used by some other thread to do useful work.

In practice, when a thread needs to do work against a MySQL or other database with JDBC, it requests a connection from the pool. When the thread is finished using the connection, it returns it to the pool, so that it may be used by any other threads that want to use it.

When the connection is "loaned out" from the pool, it is used exclusively by the thread that requested it. From a programming point of view, it is the same as if your thread called DriverManager.getConnection() every time it needed a JDBC connection, however with connection pooling, your thread may end up using either a new, or already-existing connection.

Connection pooling can greatly increase the performance of your Java application, while reducing overall resource usage. The main benefits to connection pooling are:

• Reduced connection creation time While this is not usually an issue with the quick connection setup that MySQL offers compared to other databases, creating new JDBC connections still incurs networking and JDBC driver overhead that will be avoided if connections are "recycled."
• Simplified programming model When using connection pooling, each individual thread can act as though it has created its own JDBC connection, allowing you to use straight-forward JDBC programming techniques.
• Controlled resource usage If you don't use connection pooling, and instead create a new connection every time a thread needs one, your application's resource usage can be quite wasteful and lead to unpredictable behavior under load.

Remember that each connection to MySQL has overhead (memory, CPU, context switches, etc) on both the client and server side. Every connection limits how many resources there are available to your application as well as the MySQL server. Many of these resources will be used whether or not the connection is actually doing any useful work!

Connection pools can be tuned to maximize performance, while keeping resource utilization below the point where your application will start to fail rather than just run slower.

Luckily, Sun has standardized the concept of connection pooling in JDBC through the JDBC-2.0 "Optional" interfaces, and all major application servers have implementations of these APIs that work fine with MySQL Connector/J.

Generally, you configure a connection pool in your application server configuration files, and access it via the Java Naming and Directory Interface (JNDI). The following code shows how you might use a connection pool from an application deployed in a J2EE application server:

Example 12. Using a Connection Pool with a J2EE Application Server import java.sql.Connection;
import java.sql.SQLException;
import java.sql.Statement;

import javax.naming.InitialContext;
import javax.sql.DataSource;

public class MyServletJspOrEjb {

public void doSomething() throws Exception {

        /*
         * Create a JNDI Initial context to be able to
         *  lookup  the DataSource
         *
         * In production-level code, this should be cached as
         * an instance or static variable, as it can
         * be quite expensive to create a JNDI context.
         *
         * Note: This code only works when you are using servlets
         * or EJBs in a J2EE application server. If you are
         * using connection pooling in standalone Java code, you
         * will have to create/configure datasources using whatever
         * mechanisms your particular connection pooling library
         * provides.
         */

        InitialContext ctx = new InitialContext();

         /*
          * Lookup the DataSource, which will be backed by a pool
          * that the application server provides. DataSource instances
          * are also a good candidate for caching as an instance
          * variable, as JNDI lookups can be expensive as well.
          */

        DataSource ds = (DataSource)ctx.lookup("java:comp/env/jdbc/MySQLDB");

        /*
         * The following code is what would actually be in your
         * Servlet, JSP or EJB 'service' method...where you need
         * to work with a JDBC connection.
         */

        Connection conn = null;
        Statement stmt = null;

        try {
            conn = ds.getConnection();

            /*
             * Now, use normal JDBC programming to work with
             * MySQL, making sure to close each resource when you're
             * finished with it, which allows the connection pool
             * resources to be recovered as quickly as possible
             */

            stmt = conn.createStatement();
            stmt.execute("SOME SQL QUERY");

            stmt.close();
            stmt = null;

            conn.close();
            conn = null;
        } finally {
            /*
             * close any jdbc instances here that weren't
             * explicitly closed during normal code path, so
             * that we don't 'leak' resources...
             */

            if (stmt != null) {
                try {
                    stmt.close();
                } catch (sqlexception sqlex) {
                    // ignore -- as we can't do anything about it here
                }

                stmt = null;
            }

            if (conn != null) {
                try {
                    conn.close();
                } catch (sqlexception sqlex) {
                    // ignore -- as we can't do anything about it here
                }

                conn = null;
            }
        }

}
}

As shown in the example above, after obtaining the JNDI InitialContext, and looking up the DataSource, the rest of the code should look familiar to anyone who has done JDBC programming in the past.

The most important thing to remember when using connection pooling is to make sure that no matter what happens in your code (exceptions, flow-of-control, etc), connections, and anything created by them (statements, result sets, etc) are closed, so that they may be re-used, otherwise they will be "stranded," which in the best case means that the MySQL server resources they represent (buffers, locks, sockets, etc) may be tied up for some time, or worst case, may be tied up forever.

What's the Best Size for my Connection Pool?

As with all other configuration rules-of-thumb, the answer is "It depends." While the optimal size depends on anticipated load and average database transaction time, the optimum connection pool size is smaller than you might expect. If you take Sun's Java Petstore blueprint application for example, a connection pool of 15-20 connections can serve a relatively moderate load (600 concurrent users) using MySQL and Tomcat with response times that are acceptable.

To correctly size a connection pool for your application, you should create load test scripts with tools such as Apache JMeter or The Grinder, and load test your application.

An easy way to determine a starting point is to configure your connection pool's maximum number of connections to be "unbounded," run a load test, and measure the largest amount of concurrently used connections. You can then work backwards from there to determine what values of minimum and maximum pooled connections give the best performance for your particular application.

1.4.2. Using Connector/J with Tomcat

The following instructions are based on the instructions for Tomcat-5.x, available at
http://jakarta.apache.org/tomcat/tomcat-5.0-doc/jndi-datasource-examples-how to.html which is current at the time this document was written.

First, install the .jar file that comes with Connector/J in $CATALINA_HOME/common/lib so that it is available to all applications installed in the container.

Next, Configure the JNDI DataSource by adding a declaration resource to $CATALINA_HOME/conf/server.xml in the context that defines your web

application

<Context ....>

...

<Resource name="jdbc/MySQLDB"

               auth="Container"
               type="javax.sql.DataSource"/>

<!-- The name you used above, must match exactly here!

       The connection pool will be bound into JNDI with the name
       "java:/comp/env/jdbc/MySQLDB"

-->

<ResourceParams name="jdbc/MySQLDB">
<parameter>

      <name>factory</name>
      <value>org.apache.commons.dbcp.BasicDataSourceFactory</value>

</parameter>

<!-- Don't set this any higher than max_connections on your

         MySQL server, usually this should be a 10 or a few 10's
         of connections, not hundreds or thousands -->

<parameter>

      <name>maxActive</name>
      <value>10</value>

</parameter>

<!-- You don't want to many idle connections hanging around

         if you can avoid it, only enough to soak up a spike in
         the load -->

<parameter>

      <name>maxIdle</name>
      <value>5</value>

</parameter>

<!-- Don't use autoReconnect=true, it's going away eventually

         and it's a crutch for older connection pools that couldn't
         test connections. You need to decide if your application is
         supposed to deal with SQLExceptions (hint, it should), and
         how much of a performance penalty you're willing to pay
         to ensure 'freshness' of the connection -->

<parameter>

      <name>validationQuery</name>
      <value>SELECT 1</value>

</parameter>

<!-- The most conservative approach is to test connections

        before they're given to your application. For most applications
        this is okay, the query used above is very small and takes
        no real server resources to process, other than the time used
        to traverse the network.

        If you have a high-load application you'll need to rely on
        something else. -->

<parameter>

      <name>testOnBorrow</name>
      <value>true</value>

</parameter>

<!-- Otherwise, or in addition to testOnBorrow, you can test

while connections are sitting idle -->

<parameter>

      <name>testWhileIdle</name>
      <value>true</value>

</parameter>

<!-- You have to set this value, otherwise even though

         you've asked connections to be tested while idle,
         the idle evicter thread will never run -->

<parameter>

      <name>timeBetweenEvictionRunsMillis</name>
      <value>10000</value>

</parameter>

<!-- Don't allow connections to hang out idle too long,

         never longer than what wait_timeout is set to on the
         server...A few minutes or even fraction of a minute
         is sometimes okay here, it depends on your application
         and how much spikey load it will see -->

<parameter>

      <name>minEvictableIdleTimeMillis</name>
      <value>60000</value>

</parameter>

<!-- Username and password used when connecting to MySQL -->

<parameter>

     <name>username</name>
     <value>someuser</value>

</parameter>

<parameter>

     <name>password</name>
     <value>somepass</value>

</parameter>

<!-- Class name for the Connector/J driver -->

<parameter>

       <name>driverClassName</name>
       <value>com.mysql.jdbc.Driver</value>

</parameter>

<!-- The JDBC connection url for connecting to MySQL, notice

         that if you want to pass any other MySQL-specific parameters
         you should pass them here in the URL, setting them using the
         parameter tags above will have no effect, you will also
         need to use & to separate parameter values as the
         ampersand is a reserved character in XML -->

<parameter>

      <name>url</name>
      <value>jdbc:mysql://localhost:3306/test</value>

</parameter>

</ResourceParams>
</Context>

In general, you should follow the installation instructions that come with your version of Tomcat, as the way you configure datasources in Tomcat changes from time-to-time, and unfortunately if you use the wrong syntax in your XML file, you will most likely end up with an exception similar to the

following

Error: java.sql.SQLException:Cannot load JDBC driver class 'null ' SQL state: null

1.4.3. Using Connector/J with JBoss

These instructions cover JBoss-4.x. To make the JDBC driver classes available to the application server, copy the .jar file that comes with Connector/J to the lib directory for your server configuration (which is usually called "default"). Then, in the same configuration directory, in the subdirectory named "deploy", create a datasource configuration file that ends with "-ds.xml", which tells JBoss to deploy this file as a JDBC Datasource. The file should have the following contents: <datasources>

<local-tx-datasource>

        <!-- This connection pool will be bound into JNDI with the name
             "java:/MySQLDB" -->

        <jndi-name>MySQLDB</jndi-name>
        <connection-url>jdbc:mysql://localhost:3306/dbname</connection-url>
        <driver-class>com.mysql.jdbc.Driver</driver-class>
        <user-name>user</user-name>
        <password>pass</password>

        <min-pool-size>5</min-pool-size>

        <!-- Don't set this any higher than max_connections on your
         MySQL server, usually this should be a 10 or a few 10's
         of connections, not hundreds or thousands -->

        <max-pool-size>20</max-pool-size>

        <!-- Don't allow connections to hang out idle too long,
         never longer than what wait_timeout is set to on the
         server...A few minutes is usually okay here,
         it depends on your application
         and how much spikey load it will see -->

        <idle-timeout-minutes>5</idle-timeout-minutes>

        <!-- If you're using Connector/J 3.1.8 or newer, you can use
             our implementation of these to increase the robustness
             of the connection pool. -->

        <exception-sorter-class-name>com.mysql.jdbc.integration.jboss.ExtendedM
ysqlExceptionSorter</exception-sorter-class-name>
        <valid-connection-checker-class-name>com.mysql.jdbc.integration.jboss.M

ysqlValidConnectionChecker</valid-connection-checker-class-name>

</local-tx-datasource>
</datasources>

1.5. Diagnosing Connector/J Problems

This section describes how to solve problems that you may encounter when using Connector/J.

1.5.1. Common Problems and Solutions

There are a few issues that seem to be commonly encountered often by users of MySQL Connector/J. This section deals with their symptoms, and their resolutions. If you have further issues, see the "SUPPORT" section.

1.5.1.1:

Question

When I try to connect to the database with MySQL Connector/J, I get the following exception:
SQLException: Server configuration denies access to data source SQLState: 08001
VendorError: 0

What's going on? I can connect just fine with the MySQL command-line client.

Answer

MySQL Connector/J must use TCP/IP sockets to connect to MySQL, as Java does not support Unix Domain Sockets. Therefore, when MySQL Connector/J connects to MySQL, the security manager in MySQL server will use its grant tables to determine whether or not the connection should be allowed.

You must add grants to allow this to happen. The following is an example of how to do this (but not the most secure).

From the mysql command-line client, logged in as a user that can grant privileges, issue the following command: GRANT ALL PRIVILEGES ON [dbname].* to

                '[user]'@'[hostname]' identified by
                '[password]'

replacing [dbname] with the name of your database, [user] with the user name, [hostname] with the host that MySQL Connector/J will be connecting from, and [password] with the password you want to use. Be aware that RedHat Linux is broken with respect to the hostname portion for the case when you are connecting from localhost. You need to use "localhost.localdomain" for the [hostname] value in this case. Follow this by issuing the "FLUSH PRIVILEGES" command.

Note

Testing your connectivity with the "mysql" command-line client will not work unless you add the "--host" flag, and use something other than "localhost" for the host. The "mysql" command-line client will use Unix domain sockets if you use the special hostname "localhost". If you are testing connectivity to "localhost", use "127.0.0.1" as the hostname instead.

Warning

If you don't understand what the 'GRANT' command does, or how it works, you should read and understand the 'General Security Issues and the MySQL Access Privilege System' (http://www.mysql.com/doc/en/Privilege_system.html) section of the MySQL manual before attempting to change privileges.

Changing privileges and permissions improperly in MySQL can potentially cause your server installation to not have optimal security properties.

1.5.1.2:

Question

My application throws a SQLException 'No Suitable Driver'. Why is this happening?

Answer

One of two things are happening. Either the driver is not in your CLASSPATH (see the "INSTALLATION" section above), or your URL format is incorrect (see "Developing Applications with MySQL Connector/J").

1.5.1.3:

Question

I'm trying to use MySQL Connector/J in an applet or application and I get an exception similar to:
SQLException: Cannot connect to MySQL server on host:3306. Is there a MySQL server running on the machine/port you are trying to connect to?

(java.security.AccessControlException)
SQLState: 08S01
VendorError: 0

Answer

Either you're running an Applet, your MySQL server has been installed with the "--skip-networking" option set, or your MySQL server has a firewall sitting in front of it.

Applets can only make network connections back to the machine that runs the web server that served the .class files for the applet. This means that MySQL must run on the same machine (or you must have some sort of port re-direction) for this to work. This also means that you will not be able to test applets from your local file system, you must always deploy them to a web server.

MySQL Connector/J can only communicate with MySQL using TCP/IP, as Java does not support Unix domain sockets. TCP/IP communication with MySQL might be affected if MySQL was started with the "--skip-networking" flag, or if it is firewalled.

If MySQL has been started with the "--skip-networking" option set (the Debian Linux package of MySQL server does this for example), you need to comment it out in the file /etc/mysql/my.cnf or /etc/my.cnf. Of course your my.cnf file might also exist in the "data" directory of your MySQL server, or anywhere else (depending on how MySQL was compiled for your system). Binaries created by MySQL AB always look in /etc/my.cnf and [datadir]/my.cnf. If your MySQL server has been firewalled, you will need to have the firewall configured to allow TCP/IP connections from the host where your Java code is running to the MySQL server on the port that MySQL is listening to (by default, 3306).

1.5.1.4:

Question

I have a servlet/application that works fine for a day, and then stops working overnight

Answer

MySQL closes connections after 8 hours of inactivity. You either need to use a connection pool that handles stale connections or use the "autoReconnect" parameter (see "Developing Applications with MySQL Connector/J").

Also, you should be catching SQLExceptions in your application and dealing with them, rather than propagating them all the way until your application exits, this is just good programming practice. MySQL Connector/J will set the SQLState (see java.sql.SQLException.getSQLState() in your APIDOCS) to "08S01" when it encounters network-connectivity issues during the processing of a query. Your application code should then attempt to re-connect to MySQL at this point.

The following (simplistic) example shows what code that can handle these exceptions might look like:

Example 13. Example of transaction with retry logic public void doBusinessOp() throws SQLException {

        Connection conn = null;
        Statement stmt = null;
        ResultSet rs = null;

        //
        // How many times do you want to retry the transaction
        // (or at least getting a connection)?
        //
        int retryCount = 5;

        boolean transactionCompleted = false;

        do {
            try {
                conn = getConnection(); // assume getting this from a
                                        // javax.sql.DataSource, or the
                                        // java.sql.DriverManager

                conn.setAutoCommit(false);

                //
                // Okay, at this point, the 'retry-ability' of the
                // transaction really depends on your application logic,
                // whether or not you're using autocommit (in this case
                // not), and whether you're using transacational storage
                // engines
                //
                // For this example, we'll assume that it's not safe
                // to retry the entire transaction, so we set retry count
                // to 0 at this point
                //
                // If you were using exclusively transaction-safe tables,
                // or your application could recover from a connection going
                // bad in the middle of an operation, then you would not
                // touch 'retryCount' here, and just let the loop repeat
                // until retryCount == 0.
                //
                retryCount = 0;

                stmt = conn.createStatement();

                String query = "SELECT foo FROM bar ORDER BY baz";

                rs = stmt.executeQuery(query);

                while (rs.next()) {
                }

                rs.close();
                rs = null;

                stmt.close();
                stmt = null;

                conn.commit();
                conn.close();
                conn = null;

                transactionCompleted = true;
            } catch (SQLException sqlEx) {

                //
                // The two SQL states that are 'retry-able' are 08S01
                // for a communications error, and 41000 for deadlock.
                //
                // Only retry if the error was due to a stale connection,
                // communications problem or deadlock
                //

                String sqlState = sqlEx.getSQLState();

                if ("08S01".equals(sqlState) || "41000".equals(sqlState)) {
                    retryCount--;
                } else {
                    retryCount = 0;
                }
            } finally {
                if (rs != null) {
                    try {
                        rs.close();
                    } catch (SQLException sqlEx) {
                        // You'd probably want to log this . . .
                    }
                }

                if (stmt != null) {
                    try {
                        stmt.close();
                    } catch (SQLException sqlEx) {
                        // You'd probably want to log this as well . . .
                    }
                }

                if (conn != null) {
                    try {
                        //
                        // If we got here, and conn is not null, the
                        // transaction should be rolled back, as not
                        // all work has been done

                        try {
                            conn.rollback();
                        } finally {
                            conn.close();
                        }
                    } catch (SQLException sqlEx) {
                        //
                        // If we got an exception here, something
                        // pretty serious is going on, so we better
                        // pass it up the stack, rather than just
                        // logging it. . .

                        throw sqlEx;
                    }
                }
            }
        } while (!transactionCompleted && (retryCount > 0));

}

1.5.1.5:

Question

I'm trying to use JDBC-2.0 updatable result sets, and I get an exception saying my result set is not updatable.

Answer

Because MySQL does not have row identifiers, MySQL Connector/J can only update result sets that have come from queries on tables that have at least one primary key, the query must select all of the primary key(s) and the query can only span one table (i.e. no joins). This is outlined in the JDBC specification.

1.5.2. How to Report Bugs or Problems

The normal place to report bugs is http://bugs.mysql.com/, which is the address for our bugs database. This database is public, and can be browsed and searched by anyone. If you log in to the system, you will also be able to enter new reports.

If you have found a sensitive security bug in MySQL, you can send email to security@mysql.com (mailto:security@mysql.com).

Writing a good bug report takes patience, but doing it right the first time saves time both for us and for yourself. A good bug report, containing a full test case for the bug, makes it very likely that we will fix the bug in the next release.

This section will help you write your report correctly so that you don't waste your time doing things that may not help us much or at all.

If you have a repeatable bug report, please report it to the bugs database at http://bugs.mysql.com/ (???).

Any bug that we are able to repeat has a high chance of being fixed in the next MySQL release.

To report other problems, you can use one of the MySQL mailing lists.

Remember that it is possible for us to respond to a message containing too much information, but not to one containing too little. People often omit facts because they think they know the cause of a problem and assume that some details don't matter.

A good principle is this: If you are in doubt about stating something, state it. It is faster and less troublesome to write a couple more lines in your report than to wait longer for the answer if we must ask you to provide information that was missing from the initial report.

The most common errors made in bug reports are (a) not including the version number of Connector/J or MySQL used, and (b) not fully describing the platform on which Connector/J is installed (including the JVM version, and the platform type and version number that MySQL itself is installed on).

This is highly relevant information, and in 99 cases out of 100, the bug report is useless without it. Very often we get questions like, ``Why doesn't this work for me?'' Then we find that the feature requested wasn't implemented in that MySQL version, or that a bug described in a report has already been fixed in newer MySQL versions.

Sometimes the error is platform-dependent; in such cases, it is next to impossible for us to fix anything without knowing the operating system and the version number of the platform.

If at all possible, you should create a repeatable, stanalone testcase that doesn't involve any third-party classes.

To streamline this process, we ship a base class for testcases with Connector/J, named ' com.mysql.jdbc.util.BaseBugReport '. To create a testcase for Connector/J using this class, create your own class that inherits from com.mysql.jdbc.util.BaseBugReport and override the methods setUp(), tearDown() and runTest ().

In the setUp() method, create code that creates your tables, and populates them with any data needed to demonstrate the bug.

In the runTest () method, create code that demonstrates the bug using the tables and data you created in the 'setUp' method.

In the tearDown() method, drop any tables you created in the setUp() method.

In any of the above three methods, you should use one of the variants of the getConnection () method to create a JDBC connection to MySQL:

• getConnection() - Provides a connection to the JDBC URL specified in getUrl(). If a connection already exists, that connection is returned, otherwise a new connection is created.
• getNewConnection() - Use this if you need to get a new connection for your bug report (i.e. there's more than one connection involved).
• getConnection(String url) - Returns a connection using the given URL.
• getConnection(String url, Properties props) - Returns a connection using the given URL and properties.

If you need to use a JDBC URL that is different than 'jdbc:mysql:///test', then override the method getUrl() as well.

Use the assertTrue(boolean expression) and assertTrue(String failureMessage, boolean expression) methods to create conditions that must be met in your testcase demonstrating the behavior you are expecting (vs. the behavior you are observing, which is why you are most likely filing a bug report).

Finally, create a main () method that creates a new instance of your testcase, and calls the run method:
public static void main(String[] args) throws Exception {

new MyBugReport().run();
}

Once you have finished your testcase, and have verified that it demonstrates the bug you are reporting, upload it with your bug report to http://bugs.mysql.com/.

1.6. Changelog

# Changelog
# $Id: CHANGES,v 1.38.4.206 2005/05/12 15:25:54 mmatthews Exp $

05-17-05 - Version 3.2.1-alpha

• Autoreconnect functionality (i.e. autoReconnect=true) is now deprecated. An exception will be thrown if you try and use it, use 'enableDeprecatedAutoreconnect=true' to still use autoReconnect. However this feature will be removed in Connector/J 3.3, see the manual for solutions that don't require autoReconnect to be used.
• Driver now checks if server variable 'init_connect' is set, and if so checks autocommit setting, and applies it.
• If connected to server > 5.0.x, and Statement.setFetchSize( > 0), the driver will try and use server prepared statements and fetch statements using result set 'cursors'.
• ServerPreparedStatements now correctly 'stream' BLOB/CLOB data to the server. You can configure the threshold chunk size using the JDBC URL property 'blobSendChunkSize' (the default is one megabyte).
• Support sql mode NO_BACKSLASH_ESCAPES with non-server-side prepared statements.

12-23-04 - Version 3.2.0-alpha

• Fixed incorrect return values from DatabaseMetaData.supportsCatalogIn*().
• Support for 'cursor' based result sets when using ServerPreparedStatement s

  and MySQL 5.0 or newer. Result set needs to be forward-only, and a non-ze ro

  fetch size for this feature to be enabled.

• Refactoring of where logic for prepared statement, server-prepared statement lives.

10-07-05 - Version 3.1.11-stable

• Fixed BUG#11629 (http://bugs.mysql.com/11629) - Spurious "!" on console w hen character

  encoding is "utf8".

• Fixed statements generated for testcases missing ";" for "plain" statements.
• Fixed BUG#11663 (http://bugs.mysql.com/11663) - Incorrect generation of t estcase scripts

  for server-side prepared statements.

• Fixed regression caused by fix for BUG#11552 (http://bugs.mysql.com/11552 ) that caused driver

  to return incorrect values for unsigned integers when those integers where within the range of the positive signed type.

• Moved source code to svn repo.
• Fixed BUG#11797 (http://bugs.mysql.com/11797) - Escape tokenizer doesn't respect stacked single quotes

  for escapes.

• GEOMETRY type not recognized when using server-side prepared statements.
• Fixed BUG#11879 (http://bugs.mysql.com/11879) -- ReplicationConnection wo n't switch to slave, throws

  "Catalog can't be null" exception.

• Fixed BUG#12218 (http://bugs.mysql.com/12218), properties shared between master and slave with

  replication connection.

• Fixed BUG#10630 (http://bugs.mysql.com/10630), Statement.getWarnings() fa ils with NPE if statement

  has been closed.

• Only get char[] from SQL in PreparedStatement.ParseInfo() when needed.
• Fixed BUG#12104 (http://bugs.mysql.com/12104) - Geometry types not handle d with server-side prepared

  statements.

• Fixed BUG#11614 (http://bugs.mysql.com/11614) - StringUtils.getBytes() do esn't work when using

  multibyte character encodings and a length in characters is specified.

• Fixed BUG#11798 (http://bugs.mysql.com/11798) - Pstmt.setObject(...., Typ es.BOOLEAN) throws exception.
• Fixed BUG#11976 (http://bugs.mysql.com/11976) - maxPerformance.properties mis-spells

  "elideSetAutoCommits".

• Fixed BUG#11575 (http://bugs.mysql.com/11575) -- DBMD.storesLower/Mixed/U pperIdentifiers()

  reports incorrect values for servers deployed on Windows.

• Fixed BUG#11190 (http://bugs.mysql.com/11190) - ResultSet.moveToCurrentRo w() fails to work when

  preceeded by a call to ResultSet.moveToInsertRow().

• Fixed BUG#11115 (http://bugs.mysql.com/11115), VARBINARY data corrupted w hen using server-side

  prepared statements and .setBytes().

• Fixed BUG#12229 (http://bugs.mysql.com/12229) - explainSlowQueries hangs with server-side

  prepared statements.

• Fixed BUG#11498 (http://bugs.mysql.com/11498) - Escape processor didn't h onor strings demarcated

  with double quotes.

• Lifted restriction of changing streaming parameters with server-side prepared statements. As long as all streaming parameters were set before execution, .clearParameters() does not have to be called. (due to limitation of client/server protocol, prepared statements can not reset individual stream data on the server side).
• Reworked Field class, *Buffer, and MysqlIO to be aware of field lengths > Integer.MAX_VALUE.
• Updated DBMD.supportsCorrelatedQueries() to return true for versions > 4.1, supportsGroupByUnrelated() to return true and getResultSetHoldability() to return HOLD_CURSORS_OVER_COMMIT.
• Fixed BUG#12541 (http://bugs.mysql.com/12541) - Handling of catalog argum ent in

  DatabaseMetaData.getIndexInfo(), which also means changes to the followin g

  methods in DatabaseMetaData:

• getBestRowIdentifier()
• getColumns()
• getCrossReference()
• getExportedKeys()
• getImportedKeys()
• getIndexInfo()
• getPrimaryKeys()
• getProcedures() (and thus indirectly getProcedureColumns())
• getTables()

  The "catalog" argument in all of these methods now behaves in the followi ng

  way

  • Specifying NULL means that catalog will not be used to filter the results (thus all databases will be searched), unless you've set "nullCatalogMeansCurrent=true" in your JDBC URL properties.
  • Specifying "" means "current" catalog, even though this isn't quite JDBC spec compliant, it's there for legacy users.
  • Specifying a catalog works as stated in the API docs.
  • Made Connection.clientPrepare() available from "wrapped" connections in the jdbc2.optional package (connections built by ConnectionPoolDataSource instances).

• Added Connection.isMasterConnection() for clients to be able to determine if a multi-host master/slave connection is connected to the first host in the list.
• Fixed BUG#12753 (http://bugs.mysql.com/12753) - Tokenizer for "=" in URL properties was causing

  sessionVariables=.... to be parameterized incorrectly.

• Fixed BUG#11781 (http://bugs.mysql.com/11781), foreign key information th at is quoted is

  parsed incorrectly when DatabaseMetaData methods use that information.

• The "sendBlobChunkSize" property is now clamped to "max_allowed_packet" with consideration of stream buffer size and packet headers to avoid PacketTooBigExceptions when "max_allowed_packet" is similar in size to the default "sendBlobChunkSize" which is 1M.
• CallableStatement.clearParameters() now clears resources associated with INOUT/OUTPUT parameters as well as INPUT parameters.
• Fixed BUG#12417 (http://bugs.mysql.com/12417) - Connection.prepareCall() is database name

  case-sensitive (on Windows systems).

• Fixed BUG#12752 (http://bugs.mysql.com/12752) - Cp1251 incorrectly mapped to win1251 for

  servers newer than 4.0.x.

• Fixed BUG#12970 (http://bugs.mysql.com/12970) - java.sql.Types.OTHER retu rned for

  BINARY and VARBINARY columns when using DatabaseMetaData.getColumns().

• ServerPreparedStatement.getBinding() now checks if the statement is closed before attempting to reference the list of parameter bindings, to avoid throwing a NullPointerException.
• Fixed BUG#13277 (http://bugs.mysql.com/13277) - ResultSetMetaData from Statement.getGeneratedKeys() caused NullPointerExceptions to be thrown whenever a method that required a connection reference was called.
• Backport of Field class, ResultSetMetaData.getColumnClassName(), and ResultSet.getObject(int) changes from 5.0 branch to fix behavior surrounding VARCHAR BINARY/VARBINARY and related types.
• Fixed NullPointerException when converting "catalog" parameter in many DatabaseMetaDataMethods to byte[]s (for the result set) when the parameter is null. ("null" isn't technically allowed by the JDBC specification, but we've historically allowed it).
• Backport of VAR[BINARY|CHAR] [BINARY] types detection from 5.0 branch.
• Read response in MysqlIO.sendFileToServer(), even if the local file can't be opened, otherwise next query issued will fail, because it's reading the response to the empty LOAD DATA INFILE packet sent to the server.
• Workaround for BUG#13374 (http://bugs.mysql.com/13374) - ResultSet.getSta tement()

  on closed result set returns NULL (as per JDBC 4.0 spec, but not backwards-compatible). Set the connection property "retainStatementAfterResultSetClose" to "true" to be able to retrieve a ResultSet's statement after the ResultSet has been closed via .getStatement() (the default is "false", to be JDBC-compliant and to reduce the chance that code using JDBC leaks Statement instances).

• Fixed BUG#13453 (http://bugs.mysql.com/13453) - URL configuration paramet ers don't allow

  '&' or '=' in their values. The JDBC driver now parses configuration parameters as if they are encoded using the application/x-www-form-urlencoded format as specified by java.net.URLDecoder - http://java.sun.com/j2s