How to Prevent JDBC MySQL Connection Pool Exhaustion in Java Web Applications?

JDBC MySQL Connection Pooling: Best Practices to Avoid Exhausted Connections

When using connection pooling in Java web applications, it's crucial to avoid exhausting the pool. This can occur if connections are not closed properly, leading to the application crashing due to a lack of available connections.

Understanding the Issue

In the provided Java code, a connection pool is created using a data source and managed by a bean. However, the code fails to close connections after they are used, causing the pool to quickly run out of available connections.

Identifying and Correcting Connection Leakage

The problem arises from a lack of proper closing of connections, statements, and result sets. To resolve this, JDBC resources should be closed within a try-with-resources block:

public void create(Entity entity) throws SQLException {
    try (
        Connection connection = dataSource.getConnection();
        PreparedStatement statement = connection.prepareStatement(SQL_CREATE);
    ) { 
        statement.setSomeObject(1, entity.getSomeProperty());
        // ...
        statement.executeUpdate();
    }
}

For Java versions prior to 7, a try-finally block with manual resource closing should be used:

public void create(Entity entity) throws SQLException {
    Connection connection = null;
    PreparedStatement statement = null;

    try { 
        connection = dataSource.getConnection();
        statement = connection.prepareStatement(SQL_CREATE);
        statement.setSomeObject(1, entity.getSomeProperty());
        // ...
        statement.executeUpdate();
    } finally {
        if (statement != null) try { statement.close(); } catch (SQLException logOrIgnore) {}
        if (connection != null) try { connection.close(); } catch (SQLException logOrIgnore) {}
    }
}

Closing Connections in Connection Pooling

It's essential to close connections even when using connection pooling. Connection pooling does not automatically handle closing; instead, it uses a wrapped connection that may return the connection to the pool rather than actually closing it.

Failure to close connections will prevent them from being returned to the pool and result in connection exhaustion. Proper closing ensures that connections are returned to the pool for reuse.

Additional Resources

For further information, refer to the following resources:

• [JDBC Connection Pooling in Oracle WebLogic Server](https://docs.oracle.com/cd/E24329_01/web.1211/e24485/xadatasrc.htm#CJADDHBB)
• [Closing JDBC Connections in Pool](https://www.onjava.com/pub/a/onjava/2003/05/29/closing-jdbc-connections-in-pool.html)
• [Managing JDBC Connections with Connection Pools](https://www.baeldung.com/java-jdbc-connection-pool)

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