How to Fix the \'com.mysql.jdbc.exceptions.jdbc4.MySQLNonTransientConnectionException: No operations allowed after connection closed\' Error in Hibernate?

Diagnosing the "com.mysql.jdbc.exceptions.jdbc4.MySQLNonTransientConnectionException: No operations allowed after connection closed" Error

When using Hibernate with remote connections, you may encounter a "No operations allowed after connection closed" error due to broken connections. By default, MySQL has a wait_timeout setting that can cause the connection to close after a period of inactivity. This can happen during extended application runs or if there is network instability.

Connection Pooling with C3P0

To address this issue, it's recommended to use a connection pooling library like C3P0. Hibernate's native connection pooling is limited and not suitable for production environments. Connection pooling establishes a pool of connections that are managed and reused by the application, reducing the overhead of establishing new connections for each query.

Configuring C3P0 with Hibernate

Here's an updated configuration file using C3P0:

<property name="hibernate.dialect">org.hibernate.dialect.MySQLDialect</property>
<property name="hibernate.connection.driver_class">com.mysql.jdbc.Driver</property>
<property name="hibernate.connection.url">jdbc:mysql://localhost:3306/xyz</property>
<property name="hibernate.connection.username">root</property>
<property name="hibernate.connection.password">root</property>
<property name="hibernate.show_sql">false</property>
<property name="hibernate.current_session_context_class">thread</property>
<property name="hibernate.query.factory_class">org.hibernate.hql.ast.ASTQueryTranslatorFactory</property>

<property name="connection.provider_class">org.hibernate.connection.C3P0ConnectionProvider</property>
<property name="c3p0.acquire_increment">1</property>
<property name="c3p0.idle_test_period">100</property> <!-- seconds -->
<property name="c3p0.max_size">100</property>
<property name="c3p0.max_statements">0</property>
<property name="c3p0.min_size">10</property>
<property name="c3p0.timeout">3600</property> <!-- seconds -->

In this configuration, the C3P0 connection provider is enabled with the appropriate settings for pool size, timeout, and connection testing.

Other Potential Causes

If connection pooling does not resolve the issue, it's worth investigating other potential causes, such as:

• Firewall or network settings blocking connections
• MySQL configuration issues, such as incorrect user permissions or outdated JDBC driver
• Memory or resource constraints on the server or application

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