After my tomcat server has been running successfully for a day I get the below stacktrace. All the forums I've read say that the solution is just to configure c3p0, but I thought I had. i.e. This is my hibernate.cfg.xml file:

<!DOCTYPE hibernate-configuration SYSTEM "http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">
<hibernate-configuration>
<session-factory>
<property name="hibernate.connection.driver_class">com.mysql.jdbc.Driver</property>
<property name="hibernate.connection.url">jdbc:mysql://localhost:3306/togetherdining</property>
<property name="hibernate.connection.username">user</property>
<property name="hibernate.connection.password">pass</property>
<property name="hibernate.dialect">org.hibernate.dialect.HSQLDialect</property>

<!-- Use the C3P0 connection pool provider -->
<property name="hibernate.c3p0.min_size">5</property>
<property name="hibernate.c3p0.max_size">20</property>
<property name="hibernate.c3p0.timeout">300</property>
<property name="hibernate.c3p0.max_statements">50</property>
<property name="hibernate.c3p0.idle_test_period">3000</property>

<!-- Show and print nice SQL on stdout -->
<property name="show_sql">true</property>
<property name="format_sql">true</property>

<!-- List of XML mapping files -->
<mapping resource="com/togetherdining/db/beans/togetherdining.hbm.xml"/>
</session-factory>
</hibernate-configuration>

What else do I need to do? What check can I make?

StackTrace:
com.mysql.jdbc.exceptions.jdbc4.MySQLNonTransientConnectionException: Connection.close() has already been called. Invalid operation in this state.
sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:39)
sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:27)
java.lang.reflect.Constructor.newInstance(Constructor.java:513)
com.mysql.jdbc.Util.handleNewInstance(Util.java:406)
com.mysql.jdbc.Util.getInstance(Util.java:381)
com.mysql.jdbc.SQLError.createSQLException(SQLError.java:984)
com.mysql.jdbc.SQLError.createSQLException(SQLError.java:956)
com.mysql.jdbc.SQLError.createSQLException(SQLError.java:926)
com.mysql.jdbc.ConnectionImpl.getMutex(ConnectionImpl.java:3117)
com.mysql.jdbc.ConnectionImpl.rollback(ConnectionImpl.java:4726)
org.hibernate.transaction.JDBCTransaction.rollbackAndResetAutoCommit(JDBCTransaction.java:217)
org.hibernate.transaction.JDBCTransaction.rollback(JDBCTransaction.java:196)
com.togetherdining.util.HibernateUtil.handleError(HibernateUtil.java:37)
com.togetherdining.tags.infra.DBTagBase.processStartTag(DBTagBase.java:38)
com.togetherdining.tags.infra.TagBase.doStartTag(TagBase.java:24)
org.apache.jsp.planDinner_jsp._jspService(planDinner_jsp.java:164)
org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:374)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:342)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:267)
javax.servlet.http.HttpServlet.service(HttpServlet.java:717)


Thanks in advance. I hope somebody can help.

Ok, I've noticed this in my logs:

[main] INFO org.hibernate.connection.DriverManagerConnectionProvider - Using Hibernate built-in connection pool (not for production use!)

so obviously it's not actually using c3p0. Anybody know what more I need to do to make it use c3p0?

Got it!

I downloaded the hibernate sourcecode and after some debugging in the ConnectionProviderFactory, turns out that the logic that sets up the C3P0ConnectionProvider wasn't added until hibernate 3.5.*, and I'm using 3.3.1 (woops).

Two solutions:
1. upgrade to the latest hibernate
2. Add this hibernate property to tell hibernate which provider to use:
hibernate.connection.provider_class = org.hibernate.connection.C3P0ConnectionProvider

I've gone with (2) for now to avoid the risk of anything else breaking.