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I am using connection pooling (c3p0-0.9.1.2) with Hibernate 3.2 like this: hibernate.cfg.xml

    <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/bspersonaltrainer</property>
    <property name="hibernate.connection.username">root</property>
    <property name="hibernate.connection.password">admin</property>
    <property name="hibernate.current_session_context_class">thread</property>
    <property name="hibernate.cache.provider_class">org.hibernate.cache.NoCacheProvider</property>
    <property name="hibernate.connection_provider_class">org.hibernate.connection.C3P0ConnectionProvider</property>
    <property name="hibernate.c3p0.min_size">2</property>
    <property name="hibernate.c3p0.max_size">400</property>
    <property name="hibernate.c3p0.max_statements">50</property>
    <property name="hibernate.c3p0.timeout">600</property>
    <property name="hibernate.c3p0.idle_test_period">300</property>
    <property name="hibernate.show_sql">false</property>

But i am getting this Exception frequently.

 Exception in thread "com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread-#1" java.lang.NoClassDefFoundError: com/mysql/jdbc/SQLError
    at com.mysql.jdbc.Util.handleNewInstance(Util.java:430)
    at com.mysql.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:302)
    at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:282)
    at com.mchange.v2.c3p0.DriverManagerDataSource.getConnection(DriverManagerDataSource.java:134)
    at com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:182)
    at com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:171)
    at com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool$1PooledConnectionResourcePoolManager.acquireResource(C3P0PooledConnectionPool.java:137)
    at com.mchange.v2.resourcepool.BasicResourcePool.doAcquire(BasicResourcePool.java:1014)
    at com.mchange.v2.resourcepool.BasicResourcePool.access$800(BasicResourcePool.java:32)
    at com.mchange.v2.resourcepool.BasicResourcePool$AcquireTask.run(BasicResourcePool.java:1810)
    at com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread.run(ThreadPoolAsynchronousRunner.java:547)
    Caused by: java.lang.ClassNotFoundException: com.mysql.jdbc.SQLError
    at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1680)
    at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1526)
    ... 11 more
  Exception in thread "com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread-#0" java.lang.NoClassDefFoundError: com/mysql/jdbc/SQLError
    at com.mysql.jdbc.Util.handleNewInstance(Util.java:430)
    at com.mysql.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:302)
    at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:282)
    at com.mchange.v2.c3p0.DriverManagerDataSource.getConnection(DriverManagerDataSource.java:134)
    at com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:182)
    at com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:171)
    at com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool$1PooledConnectionResourcePoolManager.acquireResource(C3P0PooledConnectionPool.java:137)
    at com.mchange.v2.resourcepool.BasicResourcePool.doAcquire(BasicResourcePool.java:1014)
    at com.mchange.v2.resourcepool.BasicResourcePool.access$800(BasicResourcePool.java:32)
    at com.mchange.v2.resourcepool.BasicResourcePool$AcquireTask.run(BasicResourcePool.java:1810)
    at com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread.run(ThreadPoolAsynchronousRunner.java:547)
16 Jan, 2013 10:44:42 AM org.apache.catalina.loader.WebappClassLoader loadClass
INFO: Illegal access: this web application instance has been stopped already.  Could not load com.mysql.jdbc.SQLError.  The eventual following stack trace is caused by an error thrown for debugging purposes as well as to attempt to terminate the thread which caused the illegal access, and has no functional impact.
java.lang.IllegalStateException
        at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1566)
        at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1526)
        at com.mysql.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:2103)
        at com.mysql.jdbc.ConnectionImpl.<init>(ConnectionImpl.java:718)
        at com.mysql.jdbc.JDBC4Connection.<init>(JDBC4Connection.java:46)
        at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
        at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:57)
        at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
        at java.lang.reflect.Constructor.newInstance(Constructor.java:532)
        at com.mysql.jdbc.Util.handleNewInstance(Util.java:406)
        at com.mysql.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:302)
        at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:282)
        at com.mchange.v2.c3p0.DriverManagerDataSource.getConnection(DriverManagerDataSource.java:134)
        at com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:182)
        at com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:171)
        at com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool$1PooledConnectionResourcePoolManager.acquireResource(C3P0PooledConnectionPool.java:137)
        at com.mchange.v2.resourcepool.BasicResourcePool.doAcquire(BasicResourcePool.java:1014)
        at com.mchange.v2.resourcepool.BasicResourcePool.access$800(BasicResourcePool.java:32)
        at com.mchange.v2.resourcepool.BasicResourcePool$AcquireTask.run(BasicResourcePool.java:1810)
        at com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread.run(ThreadPoolAsynchronousRunner.java:547)
16 Jan, 2013 10:44:42 AM org.apache.catalina.loader.WebappClassLoader loadClass
INFO: Illegal access: this web application instance has been stopped already.  Could not load com.mysql.jdbc.SQLError.  The eventual following stack trace is caused by an error thrown for debugging purposes as well as to attempt to terminate the thread which caused the illegal access, and has no functional impact.
java.lang.IllegalStateException
        at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1566)
        at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1526)
        at com.mysql.jdbc.Util.handleNewInstance(Util.java:430)
        at com.mysql.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:302)
        at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:282)
        at com.mchange.v2.c3p0.DriverManagerDataSource.getConnection(DriverManagerDataSource.java:134)
        at com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:182)
        at com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:171)
        at com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool$1PooledConnectionResourcePoolManager.acquireResource(C3P0PooledConnectionPool.java:137)
        at com.mchange.v2.resourcepool.BasicResourcePool.doAcquire(BasicResourcePool.java:1014)
        at com.mchange.v2.resourcepool.BasicResourcePool.access$800(BasicResourcePool.java:32)
        at com.mchange.v2.resourcepool.BasicResourcePool$AcquireTask.run(BasicResourcePool.java:1810)
        at com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread.run(ThreadPoolAsynchronousRunner.java:547)
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4

it looks like you may be forgetting to close your hibernate SessionFactory when you hot-restart your web app. this leave's c3p0's helper Threads from a dead instance (which in Tomcat implies a now-broken ClassLoader) running uselessly and causing problems.

c3p0 DataSources should be close()ed promptly when they will no longer be used, to release all pooled Connections and helper Threads. For web apps, this should often be done via a ServletContextListener. if your pool is managed by hibernate, promptly closing the SessionFactory should do the trick.

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2 Comments

i just get the session factory like this: sessionFactory = configuration.configure().buildSessionFactory(); and open and close session for every operation(insert,update,delete ). where to close this session factory if it didn't open yet.
so, i'm really not the guy to ask on hibernate issues (i'm the c3p0 guy.) but you need to understand and manage your resource life cycles. that line above to build the SessionFactory, where is it? it is setting up a bunch of resources for you. you need to understand when that happens and how you plan to clean them up. naively, i'd suggest both building and close()ing the SessionFactory in a ServletContextListener. but there might be other hibernate/tomcat "best practices" out there.

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