We developed an application using Hibernate 2 and Oracle 9i two years ago. It had been deployed on an iPlanet server and was working fine.

We recently switched to Tomcat 5.5 (clustered - 2 servers). It ran fine for a few days and then began generating errors. They are intermittent and occur anywhere in the application where a database query is used. We are using Proxol 0.8.3.

A sample stack trace is:

net.sf.hibernate.LazyInitializationException: Exception initializing proxy: [crha.cara.biz.Service#1]
at net.sf.hibernate.proxy.LazyInitializer.initializeWrapExceptions(LazyInitializer.java:64)
at net.sf.hibernate.proxy.LazyInitializer.getImplementation(LazyInitializer.java:164)
at net.sf.hibernate.proxy.CGLIBLazyInitializer.intercept(CGLIBLazyInitializer.java:108)
at crha.cara.biz.Service$$EnhancerByCGLIB$$857218f8.isPsychologyArea(<generated>)
at crha.cara.servlet.EncounterServlet.getNewEncounter(EncounterServlet.java:127)
at crha.cara.servlet.EncounterServlet.doProcess(EncounterServlet.java:70)
at crha.cara.servlet.EncounterServlet.doPost(EncounterServlet.java:64)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:709)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:252)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:173)
at crha.cara.servlet.filter.SessionFilter.doFilter(SessionFilter.java:71)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:202)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:173)
at crha.servlet.filter.PersistenceSessionFilter.doFilter(PersistenceSessionFilter.java:117)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:202)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:173)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:213)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:178)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:482)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:126)
at org.apache.catalina.cluster.tcp.ReplicationValve.invoke(ReplicationValve.java:145)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:105)
at org.apache.catalina.valves.FastCommonAccessLogValve.invoke(FastCommonAccessLogValve.java:481)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:107)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:148)
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:856)
at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.processConnection(Http11Protocol.java:744)
at org.apache.tomcat.util.net.PoolTcpEndpoint.processSocket(PoolTcpEndpoint.java:527)
at org.apache.tomcat.util.net.LeaderFollowerWorkerThread.runIt(LeaderFollowerWorkerThread.java:80)
at org.apache.tomcat.util.threads.ThreadPool$ControlRunnable.run(ThreadPool.java:684)
at java.lang.Thread.run(Thread.java:595)
Caused by: net.sf.hibernate.JDBCException: could not load: [crha.cara.biz.Service#1]
at net.sf.hibernate.persister.EntityPersister.load(EntityPersister.java:422)
at net.sf.hibernate.impl.SessionImpl.doLoad(SessionImpl.java:2081)
at net.sf.hibernate.impl.SessionImpl.immediateLoad(SessionImpl.java:1899)
at net.sf.hibernate.proxy.LazyInitializer.initialize(LazyInitializer.java:53)
at net.sf.hibernate.proxy.LazyInitializer.initializeWrapExceptions(LazyInitializer.java:60)
... 31 more
Caused by: java.sql.SQLException: Closed Connection
at oracle.jdbc.dbaccess.DBError.throwSqlException(DBError.java:114)
at oracle.jdbc.dbaccess.DBError.throwSqlException(DBError.java:156)
at oracle.jdbc.dbaccess.DBError.throwSqlException(DBError.java:219)
at oracle.jdbc.driver.OracleConnection.prepareStatement(OracleConnection.java:337)
at sun.reflect.GeneratedMethodAccessor63.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:585)
at org.logicalcobwebs.proxool.ProxyConnection.invoke(ProxyConnection.java:68)
at org.logicalcobwebs.cglib.proxy.Proxy$ProxyImpl$$EnhancerByCGLIB$$b11be25c.prepareStatement(<generated>)
at net.sf.hibernate.impl.BatcherImpl.getPreparedStatement(BatcherImpl.java:249)
at net.sf.hibernate.impl.BatcherImpl.getPreparedStatement(BatcherImpl.java:223)
at net.sf.hibernate.impl.BatcherImpl.prepareQueryStatement(BatcherImpl.java:65)
at net.sf.hibernate.loader.Loader.prepareQueryStatement(Loader.java:704)
at net.sf.hibernate.loader.Loader.doQuery(Loader.java:185)
at net.sf.hibernate.loader.Loader.doQueryAndInitializeNonLazyCollections(Loader.java:133)
at net.sf.hibernate.loader.Loader.loadEntity(Loader.java:831)
at net.sf.hibernate.loader.Loader.loadEntity(Loader.java:851)
at net.sf.hibernate.loader.EntityLoader.load(EntityLoader.java:57)
at net.sf.hibernate.loader.EntityLoader.load(EntityLoader.java:49)
at net.sf.hibernate.persister.EntityPersister.load(EntityPersister.java:419)
... 35 more

Are there any suggestions?

check if the database closes connection after some time. in this case your session might be using a invalid connection.