C3p0 trying to create a new connection pool and failing with ClassNotFoundException - spring

Question

I'm seeing a very strange behavior in my application.
My application setup: Spring + Hibernate + C3p0
Application keeps running fine, when all of a sudden I start seeing these errors in logs and system totally stop processing any database specific requests.
WARN c3p0.C3P0Registry - Could not create for find ConnectionCustomizer with class name ''.
java.lang.ClassNotFoundException:
at java.lang.Class.forName0(Native Method)
at java.lang.Class.forName(Class.java:169)
at com.mchange.v2.c3p0.C3P0Registry.getConnectionCustomizer(C3P0Registry.java:181)
at com.mchange.v2.c3p0.impl.C3P0PooledConnectionPoolManager.getConnectionCustomizer(C3P0PooledConnectionPoolManager.java:636)
at com.mchange.v2.c3p0.impl.C3P0PooledConnectionPoolManager.createPooledConnectionPool(C3P0PooledConnectionPoolManager.java:738)
at com.mchange.v2.c3p0.impl.C3P0PooledConnectionPoolManager.getPool(C3P0PooledConnectionPoolManager.java:257)
at com.mchange.v2.c3p0.impl.C3P0PooledConnectionPoolManager.getPool(C3P0PooledConnectionPoolManager.java:271)
at com.mchange.v2.c3p0.impl.AbstractPoolBackedDataSource.getConnection(AbstractPoolBackedDataSource.java:128)
at org.springframework.orm.hibernate3.LocalDataSourceConnectionProvider.getConnection(LocalDataSourceConnectionProvider.java:80)
at org.hibernate.jdbc.ConnectionManager.openConnection(ConnectionManager.java:423)
at org.hibernate.jdbc.ConnectionManager.getConnection(ConnectionManager.java:144)
at org.hibernate.jdbc.AbstractBatcher.prepareSelectStatement(AbstractBatcher.java:123)
at org.hibernate.id.SequenceGenerator.generate(SequenceGenerator.java:73)
at org.hibernate.event.def.AbstractSaveEventListener.saveWithGeneratedId(AbstractSaveEventListener.java:99)
at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.saveWithGeneratedOrRequestedId(DefaultSaveOrUpdateEventListener.java:187)
at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.entityIsTransient(DefaultSaveOrUpdateEventListener.java:172)
at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.performSaveOrUpdate(DefaultSaveOrUpdateEventListener.java:94)
at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.onSaveOrUpdate(DefaultSaveOrUpdateEventListener.java:70)
at org.hibernate.impl.SessionImpl.fireSaveOrUpdate(SessionImpl.java:507)
at org.hibernate.impl.SessionImpl.saveOrUpdate(SessionImpl.java:499)
at org.hibernate.impl.SessionImpl.saveOrUpdate(SessionImpl.java:495)
at org.springframework.orm.hibernate3.HibernateTemplate$18.doInHibernate(HibernateTemplate.java:690)
at org.springframework.orm.hibernate3.HibernateTemplate.execute(HibernateTemplate.java:365)
at org.springframework.orm.hibernate3.HibernateTemplate.saveOrUpdate(HibernateTemplate.java:687)
Why would C3p0 require to create a new connection pool at this
particular time, before these exceptions application is 100% working
fine and responding perfectly.
Also I've not provided any connectionCustomizerClassName property in
my c3p0 configurations, why would it load one? in this stack trace I
see it's not-null empty string ''.
Any clues?
==============================================================================
Following hibernate jars I see in application's classpath:
hibernate-3.2.6.ga.jar
spring-hibernate-1.2.6.jar
Following c3p0 jars I see in application's classpath:
c3p0-0.9.1.jar
c3p0-0.9.2-pre5.jar
c3p0-oracle-thin-extras-0.9.2-pre5.jar
Code that manually read these properties and set on datasource (I do not read/set any connectionCustomizerClassName property here at all)
ComboPooledDataSource dataSource = new ComboPooledDataSource();
dataSource.setMinPoolSize(Integer.parseInt(props.getProperty("jdbc.hibernate.c3p0.minPoolSize")));
.....
Here are C3p0 properties being used:
jdbc.hibernate.c3p0.minPoolSize=100
jdbc.hibernate.c3p0.initialPoolSize=100
jdbc.hibernate.c3p0.maxPoolSize=1000
jdbc.hibernate.c3p0.maxIdleTime=21600
jdbc.hibernate.c3p0.maxStatementsPerConnection=0
jdbc.hibernate.c3p0.maxStatements=0
jdbc.hibernate.c3p0.numHelperThreads=30
jdbc.hibernate.c3p0.checkoutTimeout=30000
jdbc.hibernate.c3p0.idleConnectionTestPeriod=900
jdbc.hibernate.c3p0.preferredTestQuery=SELECT 1 FROM dual
jdbc.hibernate.c3p0.maxConnectionAge=0
jdbc.hibernate.c3p0.maxIdleTimeExcessConnections=3600
jdbc.hibernate.c3p0.acquireIncrement=10
jdbc.hibernate.c3p0.acquireRetryDelay=5000
jdbc.hibernate.c3p0.acquireRetryAttempts=6
jdbc.hibernate.c3p0.propertyCycle=180

Answer 1

Following up a conversation in the comments on the posted question, it looks like the issue here is that VisualVM updates the null valued property connectionCustomizerClassName to an empty String value, which c3p0 currently treats an non-null and interprets as a class name.
Going forward (c3p0-0.9.5-pre7 and above), c3p0 will guard against this, interpret an all-whitespace connectionCustomizerClassName as equivalent to null. But in the meantime or for older versions, take care.
One easy workaround would be to define a NullConnectionCustomizer:
package mypkg;
import com.mchange.v2.c3p0.*;
public class NullConnectionCustomizer extends AbstractConnectionCustomizer
{}
And then use mypkg.NullConnectionCustomizer for connectionCustomizerClassName, so that the corresponding field in VisualVM is not empty and ambiguously interpretable as empty String or null.