No operations allowed after connection closed

异常信息如下：

org.springframework.dao.DataAccessResourceFailureException: could not prepare statement; nested exception is org.hibernate.exception.JDBCConnectionException: could not prepare statementat org.springframework.orm.hibernate4.SessionFactoryUtils.convertHibernateAccessException(SessionFactoryUtils.java:142)at org.springframework.orm.hibernate4.SpringSessionSynchronization.beforeCommit(SpringSessionSynchronization.java:102)at org.springframework.transaction.support.TransactionSynchronizationUtils.triggerBeforeCommit(TransactionSynchronizationUtils.java:95)at org.springframework.transaction.support.AbstractPlatformTransactionManager.triggerBeforeCommit(AbstractPlatformTransactionManager.java:928)at org.springframework.transaction.support.AbstractPlatformTransactionManager.processCommit(AbstractPlatformTransactionManager.java:740)at org.springframework.transaction.support.AbstractPlatformTransactionManager.commit(AbstractPlatformTransactionManager.java:726)at org.springframework.transaction.interceptor.TransactionAspectSupport.commitTransactionAfterReturning(TransactionAspectSupport.java:496)at org.springframework.transaction.interceptor.TransactionAspectSupport.invokeWithinTransaction(TransactionAspectSupport.java:276)

Caused by: org.hibernate.exception.JDBCConnectionException: could not prepare statementat org.hibernate.exception.internal.SQLExceptionTypeDelegate.convert(SQLExceptionTypeDelegate.java:65)at org.hibernate.exception.internal.StandardSQLExceptionConverter.convert(StandardSQLExceptionConverter.java:49)at org.hibernate.engine.jdbc.spi.SqlExceptionHelper.convert(SqlExceptionHelper.java:126)at org.hibernate.engine.jdbc.internal.StatementPreparerImpl$StatementPreparationTemplate.prepareStatement(StatementPreparerImpl.java:196)at org.hibernate.engine.jdbc.internal.StatementPreparerImpl.prepareStatement(StatementPreparerImpl.java:96)at org.hibernate.engine.jdbc.batch.internal.AbstractBatchImpl.buildBatchStatement(AbstractBatchImpl.java:152)at org.hibernate.engine.jdbc.batch.internal.AbstractBatchImpl.getBatchStatement(AbstractBatchImpl.java:141)at org.hibernate.persister.entity.AbstractEntityPersister.update(AbstractEntityPersister.java:3232)at org.hibernate.persister.entity.AbstractEntityPersister.updateOrInsert(AbstractEntityPersister.java:3183)at org.hibernate.persister.entity.AbstractEntityPersister.update(AbstractEntityPersister.java:3525)at org.hibernate.action.internal.EntityUpdateAction.execute(EntityUpdateAction.java:159)at org.hibernate.engine.spi.ActionQueue.executeActions(ActionQueue.java:463)at org.hibernate.engine.spi.ActionQueue.executeActions(ActionQueue.java:349)at org.hibernate.event.internal.AbstractFlushingEventListener.performExecutions(AbstractFlushingEventListener.java:350)at org.hibernate.event.internal.DefaultFlushEventListener.onFlush(DefaultFlushEventListener.java:56)at org.hibernate.internal.SessionImpl.flush(SessionImpl.java:1222)at org.springframework.orm.hibernate4.SpringSessionSynchronization.beforeCommit(SpringSessionSynchronization.java:99)... 26 moreCaused by: com.mysql.jdbc.exceptions.jdbc4.MySQLNonTransientConnectionException: No operations allowed after connection closed.at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)at java.lang.reflect.Constructor.newInstance(Constructor.java:423)at com.mysql.jdbc.Util.handleNewInstance(Util.java:411)at com.mysql.jdbc.Util.getInstance(Util.java:386)at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:1015)at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:989)at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:975)at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:920)at com.mysql.jdbc.ConnectionImpl.throwConnectionClosedException(ConnectionImpl.java:1304)at com.mysql.jdbc.ConnectionImpl.checkClosed(ConnectionImpl.java:1296)at com.mysql.jdbc.ConnectionImpl.prepareStatement(ConnectionImpl.java:4511)at com.mysql.jdbc.ConnectionImpl.prepareStatement(ConnectionImpl.java:4476)at com.mchange.v2.c3p0.impl.NewProxyConnection.prepareStatement(NewProxyConnection.java:567)at org.hibernate.engine.jdbc.internal.StatementPreparerImpl$1.doPrepare(StatementPreparerImpl.java:103)at org.hibernate.engine.jdbc.internal.StatementPreparerImpl$StatementPreparationTemplate.prepareStatement(StatementPreparerImpl.java:186)... 39 more

之前偶尔会产生这个问题，昨晚发送邮件时发现了这个异常，猜测是配置文件问题，今天修改了Hibernate的配置文件之后测试发现问题重现，由于C3P0数据库连接池一直有问题，我之前是加入了unreturnedConnectionTimeout属性，我修改值为1之后就发现了问题。

<property name="unreturnedConnectionTimeout" value="1"/>

这个值的解释：“设置连接被checkout后，经过多长时间还未返还连接池，则连接缓冲池直接Kill该连接”，所以简单地说，如果有一个方法（并且有操作数据库）的执行时间大于了设置的unreturnedConnectionTimeout之后，如果方法在最后的时候还要操作数据库的话，那么就会报异常，原因就是：No operations allowed after connection closed。因为connection已经被连接池直接Kill掉了，所以无法继续操作数据库，因此报错。

总结：

<property name="unreturnedConnectionTimeout" value="1"/>这个属性不要随便设置，我是由于数据库有连接池泄露问题迟迟没有解决，所以加入的这个属性。如果你也跟我一样，必须加入这个属性来强行关闭连接，那么需要注意，这个值应该大于你的所有方法执行的最大时间。