DEBUG -- CLOSE BY CLIENT STACK TRACE

在单元测试测试环境下主要参数两个错误信息：
1.java.lang.Exception: DEBUG STACK TRACE for PoolBackedDataSource.close().
这是一个异常信息，在com.mchange.v2.c3p0.impl.AbstractPoolBackedDataSource.close(AbstractPoolBackedDataSource.java:417)
方法中可以看到

public synchronized void close()
    {
        resetPoolManager();
        is_closed = true;
       
        C3P0Registry.markClosed(this);

        if (Debug.DEBUG && Debug.TRACE == Debug.TRACE_MAX && logger.isLoggable(MLevel.FINEST))
        {
            logger.log(MLevel.FINEST,
                    this.getClass().getName() + '@' + Integer.toHexString( System.identityHashCode( this ) ) +
                    " has been closed. ",
                    new Exception("DEBUG STACK TRACE for PoolBackedDataSource.close()."));
        }
    }

   if (Debug.DEBUG && Debug.TRACE == Debug.TRACE_MAX && logger.isLoggable(MLevel.FINEST))

这句判断中，只要log的debug级别打开，就可以确定会抛出这个Exception（奇怪的设计）。所以这个异常想要不出现，除了改log级别，没想到其他方式。

2.DEBUG -- CLOSE BY CLIENT STACK TRACE
[junit] java.lang.Exception: DEBUG -- CLOSE BY CLIENT STACK TRACE
    [junit]     at com.mchange.v2.c3p0.impl.NewPooledConnection.close(NewPooledConnection.java:566)
    [junit]     at com.mchange.v2.c3p0.impl.NewPooledConnection.close(NewPooledConnection.java:234)
    [junit]     at com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool$1PooledConnectionResourcePoolManager.destroyResource(C3P0PooledConnectionPool.java:470)
    [junit]     at com.mchange.v2.resourcepool.BasicResourcePool$1DestroyResourceTask.run(BasicResourcePool.java:964)
    [junit]     at com.mchange.v2.resourcepool.BasicResourcePool.destroyResource(BasicResourcePool.java:989)
    [junit]     at com.mchange.v2.resourcepool.BasicResourcePool.access$100(BasicResourcePool.java:32)
    [junit]     at com.mchange.v2.resourcepool.BasicResourcePool$5.run(BasicResourcePool.java:1174)


c3p0的配置如下
<!-- 数据源配置 -->
<bean id="dataSource" class="com.mchange.v2.c3p0.ComboPooledDataSource"
destroy-method="close">
<property name="driverClass" value="${connection.driver_class}" />
<property name="jdbcUrl" value="${jdbc.connection.url}" />
<property name="idleConnectionTestPeriod"
value="${jdbc.pool.c3p0.idle_connection_test_period}" />
<property name="preferredTestQuery" value="${jdbc.pool.c3p0.preferred_test_query}" />
<property name="maxIdleTime" value="${jdbc.pool.c3p0.max_idle_time}" />
<property name="properties">
<props>
<prop key="user">${jdbc.connection.username}</prop>
<prop key="password">${jdbc.connection.password}</prop>
<prop key="c3p0.acquire_increment">${jdbc.pool.c3p0.acquire_increment}</prop>
<prop key="c3p0.max_size">${jdbc.pool.c3p0.max_size}</prop>
<prop key="c3p0.min_size">${jdbc.pool.c3p0.min_size}</prop>
</props>
</property>
</bean>

这里原因主要和<bean id="dataSource" class="com.mchange.v2.c3p0.ComboPooledDataSource"
destroy-method="close">
这的destroy-method方法有关系。

Spring在读取这个配置文件以后，需要根据这些信息来实例化一些类，然后内部再根据中间的那些配置信息来实际构造数据源。
那么自然就不能保证这里的ComboPooledDataSource数据源一定是可用的，也不能保证close方法一定能关闭连接，对吧？Spring本身不能检查这个类是否真实有效，毫无Bug。实际上呢，也检查不了。同样的，close方法是否有效，也需要进行检查。

java.sql.Connection
public interface Connection extends Wrapper
任何一个JDBC数据库连接的实现类都应该实现这个接口的全部方法。比如，close。API里的描述是，立即释放此 Connection 对象的数据库和 JDBC 资源，而不是等待它们被自动释放。


     虽然API规定了close是关闭连接释放资源的。但这只是你接口的一厢情愿。也许人家实现厂家觉得close方法不够帅，要改成closeConnection。那。。。Spring总不好傻傻的去死扣close方法来关闭连接吧？虽然这方法必须实现，但是可没说一定要有内容啊。如果是空方法呢？所以有了destroy-method这个配置项的出现。

  总结:
     当不能确定destory-method的情况下,把该项删除,由程序自主选择关闭方法,这样Debug就不会报错了.


摘自http://csumissu.iteye.com/blog/1079576

评论

2 楼 liyixing1 2013-12-13  

793059909 写道

destroy-method="close"这一行去除了，还是报错：
[2013-12-06 11:06:21,715] [C3P0PooledConnectionPoolManager[identityToken->2tl0n98y1iwg7cbdzzq7a|719f1f]-HelperThread-#2] DEBUG - com.mchange.v2.c3p0.impl.NewPooledConnection@484c6b closed by a client.
java.lang.Exception: DEBUG -- CLOSE BY CLIENT STACK TRACE
at com.mchange.v2.c3p0.impl.NewPooledConnection.close(NewPooledConnection.java:646)
at com.mchange.v2.c3p0.impl.NewPooledConnection.closeMaybeCheckedOut(NewPooledConnection.java:259)
at com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool$1PooledConnectionResourcePoolManager.destroyResource(C3P0PooledConnectionPool.java:619)
at com.mchange.v2.resourcepool.BasicResourcePool$1DestroyResourceTask.run(BasicResourcePool.java:1024)
at com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread.run(ThreadPoolAsynchronousRunner.java:648)

源码中NewPooledConnection
的close方法有

if ( cause == null )
            {
                this.invalidatingException = NORMAL_CLOSE_PLACEHOLDER;

                if ( logger.isLoggable( MLevel.FINEST ) )
                    logger.log( MLevel.FINEST, this + " closed by a client.", new Exception("DEBUG -- CLOSE BY CLIENT STACK TRACE") );

                logCloseExceptions( null, closeExceptions );

                if (closeExceptions.size() > 0)
                    throw new SQLException("Some resources failed to close properly while closing " + this);
            }
            else
            {
                this.invalidatingException = cause;
                if (Debug.TRACE >= Debug.TRACE_MED)
                    logCloseExceptions( cause, closeExceptions );
                else
                    logCloseExceptions( cause, null );
            }

这几句，可以看出来，close方法被调用，就一定有这个DEBUG级别的异常信息产生。
destroy-method="close"去除之后，容器（数据源管理器）本身不会再主动调用释放资源的方法，个人猜测，你产生的原因有可能是因为你虽然修改了配置，但是并没有反应到最后运行时候的配置文件中，或者其他地方依然再进行过主动释放资源并调用清理资源的方法。

1 楼 793059909 2013-12-06  

destroy-method="close"这一行去除了，还是报错：
[2013-12-06 11:06:21,715] [C3P0PooledConnectionPoolManager[identityToken->2tl0n98y1iwg7cbdzzq7a|719f1f]-HelperThread-#2] DEBUG - com.mchange.v2.c3p0.impl.NewPooledConnection@484c6b closed by a client.
java.lang.Exception: DEBUG -- CLOSE BY CLIENT STACK TRACE
at com.mchange.v2.c3p0.impl.NewPooledConnection.close(NewPooledConnection.java:646)
at com.mchange.v2.c3p0.impl.NewPooledConnection.closeMaybeCheckedOut(NewPooledConnection.java:259)
at com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool$1PooledConnectionResourcePoolManager.destroyResource(C3P0PooledConnectionPool.java:619)
at com.mchange.v2.resourcepool.BasicResourcePool$1DestroyResourceTask.run(BasicResourcePool.java:1024)
at com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread.run(ThreadPoolAsynchronousRunner.java:648)