我有一个使用c3p0进行连接池的应用程序。当连接到数据库时出现任何问题时，我会得到如下例外：
java.sql.SQLException: An SQLException was provoked by the following failure:
com.mchange.v2.resourcepool.ResourcePoolException: A ResourcePool cannot acquire
a new resource -- the factory or source appears to be down.
at com.mchange.v2.sql.SqlUtils.toSQLException(SqlUtils.java:106)
at com.mchange.v2.sql.SqlUtils.toSQLException(SqlUtils.java:65)
at com.mchange.v2.sql.SqlUtils.toSQLException(SqlUtils.java:62)
at com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool.checkoutPooledConnection(C3P0PooledConnectionPool.java:531)
at com.mchange.v2.c3p0.impl.AbstractPoolBackedDataSource.getConnection(AbstractPoolBackedDataSource.java:128)
at com.pontiflex.monitor.dao.ConnectionManager.getConfigReadOnlyDbConnection(Unknown Source)
at com.pontiflex.monitor.dao.MonitorServiceDAO.getLiveIOCountForOrganization(Unknown Source) at com.pontiflex.monitor.BillingMonitor.getComparisonValueForActivation(Unknown Source)
at com.pontiflex.monitor.AbstractMonitor.isMonitoringActive(Unknown Source)
at com.pontiflex.monitor.AbstractMonitor.generateAlerts(Unknown Source)
at com.pontiflex.monitor.AbstractMonitor.doMonitoring(Unknown Source)
at com.pontiflex.monitor.worker.MonitorWorker.run(Unknown Source)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:439)
at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:303)
at java.util.concurrent.FutureTask.run(FutureTask.java:138) at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:895)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:918)
at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:895)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:918)
at java.lang.Thread.run(Thread.java:662)
Caused by: com.mchange.v2.resourcepool.ResourcePoolException: A ResourcePool cannot
acquire a new resource -- the factory or source appears to be down.
at com.mchange.v2.resourcepool.BasicResourcePool.awaitAvailable(BasicResourcePool.java:1279)
at com.mchange.v2.resourcepool.BasicResourcePool.prelimCheckoutResource(BasicResourcePool.java:557)
at com.mchange.v2.resourcepool.BasicResourcePool.checkoutResource(BasicResourcePool.java:477)
at com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool.checkoutPooledConnection(C3P0PooledConnectionPool.java:525)
... 14 more
无论是网络连接问题，服务器问题（连接太多）还是配置问题，都会出现同样的异常。如果我打开mysql jdbc驱动程序和c3p0的调试日志记录，我会得到更多信息：
WARN com.mchange.v2.resourcepool.BasicResourcePool
com.mchange.v2.resourcepool.BasicResourcePool$AcquireTask@4e074784 --
Acquisition Attempt Failed!!! Clearing pending acquires. While trying
to acquire a needed new resource, we failed to succeed more than the
maximum number of allowed acquisition attempts (30). Last acquisition
attempt exception:
com.mysql.jdbc.exceptions.MySQLNonTransientConnectionException: Data
source rejected establishment of connection, message from server:
"Too many connections"
at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:921)
at com.mysql.jdbc.MysqlIO.doHandshake(MysqlIO.java:1070)
at com.mysql.jdbc.Connection.createNewIO(Connection.java:2775)
at com.mysql.jdbc.Connection.<init>(Connection.java:1555)
at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:285)
at com.mchange.v2.c3p0.DriverManagerDataSource.getConnection(DriverManagerDataSource.java:135)
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)
在没有调整记录器配置的情况下抛出ResourcePoolException时，我能做些什么来让c3p0给我根本原因？
答案 0 :(得分：4)
SQLException是允许JDBC apis抛出的（已检查）异常，因此c3p0必须“包装”以常规方式不是SQLExceptions的基础异常。如果要检查特定内容，则在这些异常上调用getCause（）将传递原始的Throwable。
在你引用的特定例子中，发生了一些不同的事情。问题是记录Exception的Thread不是您的客户端Thread。 c3p0-internal线程从数据库获取Connections。您的客户端线程从池中获取连接。这两个活动与c3p0可以管理的解耦一样 - 这就是拥有连接池的重点。首先，内部线程执行“一轮”采集尝试（默认情况下为30次尝试，延迟时间为1秒，但如果需要，可以重新配置）。
如果获取连接的所有尝试都失败，则c3p0内部线程......
1）记录失败，并在尝试时看到最后一个异常。这是你引用的第二个例外。请注意，这是在WARNING中记录的，而不是DEBUG级别。如果您在INFO上有c3p0日志 - 你应该 - 你会看到这些消息。 [如果你想查看每个单独的Exception，在声明失败之前必须发生的所有30个异常（在defailts下），你需要将记录转为DEBUG（或FINE或ALL）。]
2）在记录采集系列失败后，c3p0将中断wait（）客户端并发出ResourcePoolException信号，该信号变为SQLException。这是您引用的第一个例外。发出ResourcePoolException信号。
3）如果breakAfterAcquireFailure设置为false（默认值），则池将从采集失败中恢复。当新客户端进入时，它将再次尝试获取新的Connections。但是，如果breakAfterAcquireFailure设置为true，则池将始终响应具有异常的新客户端请求。
无论如何，我希望这不是完全没有用的。 c3p0可以定义一个自定义的Exception类型，它将成为传递给客户端的包装Exception的原因，因此客户端可以测试代码中的获取失败，但至少目前它没有。抱歉！