如何解決Java Hibernate / C3P0錯誤：“無法獲取連接元數據。客戶端嘗試檢出Connection的嘗試已超時?！?？

如果您將C3P0的“ checkoutTimeout”屬性設置為非0的值，則可能是超時太快了（這是我的問題，解決方案：將其從500提高到2000毫秒）。

或者，有一種解決此警告的方法：

將hibernate.temp.use_jdbc_Metadata_defaults屬性設置為false。

在http://www.docjar.com/html/api/org/hibernate/cfg/SettingsFactory.java.html中可以找到此內容，但是如果不使用Hibernate提取JDBCMetadata默認值可能會產生副作用。

解決方法

我正在嘗試獲取一些傳遞并運行的代碼。它似乎使用了Hibernate框架。我已經克服了調整配置時的大多數錯誤，但這使我陷入了困境。

它正在嘗試連接到兩個數據庫：gameapp和gamelog。兩者都存在。似乎有問題連接到gamelog，但沒有問題連接到gameapp（在init之后，它可以連接并加載其他數據庫就很好了）。在下面，我粘貼了錯誤和異常堆棧轉儲。

我想像一下配置中還有其他內容，所以我還包括了該數據庫的配置文件。我知道這很模糊，但是我希望一些專業人士可以看到我所缺少的愚蠢錯誤。

<?xml version='1.0' encoding='GBK'?><!DOCTYPE hibernate-configuration PUBLIC '-//Hibernate/Hibernate Configuration DTD 3.0//EN' 'http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd'><hibernate-configuration> <session-factory><property name='dialect'>org.hibernate.dialect.MySQLDialect</property><property name='connection.driver_class'>com.mysql.jdbc.Driver</property><property name='connection.url'>jdbc:mysql://127.0.0.1:3306/gamelog</property><property name='connection.username'>root</property><property name='connection.password'></property><property name='connection.useUnicode'>true</property> <property name='connection.characterEncoding'>UTF-8</property> <property name='hibernate.jdbc.batch_size'>100</property><property name='jdbc.fetch_size'>1</property><property name='hbm2ddl.auto'>none</property><!-- update --><property name='connection.useUnicode'>true</property><property name='show_sql'>true</property><!-- c3p0-configuration --><property name='hibernate.connection.provider_class'>org.hibernate.connection.C3P0ConnectionProvider</property> <property name='hibernate.c3p0.min_size'>5</property><property name='hibernate.c3p0.max_size'>10</property><property name='hibernate.c3p0.timeout'>30</property><property name='hibernate.c3p0.idle_test_period'>30</property><property name='hibernate.c3p0.max_statements'>0</property><property name='hibernate.c3p0.acquire_increment'>5</property> </session-factory></hibernate-configuration>

異常和堆棧跟蹤：

2010-04-30 17:50:00,411 WARN [org.hibernate.cfg.SettingsFactory] - Could not obtain connection metadatajava.sql.SQLException: An attempt by a client to checkout a Connection has timed out. at com.mchange.v2.sql.SqlUtils.toSQLException(SqlUtils.java:106) at com.mchange.v2.sql.SqlUtils.toSQLException(SqlUtils.java:65) at com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool.checkoutPooledConnection(C3P0PooledConnectionPool.java:527) at com.mchange.v2.c3p0.impl.AbstractPoolBackedDataSource.getConnection(AbstractPoolBackedDataSource.java:128) at org.hibernate.connection.C3P0ConnectionProvider.getConnection(C3P0ConnectionProvider.java:35) at org.hibernate.cfg.SettingsFactory.buildSettings(SettingsFactory.java:76) at org.hibernate.cfg.Configuration.buildSettings(Configuration.java:1933) at org.hibernate.cfg.Configuration.buildSessionFactory(Configuration.java:1216) at com.database.hibernate.util.HibernateFactory.<init>(Unknown Source) at com.database.hibernate.util.HibernateUtil.<clinit>(Unknown Source) at com.server.databaseop.goodOp.GoodOpImpl.initBreedGoods(Unknown Source) at com.server.databaseop.goodOp.GoodOpImpl.access$000(Unknown Source) at com.server.databaseop.goodOp.GoodOpImpl$1.run(Unknown Source) at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:471) at java.util.concurrent.FutureTask$Sync.innerRunAndReset(FutureTask.java:351) at java.util.concurrent.FutureTask.runAndReset(FutureTask.java:178) at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$201(ScheduledThreadPoolExecutor.java:165) at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:267) at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1110) at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:603) at java.lang.Thread.run(Thread.java:636)Caused by: com.mchange.v2.resourcepool.TimeoutException: A client timed out while waiting to acquire a resource from com.mchange.v2.resourcepool.BasicResourcePool@ca470 -- timeout at awaitAvailable() at com.mchange.v2.resourcepool.BasicResourcePool.awaitAvailable(BasicResourcePool.java:1317) 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) ... 18 more