【发布时间】：2013-11-25 15:10:46
【问题描述】：
我正在使用 Servlet 2.4、Hibernate 4.2.4 Final、c3p0 0.9.2.1、Tomcat 7.0.42、MySQL 5.6 和 JSP。
我使用 Oracle 11gR2 DB 完成了开发，但后来被要求切换到 MySQL 作为数据库。
我手头有一个不寻常的问题。
问题是为每个单独的数据库请求创建多个 MySQL 进程/连接，尽管发出了 SessionFactoryUtil.close();，但它们既没有关闭也没有返回到池中，而 Oracle 数据库不是这种情况。
我在这两个不同的数据库上测试了完全相同的代码，即在执行函数/请求（例如：登录）之后
应用程序在使用 Oracle (11gR2) 进行测试时，数据库创建了一个连接并将其用于以后的所有请求。
SELECT * FROM V$RESOURCE_LIMIT
给我以下输出
RESOURCE_NAME：进程
CURRENT_UTILIZATION：32
MAX_UTILIZATION：36
INITIAL_ALLOCATION：300
LIMIT_VALUE：300
无论有多少用户登录，连接池都会优雅地维护它。
另一方面，当同一个应用程序在 MySQL 上运行时：
我在 MySQL 上做了一个SHOW PROCESSLIST;，它显示了为每个请求创建了两个进程； c3p0 成功终止了一个连接，但另一个连接仍然存在，直到数据库崩溃，因为它超过了可用的最大连接数。
我的 SessionFactoryUtil 非常简单明了，如下：
public class SessionFactoryUtil {
private static SessionFactory sessionFactory;
public static SessionFactory getSessionFactory() {
return sessionFactory = new Configuration().configure()
.buildSessionFactory();//deprecated method not changed due to official reason
}
public Session getCurrentSession() {
return sessionFactory.getCurrentSession();
}
public static void close() {
if (sessionFactory != null) {
sessionFactory.close();
}
sessionFactory = null;
}
我的DAO方法如下
public User getUserByName(String userName) throws FetchException {
User user = null;
Session session = SessionFactoryUtil.getSessionFactory().getCurrentSession();
try {
session.beginTransaction();
user = (User) session.createQuery("from User where userName = '" + userName + "'").uniqueResult();
} catch (Exception e) {
logger.info("UserDaoImpl -> getUserByName() : Error : " +e);
e.printStackTrace();
} finally {
SessionFactoryUtil.close();
}
return user;
c3p0 销毁连接的堆栈跟踪如下：
20:45:43,692 INFO com.mchange.v2.resourcepool.BasicResourcePool:1493 - A checked-out resource is overdue, and will be destroyed: com.mchange.v2.c3p0.impl.NewPooledConnection@61f31fff
20:45:43,692 INFO com.mchange.v2.resourcepool.BasicResourcePool:1496 - Logging the stack trace by which the overdue resource was checked-out.
java.lang.Exception: DEBUG STACK TRACE: Overdue resource check-out stack trace.
at com.mchange.v2.resourcepool.BasicResourcePool.checkoutResource(BasicResourcePool.java:555)
at com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool.checkoutAndMarkConnectionInUse(C3P0PooledConnectionPool.java:755)
at com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool.checkoutPooledConnection(C3P0PooledConnectionPool.java:682)
at com.mchange.v2.c3p0.impl.AbstractPoolBackedDataSource.getConnection(AbstractPoolBackedDataSource.java:140)
at org.hibernate.service.jdbc.connections.internal.C3P0ConnectionProvider.getConnection(C3P0ConnectionProvider.java:84)
at org.hibernate.internal.AbstractSessionImpl$NonContextualJdbcConnectionAccess.obtainConnection(AbstractSessionImpl.java:292)
at org.hibernate.engine.jdbc.internal.LogicalConnectionImpl.obtainConnection(LogicalConnectionImpl.java:214)
at org.hibernate.engine.jdbc.internal.LogicalConnectionImpl.getConnection(LogicalConnectionImpl.java:157)
at org.hibernate.engine.transaction.internal.jdbc.JdbcTransaction.doBegin(JdbcTransaction.java:67)
at org.hibernate.engine.transaction.spi.AbstractTransactionImpl.begin(AbstractTransactionImpl.java:160)
at org.hibernate.internal.SessionImpl.beginTransaction(SessionImpl.java:1426)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at org.hibernate.context.internal.ThreadLocalSessionContext$TransactionProtectionWrapper.invoke(ThreadLocalSessionContext.java:352)
at com.sun.proxy.$Proxy7.beginTransaction(Unknown Source)
at com.demo.access.impl.ConfDaoImp.showAllEvents(ConfDaoImp.java:939)
at com.demo.business.impl.ConfServiceImpl.showAllEvents(ConfServiceImpl.java:404)
at com.demo.controller.UserController.getControls(UserController.java:112)
at com.demo.controller.UserController.validateUser(UserController.java:93)
at com.demo.controller.UserController.process(UserController.java:42)
at com.demo.controller.ApplicationServlet.process(ApplicationServlet.java:75)
at com.demo.controller.ApplicationServlet.doPost(ApplicationServlet.java:53)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:641)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:722)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:304)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
at com.demo.controller.LoginFilter.doFilter(LoginFilter.java:37)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:224)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:185)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:472)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:151)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:100)
at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:929)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:405)
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:269)
at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:515)
at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:302)
at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
at java.lang.Thread.run(Unknown Source)
我已经阅读了几乎所有与此特定场景相关的问题，但似乎没有一个有效，或者线程被中途放弃，或者我错过了一些东西；有人可以帮我解决这个问题。
【问题讨论】：
标签： mysql oracle hibernate servlets