Tomcat中的c3p0数据库连接池的释放

一个项目通过c3p0获得连接池，相关代码如下：

public class JdbcUtil {
	
	// 连接池的核心类
	private static ComboPooledDataSource dataSource;
	
	//初始化连接池相关参数
	static{
		try {
			dataSource = new ComboPooledDataSource();
			dataSource.setDriverClass(PropertiesUtil.getValue("jdbcName"));
			dataSource.setJdbcUrl(PropertiesUtil.getValue("dbUrl"));
			dataSource.setUser(PropertiesUtil.getValue("dbUserName"));
			dataSource.setPassword(PropertiesUtil.getValue("dbPassword"));
			dataSource.setInitialPoolSize(5);
			dataSource.setMinPoolSize(5);
			dataSource.setMaxPoolSize(20);
			// 以下两句用于设置自动重连
			dataSource.setIdleConnectionTestPeriod(10);
			dataSource.setTestConnectionOnCheckin(true);
		} catch (Exception e) {
			e.printStackTrace();
		}
	}
        //下面是getDataSource,getConnection等方法
}

关闭Tomcat的时候提示可能会造成内存泄漏：

警告: The web application [uavmonitor] appears to have started a thread named [Timer-0] but has failed to stop it. This is very likely to create a memory leak. Stack trace of thread:
 java.lang.Object.wait(Native Method)
 java.util.TimerThread.mainLoop(Timer.java:552)
 java.util.TimerThread.run(Timer.java:505)
二月 13, 2017 3:51:45 下午 org.apache.catalina.loader.WebappClassLoaderBase clearReferencesThreads
警告: The web application [uavmonitor] appears to have started a thread named [com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread-#0] but has failed to stop it. This is very likely to create a memory leak. Stack trace of thread:
 java.lang.Object.wait(Native Method)
 com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread.run(ThreadPoolAsynchronousRunner.java:534)
二月 13, 2017 3:51:45 下午 org.apache.catalina.loader.WebappClassLoaderBase clearReferencesThreads
警告: The web application [uavmonitor] appears to have started a thread named [com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread-#1] but has failed to stop it. This is very likely to create a memory leak. Stack trace of thread:
 java.lang.Object.wait(Native Method)
 com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread.run(ThreadPoolAsynchronousRunner.java:534)
二月 13, 2017 3:51:45 下午 org.apache.catalina.loader.WebappClassLoaderBase clearReferencesThreads
警告: The web application [uavmonitor] appears to have started a thread named [com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread-#2] but has failed to stop it. This is very likely to create a memory leak. Stack trace of thread:
 java.lang.Object.wait(Native Method)
 com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread.run(ThreadPoolAsynchronousRunner.java:534)

主要是这句：

警告: The web application [uavmonitor] appears to have started a thread named [com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread-#0] but has failed to stop it. This is very likely to create a memory leak. Stack trace of thread:
 java.lang.Object.wait(Native Method)
 com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread.run(ThreadPoolAsynchronousRunner.java:534)

与这句

The web application [uavmonitor] appears to have started a thread named [Timer-0] but has failed to stop it. This is very likely to create a memory leak. Stack trace of thread:
 java.lang.Object.wait(Native Method)
 java.util.TimerThread.mainLoop(Timer.java:552)
 java.util.TimerThread.run(Timer.java:505)

查询c3p0官方文档

说明如下：c3p0 spawns a variety of Threads (helper threads, java.util.Timer threads)，结合上面的出错信息，推断应该是Tomcat关闭的时候没有关闭JdbcUtil类创建出来的c3p0的datasource。

解决方案

写一个监听器，在其public void contextDestroyed方法中进行对c3p0数据源进行关闭就可以解决相关问题。

try {		
	DataSources.destroy(JdbcUtil.getDataSource());//getDataSource方法获取c3p0数据源
	System.out.println("关闭数据库连接池成功!");
} catch (SQLException e) {
	e.printStackTrace();
}

如果运行在Tomcat中的代码启动了Executor线程池，也需要在适当的地方(比如监听器中的contextDestroyed方法)进行shutdown，否则会造成资源泄露。

从这个例子中也可以看出，直接使用spring、mybatis等管理数据源是多么省事。