Tomcat中的c3p0數據庫連接池的釋放

一個項目通過c3p0獲得連接池，相關代碼如下：

public class JdbcUtil {
	
	// 連接池的核心類
	private static ComboPooledDataSource dataSource;
	
	//初始化連接池相關參數
	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);
			// 以下兩句用於設置自動重連
			dataSource.setIdleConnectionTestPeriod(10);
			dataSource.setTestConnectionOnCheckin(true);
		} catch (Exception e) {
			e.printStackTrace();
		}
	}
        //下面是getDataSource,getConnection等方法
}

關閉Tomcat的時候提示可能會造成內存泄漏：

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)

主要是這句：

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)

與這句

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)

查詢c3p0官方文檔

說明如下：c3p0 spawns a variety of Threads (helper threads, java.util.Timer threads)，結合上面的出錯信息，推斷應該是Tomcat關閉的時候沒有關閉JdbcUtil類創建出來的c3p0的datasource。

解決方案

寫一個監聽器，在其public void contextDestroyed方法中進行對c3p0數據源進行關閉就可以解決相關問題。

try {		
	DataSources.destroy(JdbcUtil.getDataSource());//getDataSource方法獲取c3p0數據源
	System.out.println("關閉數據庫連接池成功!");
} catch (SQLException e) {
	e.printStackTrace();
}

如果運行在Tomcat中的代碼啟動了Executor線程池，也需要在適當的地方(比如監聽器中的contextDestroyed方法)進行shutdown，否則會造成資源泄露。

從這個例子中也可以看出，直接使用spring、mybatis等管理數據源是多么省事。