commons-pool实战之 PoolableObjectFactory和ObjectPool

工作中需要减少对一些比较耗系统资源对象的创建和初始化工作，因此想到了apache commons-pool工具包。commons-pool包里主要包括三个重要的接口：

ObjectPool用于管理要被池化的对象的借出和归还；

ObjectPoolFactory用于大量生成相同类型和设置的ObjectPool。

看看下面的例子

一个Connection类，可以想象成一个远程连接比如数据库连接等。其中包括创建连接，关闭连接，和一个print方法。

package com.googlecode.garbagecan.commons.pool.sample1; import org.slf4j.Logger; import org.slf4j.LoggerFactory; public class MyConnection { private static Logger logger = LoggerFactory.getLogger(MyConnection.class); private String name; private boolean connected; public MyConnection(String name) { this.name = name; } public void connect() { this.connected = true; logger.info(name + ": " + connected); } public void close() { this.connected = false; logger.info(name + ": " + connected); } public boolean isConnected() { return this.connected; } public String getName() { return this.name; } public void print() { logger.info(this.name); } } 一个PoolableObjectFactory接口的实现类，提供makeObject, activateObject, passivateObject, validateObject, destroyObject方法。

package com.googlecode.garbagecan.commons.pool.sample1; import org.apache.commons.pool.PoolableObjectFactory; import org.slf4j.Logger; import org.slf4j.LoggerFactory; public class MyConnectionPoolableObjectFactory implements PoolableObjectFactory { private static Logger logger = LoggerFactory.getLogger(MyConnectionPoolableObjectFactory.class); private static int count = 0; public Object makeObject() throws Exception { MyConnection myConn = new MyConnection("conn_" + (++count)); myConn.connect(); logger.info(myConn.getName()); return myConn; } public void activateObject(Object obj) throws Exception { MyConnection myConn = (MyConnection)obj; logger.info(myConn.getName()); } public void passivateObject(Object obj) throws Exception { MyConnection myConn = (MyConnection)obj; logger.info(myConn.getName()); } public boolean validateObject(Object obj) { MyConnection myConn = (MyConnection)obj; logger.info(myConn.getName()); return myConn.isConnected(); } public void destroyObject(Object obj) throws Exception { MyConnection myConn = (MyConnection)obj; logger.info(myConn.getName()); myConn.close(); } } 最后是一个测试类
package com.googlecode.garbagecan.commons.pool.sample1; import org.apache.commons.pool.ObjectPool; import org.apache.commons.pool.PoolableObjectFactory; import org.apache.commons.pool.impl.StackObjectPool; import org.slf4j.Logger; import org.slf4j.LoggerFactory; public class Test { private static Logger logger = LoggerFactory.getLogger(Test.class); public static void main(String[] args) throws Exception { PoolableObjectFactory factory = new MyConnectionPoolableObjectFactory(); ObjectPool pool = new StackObjectPool(factory); try { logger.info("================================================"); for (int i = 0; i < 10; i++) { MyConnection myConn = (MyConnection)pool.borrowObject(); try { myConn.print(); } catch(Exception ex) { pool.invalidateObject(myConn); } finally { pool.returnObject(myConn); } } logger.info("================================================"); for (int i = 0; i < 10; i++) { MyConnection myConn1 = (MyConnection)pool.borrowObject(); MyConnection myConn2 = (MyConnection)pool.borrowObject(); myConn1.print(); myConn2.print(); pool.returnObject(myConn1); pool.returnObject(myConn2); } } finally { try { pool.close(); } catch (Exception e) { e.printStackTrace(); } } } } 运行测试类，可以看到在第一个循环里虽然循环了10次，一共要了10个MyConnection对象，但是每次返回的都是“conn_1”这个MyConnection对象实例，并且从日志可以看出，makeObject方法只被调用了一次，因此，除了第一次以外，后面的每次申请都是从pool里取出来的。而在第二个循环中，每次申请了两个MyConnection对象实例，从日志可以看到，在第二个循环里也只调用了一次makeObject方法，并且创建的是conn_2对象实例，这是由于conn_1这个对象已经在第一个循环中被创建了出来，此时只是直接拿出来使用了。这里为了好测试，没有在第二个循环中做异常处理，真实情况下应该像第一个循环里的代码类是，在borrowObject和使用pool中对象出现异常时要记得调用invalidateObject方法，并且归还pool中的对象。