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;并通知PoolableObjectFactory完成相应的工作;
ObjectPoolFactory用于大量生成相同类型和设置的ObjectPool。
PoolableObjectFactory用于管理被池化的对象的产生、激活、挂起、校验和销毁;
相应地,使用Pool组件的过程,也大体可以划分成“创立PoolableObjectFactory”、“使用ObjectPool”和可选的“利用ObjectPoolFactory”三种动作。
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。