commons-pool实战之 KeyedPoolableObjectFactory和KeyedObjectPool

有时候，仅仅简单的把池中的所有对象都当成一类对象并不能解决所有问题，有时候我们需要根据一些参数比如key值去查找某些指定的池中对象，比如可以根据一个参数来决定使用池中具体的那一个数据库连接，等等。此时就需要使用KeyedPoolableObjectFactory和KeyedObjectPool接口。

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.sample2; 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KeyedPoolableObjectFactory接口的实现类，提供makeObject, activateObject, passivateObject, validateObject, destroyObject方法。

package com.googlecode.garbagecan.commons.pool.sample2; import org.apache.commons.pool.KeyedPoolableObjectFactory; import org.slf4j.Logger; import org.slf4j.LoggerFactory; public class MyConnectionKeyedPoolableObjectFactory implements KeyedPoolableObjectFactory { private static Logger logger = LoggerFactory.getLogger(MyConnectionKeyedPoolableObjectFactory.class); private static int count = 0; public Object makeObject(Object key) throws Exception { MyConnection myConn = new MyConnection(key.toString()); logger.info(myConn.getName()); myConn.connect(); return myConn; } public void activateObject(Object key, Object obj) throws Exception { MyConnection myConn = (MyConnection)obj; logger.info(myConn.getName()); } public void passivateObject(Object key, Object obj) throws Exception { MyConnection myConn = (MyConnection)obj; logger.info(myConn.getName()); } public boolean validateObject(Object key, Object obj) { MyConnection myConn = (MyConnection)obj; logger.info(myConn.getName()); return myConn.isConnected(); } public void destroyObject(Object key, 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.sample2; import org.apache.commons.pool.KeyedObjectPool; import org.apache.commons.pool.impl.StackKeyedObjectPool; 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 { MyConnectionKeyedPoolableObjectFactory factory = new MyConnectionKeyedPoolableObjectFactory(); KeyedObjectPool pool = new StackKeyedObjectPool(factory); try { logger.info("================================================"); for (int i = 0; i < 10; i++) { String key = "conn_" + i; MyConnection myConn = (MyConnection)pool.borrowObject(key); try { myConn.print(); } catch(Exception ex) { pool.invalidateObject(key, myConn); } finally { pool.returnObject(key, myConn); } } logger.info("================================================"); for (int i = 0; i < 10; i++) { String key = "conn_xxx"; MyConnection myConn = (MyConnection)pool.borrowObject(key); try { myConn.print(); } catch(Exception ex) { pool.invalidateObject(key, myConn); } finally { pool.returnObject(key, myConn); } } } finally { logger.info("Close Pool"); 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次MyConnection对象，每次请求的key都不一样，从conn_0到conn_9，由于使用的是KeyedPoolableObjectFactory和KeyedObjectPool接口，所以返回的10个MyConnection对象实例每个都不一样，并且从日志可以看出makeObject方法被调用了10次。第二个循环里，虽然也是请求了10次MyConnection对象，但是由于每次的key都不一样，所以每次返回的都是同一个MyConnection对象实例，并且从日志可以看出makeObject方法只被调用了一次。