对象池是一种很实用的技术，经典的例子就是数据库连接池。去年曾经从零开始写过一个。如果不想重造轮子，可以直接在apache开源项目的基础上开发。
步骤：
一、定义对象工厂
package test.cn.mwee.service.paidui.pool;import org.apache.commons.pool2.BasePooledObjectFactory;import org.apache.commons.pool2.PooledObject;import org.apache.commons.pool2.impl.DefaultPooledObject;import org.apache.thrift.protocol.TCompactProtocol;import org.apache.thrift.protocol.TProtocol;import org.apache.thrift.transport.TFramedTransport;import org.apache.thrift.transport.TSocket;import org.apache.thrift.transport.TTransport;import org.apache.thrift.transport.TTransportException;public class TProtocolFactory extends BasePooledObjectFactory{ private String host; private int port; private boolean keepAlive = true; public TProtocolFactory(String host, int port, boolean keepAlive) { this.host = host; this.port = port; this.keepAlive = keepAlive; } @Override public TProtocol create() throws TTransportException { TSocket tSocket = new TSocket(host, port); TTransport tTransport = new TFramedTransport(tSocket); tTransport.open(); return new TCompactProtocol(tTransport); } @Override public PooledObject wrap(TProtocol protocol) { return new DefaultPooledObject<>(protocol); } /** * 对象钝化(即：从激活状态转入非激活状态，returnObject时触发） * * @param pooledObject * @throws TTransportException */ @Override public void passivateObject(PooledObject pooledObject) throws TTransportException { if (!keepAlive) { pooledObject.getObject().getTransport().flush(); pooledObject.getObject().getTransport().close(); } } /** * 对象激活(borrowObject时触发） * * @param pooledObject * @throws TTransportException */ @Override public void activateObject(PooledObject pooledObject) throws TTransportException { if (!pooledObject.getObject().getTransport().isOpen()) { pooledObject.getObject().getTransport().open(); } } /** * 对象销毁(clear时会触发） * @param pooledObject * @throws TTransportException */ @Override public void destroyObject(PooledObject pooledObject) throws TTransportException { passivateObject(pooledObject); pooledObject.markAbandoned(); } /** * 验证对象有效性 * * @param p * @return */ @Override public boolean validateObject(PooledObject p) { if (p.getObject() != null) { if (p.getObject().getTransport().isOpen()) { return true; } try { p.getObject().getTransport().open(); return true; } catch (TTransportException e) { e.printStackTrace(); } } return false; }}
有二个关键的方法，需要重写：activateObject（对象激活） 及 passivateObject(对象钝化)
二、定义对象池
package test.cn.mwee.service.paidui.pool;import org.apache.commons.pool2.PooledObjectFactory;import org.apache.commons.pool2.impl.GenericObjectPool;import org.apache.commons.pool2.impl.GenericObjectPoolConfig;/** * Created by yangjunming on 6/7/16. */public class AutoClearGenericObjectPoolextends GenericObjectPool { public AutoClearGenericObjectPool(PooledObjectFactory factory) { super(factory); } public AutoClearGenericObjectPool(PooledObjectFactory factory, GenericObjectPoolConfig config) { super(factory, config); } @Override public void returnObject(T obj) { super.returnObject(obj); //空闲数>=激活数时，清理掉空闲连接 if (getNumIdle() >= getNumActive()) { clear(); } }}
common-pools提供了对象池的默认实现：GenericObjectPool 但是该对象池中，对于处于空闲的对象，需要手动调用clear来释放空闲对象，如果希望改变这一行为，可以自己派生自己的子类，重写returnObject方法，上面的代码中，每次归还对象时，如果空闲的对象比激活的对象还要多（即：一半以上的对象都在打酱油），则调用clear方法。
三、使用示例：
package test.cn.mwee.service.paidui.pool;import org.apache.commons.pool2.ObjectPool;import org.apache.commons.pool2.impl.GenericObjectPoolConfig;import org.apache.thrift.protocol.TProtocol;import java.util.ArrayList;import java.util.List;import java.util.Random;/** * thrift 连接池测试 */public class ProtocolPoolTest { public static void main(String[] args) throws Exception { GenericObjectPoolConfig poolConfig = new GenericObjectPoolConfig(); poolConfig.setMaxTotal(10); poolConfig.setMinIdle(1); poolConfig.setTestOnBorrow(true); ObjectPool pool = new AutoClearGenericObjectPool<>( new TProtocolFactory("127.0.0.1", 13041, true), poolConfig); List list = new ArrayList<>(); for (int i = 1; i <= 10; i++) { TProtocol protocol = pool.borrowObject(); System.out.println(protocol.toString()); if (i % 2 == 0) { //10个连接中，将偶数归还 pool.returnObject(protocol); } else { list.add(protocol); } } Random rnd = new Random(); while (true) { System.out.println(String.format("active:%d,idea:%d", pool.getNumActive(), pool.getNumIdle())); Thread.sleep(5000); //每次还一个 if (list.size() > 0) { int i = rnd.nextInt(list.size()); pool.returnObject(list.get(i)); list.remove(i); } //直到全部还完 if (pool.getNumActive() <= 0) { break; } } System.out.println("------------------------"); list.clear(); //连接池为空，测试是否能重新创建新连接 for (int i = 1; i <= 10; i++) { TProtocol protocol = pool.borrowObject(); System.out.println(protocol.toString()); if (i % 2 == 0) { pool.returnObject(protocol); } else { list.add(protocol); } } while (true) { System.out.println(String.format("active:%d,idea:%d", pool.getNumActive(), pool.getNumIdle())); Thread.sleep(5000); if (list.size() > 0) { int i = rnd.nextInt(list.size()); pool.returnObject(list.get(i)); list.remove(i); } if (pool.getNumActive() <= 0) { pool.close(); break; } } }} 注：需要从对象池取一个对象时，调用borrowObject（背后会调用activeObject激活对象），类似的，对象使用完之后，需要调用returnObject将对象放回对象池（背后会调用passivateObject使对象钝化）
输出：
org.apache.thrift.protocol.TCompactProtocol@146044d7
org.apache.thrift.protocol.TCompactProtocol@1e9e725aorg.apache.thrift.protocol.TCompactProtocol@516be40forg.apache.thrift.protocol.TCompactProtocol@3c0a50daorg.apache.thrift.protocol.TCompactProtocol@3c0a50daorg.apache.thrift.protocol.TCompactProtocol@646be2c3org.apache.thrift.protocol.TCompactProtocol@646be2c3org.apache.thrift.protocol.TCompactProtocol@797badd3org.apache.thrift.protocol.TCompactProtocol@797badd3org.apache.thrift.protocol.TCompactProtocol@77be656factive:5,idea:1active:4,idea:2active:3,idea:0active:2,idea:1active:1,idea:0------------------------org.apache.thrift.protocol.TCompactProtocol@221af3c0org.apache.thrift.protocol.TCompactProtocol@62bd765org.apache.thrift.protocol.TCompactProtocol@23a5fd2org.apache.thrift.protocol.TCompactProtocol@78a2da20org.apache.thrift.protocol.TCompactProtocol@78a2da20org.apache.thrift.protocol.TCompactProtocol@dd3b207org.apache.thrift.protocol.TCompactProtocol@dd3b207org.apache.thrift.protocol.TCompactProtocol@551bdc27org.apache.thrift.protocol.TCompactProtocol@551bdc27org.apache.thrift.protocol.TCompactProtocol@58fdd99active:5,idea:1active:4,idea:2active:3,idea:0active:2,idea:1active:1,idea:0Process finished with exit code 0
从输出上看，归还对象后，再次取出时，并没有创建新对象，而是直接使用了对象池中已经空闲的对象。当对象池中的所有对象都归还变成空闲并被clear后，再次从对象池中借对象时，会重新创建对象。