common-pool2 学习：thrift连接池的另一种实现

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thrift客户端连接池。如果不想重造轮子，可以直接在apache开源项目commons-pool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<TProtocol> {

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<TProtocol> 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<TProtocol> 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<TProtocol> 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<TProtocol> pooledObject) throws TTransportException {
passivateObject(pooledObject);
pooledObject.markAbandoned();
}

/**
* 验证对象有效性
*
* @param p
* @return
*/
@Override
public boolean validateObject(PooledObject<TProtocol> 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 AutoClearGenericObjectPool<T> extends GenericObjectPool<T> {

public AutoClearGenericObjectPool(PooledObjectFactory<T> factory) {
super(factory);
}

public AutoClearGenericObjectPool(PooledObjectFactory<T> 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<TProtocol> pool = new AutoClearGenericObjectPool<>(
new TProtocolFactory("127.0.0.1", 13041, true), poolConfig);

List<TProtocol> 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@1e9e725a
org.apache.thrift.protocol.TCompactProtocol@516be40f
org.apache.thrift.protocol.TCompactProtocol@3c0a50da
org.apache.thrift.protocol.TCompactProtocol@3c0a50da
org.apache.thrift.protocol.TCompactProtocol@646be2c3
org.apache.thrift.protocol.TCompactProtocol@646be2c3
org.apache.thrift.protocol.TCompactProtocol@797badd3
org.apache.thrift.protocol.TCompactProtocol@797badd3
org.apache.thrift.protocol.TCompactProtocol@77be656f
active:5,idea:1
active:4,idea:2
active:3,idea:0
active:2,idea:1
active:1,idea:0
------------------------
org.apache.thrift.protocol.TCompactProtocol@221af3c0
org.apache.thrift.protocol.TCompactProtocol@62bd765
org.apache.thrift.protocol.TCompactProtocol@23a5fd2
org.apache.thrift.protocol.TCompactProtocol@78a2da20
org.apache.thrift.protocol.TCompactProtocol@78a2da20
org.apache.thrift.protocol.TCompactProtocol@dd3b207
org.apache.thrift.protocol.TCompactProtocol@dd3b207
org.apache.thrift.protocol.TCompactProtocol@551bdc27
org.apache.thrift.protocol.TCompactProtocol@551bdc27
org.apache.thrift.protocol.TCompactProtocol@58fdd99
active:5,idea:1
active:4,idea:2
active:3,idea:0
active:2,idea:1
active:1,idea:0

Process 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。