HttpClien高并发请求连接池 - PoolingHttpClientConnectionManager（*）

连接池技术作为创建和管理连接的缓冲池技术，目前已广泛用于诸如数据库连接等长连接的维护和管理中，能够有效减少系统的响应时间，节省服务器资源开销。其优势主要有两个：其一是减少创建连接的资源开销，其二是资源的访问控制。连接池管理的对象是长连接，对于HTTP连接是否适用，我们需要首先回顾一下长连接和短连接。

所谓长连接是指客户端与服务器端一旦建立连接以后，可以进行多次数据传输而不需要重新建立连接，而短连接则每次数据传输都需要客户端和服务器端建立一次连接。长连接的优势在于省去了每次数据传输连接建立的时间开销，能够大幅度提高数据传输的速度，对于P2P应用十分适合，但是对于诸如Web网站之类的B2C应用，并发请求量大，每一个用户又不需频繁操作的场景下，维护大量的长连接对服务器无疑是一个巨大的考验。而此时，短连接可能更加适用。但是短连接每次数据传输都需要建立连接，我们知道HTTP协议的传输层协议是TCP协议，TCP连接的建立和释放分别需要进行3次握手和4次挥手，频繁的建立连接即增加了时间开销，同时频繁的创建和销毁Socket同样是对服务器端资源的浪费。所以对于需要频繁发送HTTP请求的应用，需要在客户端使用HTTP长连接。

HTTP连接是无状态的，这样很容易给我们造成HTTP连接是短连接的错觉，实际上HTTP1.1默认即是持久连接，HTTP1.0也可以通过在请求头中设置Connection:keep-alive使得连接为长连接。既然HTTP协议支持长连接，我们就有理由相信HTTP连接同样需要连接池技术来管理和维护连接的建立和销毁。HTTP Client4.0的ThreadSafeClientConnManager实现了HTTP连接的池化管理，其管理连接的基本单位是Route（路由），每个路由上都会维护一定数量的HTTP连接。这里的Route的概念可以理解为客户端机器到目标机器的一条线路，例如使用HttpClient的实现来分别请求 www.163.com 的资源和 www.sina.com 的资源就会产生两个route。缺省条件下对于每个Route，HttpClient仅维护2个连接，总数不超过20个连接，显然对于大多数应用来讲，都是不够用的，可以通过设置HTTP参数进行调整。

两个主机建立连接的过程是很复杂的一个过程，涉及到多个数据包的交换，并且也很耗时间。Http连接需要的三次握手开销很大，这一开销对于比较小的http消息来说更大。但是如果我们直接使用已经建立好的http连接，这样花费就比较小，吞吐率更大。 传统的HttpURLConnection并不支持连接池，如果要实现连接池的机制，还需要自己来管理连接对象。对于网络请求这种底层相对复杂的操作，个人以为如果有可用的其他方案，也没有必要自己去管理连接对象。除了HttpURLConnection，大家肯定还知道HttpClient。一般情况下，普通使用HttpClient已经能满足我们的需求，不过有时候，在我们需要高并发大量的请求网络的时候，还是用“连接池”这样的概念能提升吞吐量。

我们来看下怎么使用 org.apache.httpcomponents.httpclient（版本4.4）提供的连接池来实现我们的高并发网络请求。

使用到的jar包：

org\apache\httpcomponents\httpclient\4.4-beta1\httpclient-4.4-beta1.jar 
org\apache\httpcomponents\httpclient-cache\4.4-beta1\httpclient-cache-4.4-beta1.jar 
org\apache\httpcomponents\httpcore\4.4-beta1\httpcore-4.4-beta1.jar

下面代码实例中主要使用到 PoolingHttpClientConnectionManager

package com.hvgroup.zhuhai10086.jms.utils;
 
import java.io.IOException;
import java.io.InterruptedIOException;
import java.io.UnsupportedEncodingException;
import java.net.UnknownHostException;
import java.util.ArrayList;
import java.util.List;
import java.util.Map;
import java.util.Set;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
 
import javax.net.ssl.SSLException;
import javax.net.ssl.SSLHandshakeException;
 
import org.apache.http.HttpEntity;
import org.apache.http.HttpEntityEnclosingRequest;
import org.apache.http.HttpHost;
import org.apache.http.HttpRequest;
import org.apache.http.NameValuePair;
import org.apache.http.NoHttpResponseException;
import org.apache.http.client.HttpRequestRetryHandler;
import org.apache.http.client.config.RequestConfig;
import org.apache.http.client.entity.UrlEncodedFormEntity;
import org.apache.http.client.methods.CloseableHttpResponse;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.client.methods.HttpRequestBase;
import org.apache.http.client.protocol.HttpClientContext;
import org.apache.http.config.Registry;
import org.apache.http.config.RegistryBuilder;
import org.apache.http.conn.ConnectTimeoutException;
import org.apache.http.conn.routing.HttpRoute;
import org.apache.http.conn.socket.ConnectionSocketFactory;
import org.apache.http.conn.socket.LayeredConnectionSocketFactory;
import org.apache.http.conn.socket.PlainConnectionSocketFactory;
import org.apache.http.conn.ssl.SSLConnectionSocketFactory;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClients;
import org.apache.http.impl.conn.PoolingHttpClientConnectionManager;
import org.apache.http.message.BasicNameValuePair;
import org.apache.http.protocol.HttpContext;
import org.apache.http.util.EntityUtils;
 
/**
 * HttpClient工具类
 * 
 * @return
 * @author SHANHY
 * @create 2015年12月18日
 */
public class HttpClientUtil {
 
    static final int timeOut = 10 * 1000;
 
    private static CloseableHttpClient httpClient = null;
 
    private final static Object syncLock = new Object();
 
    private static void config(HttpRequestBase httpRequestBase) {
        // 设置Header等
        // httpRequestBase.setHeader("User-Agent", "Mozilla/5.0");
        // httpRequestBase
        // .setHeader("Accept",
        // "text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8");
        // httpRequestBase.setHeader("Accept-Language",
        // "zh-CN,zh;q=0.8,en-US;q=0.5,en;q=0.3");// "en-US,en;q=0.5");
        // httpRequestBase.setHeader("Accept-Charset",
        // "ISO-8859-1,utf-8,gbk,gb2312;q=0.7,*;q=0.7");
 
        // 配置请求的超时设置
        RequestConfig requestConfig = RequestConfig.custom()
                .setConnectionRequestTimeout(timeOut)
                .setConnectTimeout(timeOut).setSocketTimeout(timeOut).build();
        httpRequestBase.setConfig(requestConfig);
    }
 
    /**
     * 获取HttpClient对象
     * 
     * @return
     * @author SHANHY
     * @create 2015年12月18日
     */
    public static CloseableHttpClient getHttpClient(String url) {
        String hostname = url.split("/")[2];
        int port = 80;
        if (hostname.contains(":")) {
            String[] arr = hostname.split(":");
            hostname = arr[0];
            port = Integer.parseInt(arr[1]);
        }
        if (httpClient == null) {
            synchronized (syncLock) {
                if (httpClient == null) {
                    httpClient = createHttpClient(200, 40, 100, hostname, port);
                }
            }
        }
        return httpClient;
    }
 
    /**
     * 创建HttpClient对象
     * 
     * @return
     * @author SHANHY
     * @create 2015年12月18日
     */
    public static CloseableHttpClient createHttpClient(int maxTotal,
            int maxPerRoute, int maxRoute, String hostname, int port) {
        ConnectionSocketFactory plainsf = PlainConnectionSocketFactory
                .getSocketFactory();
        LayeredConnectionSocketFactory sslsf = SSLConnectionSocketFactory
                .getSocketFactory();
        Registry<ConnectionSocketFactory> registry = RegistryBuilder
                .<ConnectionSocketFactory> create().register("http", plainsf)
                .register("https", sslsf).build();
        PoolingHttpClientConnectionManager cm = new PoolingHttpClientConnectionManager(
                registry);
        // 将最大连接数增加
        cm.setMaxTotal(maxTotal);
        // 将每个路由基础的连接增加
        cm.setDefaultMaxPerRoute(maxPerRoute);
        HttpHost httpHost = new HttpHost(hostname, port);
        // 将目标主机的最大连接数增加
        cm.setMaxPerRoute(new HttpRoute(httpHost), maxRoute);
 
        // 请求重试处理
        HttpRequestRetryHandler httpRequestRetryHandler = new HttpRequestRetryHandler() {
            public boolean retryRequest(IOException exception,
                    int executionCount, HttpContext context) {
                if (executionCount >= 5) {// 如果已经重试了5次，就放弃
                    return false;
                }
                if (exception instanceof NoHttpResponseException) {// 如果服务器丢掉了连接，那么就重试
                    return true;
                }
                if (exception instanceof SSLHandshakeException) {// 不要重试SSL握手异常
                    return false;
                }
                if (exception instanceof InterruptedIOException) {// 超时
                    return false;
                }
                if (exception instanceof UnknownHostException) {// 目标服务器不可达
                    return false;
                }
                if (exception instanceof ConnectTimeoutException) {// 连接被拒绝
                    return false;
                }
                if (exception instanceof SSLException) {// SSL握手异常
                    return false;
                }
 
                HttpClientContext clientContext = HttpClientContext
                        .adapt(context);
                HttpRequest request = clientContext.getRequest();
                // 如果请求是幂等的，就再次尝试
                if (!(request instanceof HttpEntityEnclosingRequest)) {
                    return true;
                }
                return false;
            }
        };
 
        CloseableHttpClient httpClient = HttpClients.custom()
                .setConnectionManager(cm)
                .setRetryHandler(httpRequestRetryHandler).build();
 
        return httpClient;
    }
 
    private static void setPostParams(HttpPost httpost,
            Map<String, Object> params) {
        List<NameValuePair> nvps = new ArrayList<NameValuePair>();
        Set<String> keySet = params.keySet();
        for (String key : keySet) {
            nvps.add(new BasicNameValuePair(key, params.get(key).toString()));
        }
        try {
            httpost.setEntity(new UrlEncodedFormEntity(nvps, "UTF-8"));
        } catch (UnsupportedEncodingException e) {
            e.printStackTrace();
        }
    }
 
    /**
     * GET请求URL获取内容
     * 
     * @param url
     * @return
     * @author SHANHY
     * @throws IOException 
     * @create 2015年12月18日
     */
    public static String post(String url, Map<String, Object> params) throws IOException {
        HttpPost httppost = new HttpPost(url);
        config(httppost);
        setPostParams(httppost, params);
        CloseableHttpResponse response = null;
        try {
            response = getHttpClient(url).execute(httppost,
                    HttpClientContext.create());
            HttpEntity entity = response.getEntity();
            String result = EntityUtils.toString(entity, "utf-8");
            EntityUtils.consume(entity);
            return result;
        } catch (Exception e) {
//          e.printStackTrace();
            throw e;
        } finally {
            try {
                if (response != null)
                    response.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
 
    /**
     * GET请求URL获取内容
     * 
     * @param url
     * @return
     * @author SHANHY
     * @create 2015年12月18日
     */
    public static String get(String url) {
        HttpGet httpget = new HttpGet(url);
        config(httpget);
        CloseableHttpResponse response = null;
        try {
            response = getHttpClient(url).execute(httpget,
                    HttpClientContext.create());
            HttpEntity entity = response.getEntity();
            String result = EntityUtils.toString(entity, "utf-8");
            EntityUtils.consume(entity);   //关闭HttpEntity是的流，如果手动关闭了InputStream instream = entity.getContent();这个流，也可以不调用这个方法
            return result;
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            try {
                if (response != null)
                    response.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        return null;
    }
 
    public static void main(String[] args) {
        // URL列表数组
        String[] urisToGet = {
                "http://blog.csdn.net/catoop/article/details/38849497",
                "http://blog.csdn.net/catoop/article/details/38849497",
                "http://blog.csdn.net/catoop/article/details/38849497",
                "http://blog.csdn.net/catoop/article/details/38849497",
 
                "http://blog.csdn.net/catoop/article/details/38849497",
                "http://blog.csdn.net/catoop/article/details/38849497",
                "http://blog.csdn.net/catoop/article/details/38849497",
                "http://blog.csdn.net/catoop/article/details/38849497",
 
                "http://blog.csdn.net/catoop/article/details/38849497",
                "http://blog.csdn.net/catoop/article/details/38849497",
                "http://blog.csdn.net/catoop/article/details/38849497",
                "http://blog.csdn.net/catoop/article/details/38849497",
 
                "http://blog.csdn.net/catoop/article/details/38849497",
                "http://blog.csdn.net/catoop/article/details/38849497",
                "http://blog.csdn.net/catoop/article/details/38849497",
                "http://blog.csdn.net/catoop/article/details/38849497",
 
                "http://blog.csdn.net/catoop/article/details/38849497",
                "http://blog.csdn.net/catoop/article/details/38849497",
                "http://blog.csdn.net/catoop/article/details/38849497",
                "http://blog.csdn.net/catoop/article/details/38849497",
 
                "http://blog.csdn.net/catoop/article/details/38849497",
                "http://blog.csdn.net/catoop/article/details/38849497",
                "http://blog.csdn.net/catoop/article/details/38849497",
                "http://blog.csdn.net/catoop/article/details/38849497" };
 
        long start = System.currentTimeMillis();
        try {
            int pagecount = urisToGet.length;
            ExecutorService executors = Executors.newFixedThreadPool(pagecount);
            CountDownLatch countDownLatch = new CountDownLatch(pagecount);
            for (int i = 0; i < pagecount; i++) {
                HttpGet httpget = new HttpGet(urisToGet[i]);
                config(httpget);
                // 启动线程抓取
                executors
                        .execute(new GetRunnable(urisToGet[i], countDownLatch));
            }
            countDownLatch.await();
            executors.shutdown();
        } catch (InterruptedException e) {
            e.printStackTrace();
        } finally {
            System.out.println("线程" + Thread.currentThread().getName() + ","
                    + System.currentTimeMillis() + ", 所有线程已完成，开始进入下一步！");
        }
 
        long end = System.currentTimeMillis();
        System.out.println("consume -> " + (end - start));
    }
 
    static class GetRunnable implements Runnable {
        private CountDownLatch countDownLatch;
        private String url;
 
        public GetRunnable(String url, CountDownLatch countDownLatch) {
            this.url = url;
            this.countDownLatch = countDownLatch;
        }
 
        @Override
        public void run() {
            try {
                System.out.println(HttpClientUtil.get(url));
            } finally {
                countDownLatch.countDown();
            }
        }
    }
}

Post使用方法

// 其中 params 为 Map params
String ret = HttpClientUtil.post(url, params);
            jsonRet = new JSONObject(ret);

一开始我是使用传统的 HttpURLConnection 来做网络请求的，查了很多资料，有不少说 HttpURLConnection 效率高的。可是经过我修改实现方法后，HttpClient 连接池版本的网络请求相对比较稳定。这也说明，我们并不能尽信他人解说，凡事还是要寻找适合自己的方法，真正的解决自己的问题，才是王道。

在使用 HttpURLConnection 的时候，大并发对外做网络请求的时候，前期请求耗时还好，后面耗时越来越高。下面是我之前的实现代码：

    @Deprecated
    protected JSONObject callRestfulOld(String url, Map<String, Object> params) 
    {
        String temp;
        String ret="";
        JSONObject jsonRet=null;
        String sign = generateSign("POST", url, params);// 对参数进行加密签名
        if(sign.isEmpty()) return new JSONObject("{\"ret_code\":-1,\"err_msg\":\"generateSign error\"}");
        params.put("sign", sign);
        try{
            URL u = new URL(url);
            HttpURLConnection conn = (HttpURLConnection)u.openConnection();
            conn.setRequestMethod("POST");
            conn.setConnectTimeout(10000);
            conn.setDoOutput(true);
            conn.setDoInput(true);
            conn.setUseCaches(false);
            StringBuffer param = new StringBuffer();
            for (String key: params.keySet())
            {
                param.append(key).append("=").append(URLEncoder.encode(params.get(key).toString(), "UTF-8")).append("&");
            }
            conn.getOutputStream().write(param.toString().getBytes("UTF-8"));
 
            //System.out.println(param);
            conn.getOutputStream().flush();
            conn.getOutputStream().close();
            InputStreamReader isr = new InputStreamReader(conn.getInputStream());  
            BufferedReader br = new BufferedReader(isr);  
            while((temp = br.readLine()) != null){  
                ret += temp;  
            }     
            br.close();  
            isr.close();
            conn.disconnect();
            //System.out.println(ret);
            jsonRet = new JSONObject(ret);
 
        } catch(java.net.SocketTimeoutException e) {
            //e.printStackTrace();
            jsonRet = new JSONObject("{\"ret_code\":-1,\"err_msg\":\"call restful timeout\"}");
        } catch(Exception e) {
            //e.printStackTrace();
            jsonRet = new JSONObject("{\"ret_code\":-1,\"err_msg\":\"call restful error\"}");
        }
        return jsonRet;
    }

只有一个httpclient的实例，你可以看看CloseableHttpClient和PoolingHttpClientConnectionManager的源码,你会发现httpclient实例通过execute执行get或post获取连接的时候，会通过实例关联的connectionManager的connect()来建立连接，这里的connectionManager是一个连接池的实现, 因此connect方法调用的是PoolingHttpClientConnectionManager重写的实现，这就是一个连接池建立连接的实现，具体还是看源码吧

HttpClient 3.x,4.x都提供了http连接池管理器,当使用了请求连接池管理器（比如PoolingHttpClientConnectionManager）后，HttpClient就可以同时执行多个线程的请求了。

hc3.x和4.x的早期版本,提供了PoolingClientConnectionManager,DefaultHttpClient等类来实现http连接池,但这些类在4.3.x版本之后大部分就已经过时,本文使用4.3.x提供的最新的PoolingHttpClientConnectionManager等类进行http连接池的实现.

废话不多说,下面是全部代码:

public class PoolTest {  
    private static void config(HttpRequestBase httpRequestBase) {  
        httpRequestBase.setHeader("User-Agent", "Mozilla/5.0");  
        httpRequestBase.setHeader("Accept","text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8");  
        httpRequestBase.setHeader("Accept-Language", "zh-CN,zh;q=0.8,en-US;q=0.5,en;q=0.3");//"en-US,en;q=0.5");  
        httpRequestBase.setHeader("Accept-Charset", "ISO-8859-1,utf-8,gbk,gb2312;q=0.7,*;q=0.7");  
          
        // 配置请求的超时设置  
        RequestConfig requestConfig = RequestConfig.custom()  
                .setConnectionRequestTimeout(3000)  
                .setConnectTimeout(3000)  
                .setSocketTimeout(3000)  
                .build();  
        httpRequestBase.setConfig(requestConfig);         
    }  
  
    public static void main(String[] args) {  
        ConnectionSocketFactory plainsf = PlainConnectionSocketFactory.getSocketFactory();  
        LayeredConnectionSocketFactory sslsf = SSLConnectionSocketFactory.getSocketFactory();  
        Registry<ConnectionSocketFactory> registry = RegistryBuilder.<ConnectionSocketFactory>create()  
                .register("http", plainsf)  
                .register("https", sslsf)  
                .build();  
  
        PoolingHttpClientConnectionManager cm = new PoolingHttpClientConnectionManager(registry);  
        // 将最大连接数增加到200  
        cm.setMaxTotal(200);  
        // 将每个路由基础的连接增加到20  
        cm.setDefaultMaxPerRoute(20);  
  
        // 将目标主机的最大连接数增加到50  
        HttpHost localhost = new HttpHost("http://blog.csdn.net/gaolu",80);  
        cm.setMaxPerRoute(new HttpRoute(localhost), 50);  
          
        //请求重试处理  
        HttpRequestRetryHandler httpRequestRetryHandler = new HttpRequestRetryHandler() {  
            public boolean retryRequest(IOException exception,int executionCount, HttpContext context) {  
                if (executionCount >= 5) {// 如果已经重试了5次，就放弃                     
                    return false;  
                }  
                if (exception instanceof NoHttpResponseException) {// 如果服务器丢掉了连接，那么就重试                    
                    return true;  
                }  
                if (exception instanceof SSLHandshakeException) {// 不要重试SSL握手异常                   
                    return false;  
                }                 
                if (exception instanceof InterruptedIOException) {// 超时                   
                    return false;  
                }  
                if (exception instanceof UnknownHostException) {// 目标服务器不可达                   
                    return false;  
                }  
                if (exception instanceof ConnectTimeoutException) {// 连接被拒绝                   
                    return false;  
                }  
                if (exception instanceof SSLException) {// ssl握手异常                    
                    return false;  
                }  
                  
                HttpClientContext clientContext = HttpClientContext.adapt(context);  
                HttpRequest request = clientContext.getRequest();  
                // 如果请求是幂等的，就再次尝试  
                if (!(request instanceof HttpEntityEnclosingRequest)) {                   
                    return true;  
                }  
                return false;  
            }  
        };    
          
        CloseableHttpClient httpClient = HttpClients.custom()  
                .setConnectionManager(cm)  
                .setRetryHandler(httpRequestRetryHandler)  
                .build();  
  
        // URL列表数组  
        String[] urisToGet = {        
                "http://blog.csdn.net/gaolu/article/details/48466059",  
                "http://blog.csdn.net/gaolu/article/details/48243103",  
                "http://blog.csdn.net/gaolu/article/details/47656987",  
                "http://blog.csdn.net/gaolu/article/details/47055029",  
                  
                "http://blog.csdn.net/gaolu/article/details/46400883",  
                "http://blog.csdn.net/gaolu/article/details/46359127",  
                "http://blog.csdn.net/gaolu/article/details/46224821",  
                "http://blog.csdn.net/gaolu/article/details/45305769",  
                  
                "http://blog.csdn.net/gaolu/article/details/43701763",  
                "http://blog.csdn.net/gaolu/article/details/43195449",  
                "http://blog.csdn.net/gaolu/article/details/42915521",  
                "http://blog.csdn.net/gaolu/article/details/41802319",  
                  
                "http://blog.csdn.net/gaolu/article/details/41045233",  
                "http://blog.csdn.net/gaolu/article/details/40395425",  
                "http://blog.csdn.net/gaolu/article/details/40047065",  
                "http://blog.csdn.net/gaolu/article/details/39891877",  
                  
                "http://blog.csdn.net/gaolu/article/details/39499073",  
                "http://blog.csdn.net/gaolu/article/details/39314327",  
                "http://blog.csdn.net/gaolu/article/details/38820809",  
                "http://blog.csdn.net/gaolu/article/details/38439375",  
        };  
          
        long start = System.currentTimeMillis();          
        try {  
            int pagecount = urisToGet.length;  
            ExecutorService executors = Executors.newFixedThreadPool(pagecount);  
            CountDownLatch countDownLatch = new CountDownLatch(pagecount);        
            for(int i = 0; i< pagecount;i++){  
                HttpGet httpget = new HttpGet(urisToGet[i]);  
                config(httpget);  
  
                //启动线程抓取  
                executors.execute(new GetRunnable(httpClient,httpget,countDownLatch));  
            }  
  
            countDownLatch.await();  
            executors.shutdown();  
        } catch (InterruptedException e) {  
            e.printStackTrace();  
        } finally {  
            System.out.println("线程" + Thread.currentThread().getName() + "," + System.currentTimeMillis() + ", 所有线程已完成，开始进入下一步！");  
        }         
          
        long end = System.currentTimeMillis();  
        System.out.println("consume -> " + (end - start));  
    }  
      
    static class GetRunnable implements Runnable {  
        private CountDownLatch countDownLatch;  
        private final CloseableHttpClient httpClient;  
        private final HttpGet httpget;  
          
        public GetRunnable(CloseableHttpClient httpClient, HttpGet httpget, CountDownLatch countDownLatch){  
            this.httpClient = httpClient;  
            this.httpget = httpget;  
              
            this.countDownLatch = countDownLatch;  
        }  
  
        @Override  
        public void run() {  
            CloseableHttpResponse response = null;  
            try {  
                response = httpClient.execute(httpget,HttpClientContext.create());  
                HttpEntity entity = response.getEntity();  
                System.out.println(EntityUtils.toString(entity, "utf-8")) ;  
                EntityUtils.consume(entity);  
            } catch (IOException e) {  
                e.printStackTrace();  
            } finally {  
                countDownLatch.countDown();  
                  
                try {  
                    if(response != null)  
                        response.close();  
                } catch (IOException e) {  
                    e.printStackTrace();  
                }  
            }  
        }  
    }     
}