两个主机建立连接的过程是非常复杂的一个过程，涉及到多个数据包的交换，而且也非常耗时间。Http连接须要的三次握手开销非常大，这一开销对于比較小的http消息来说更大。但是假设我们直接使用已经建立好的http连接。这样花费就比較小。吞吐率更大。

传统的HttpURLConnection并不支持连接池。假设要实现连接池的机制，还须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。个人以为假设有可用的其它方案，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。普通情况下，普通使用HttpClient已经能满足我们的需求，只是有时候。在我们须要高并发大量的请求网络的时候，还是用“连接池”这种概念能提升吞吐量。

我们来看下怎么使用 org.apache.httpcomponents.httpclient（版本号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

以下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
      
        registry = RegistryBuilder                .
       
         create().register("http", plainsf)                .register("https", sslsf).build();        PoolingHttpClientConnectionManager cm = new PoolingHttpClientConnectionManager(                registry);        // 将最大连接数添加        cm.setMaxTotal(maxTotal);        // 将每一个路由基础的连接添加        cm.setDefaultMaxPerRoute(maxPerRoute);        HttpHost httpHost = new HttpHost(hostname, port);        // 将目标主机的最大连接数添加        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) {
     // 假设已经重试了5次，就放弃                    return false;                }                if (exception instanceof NoHttpResponseException) {
     // 假设server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server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();                // 假设请求是幂等的，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
        
          params) {        List
         
           nvps = new ArrayList
          
           ();        Set
           
             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
            
              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); 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() + ", 全部线程已完毕。開始进入下一步！
            
           
          
         
        
       
      

"

); } 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用法

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

一開始我是使用传统的 HttpURLConnection 来做网络请求的。查了非常多资料，有不少说 HttpURLConnection 效率高的。但是经过我改动实现方法后，HttpClient 连接池版本号的网络请求相对照较稳定。

这也说明，我们并不请尽信他人讲解，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。以下是我之前的实现代码：

@Deprecated    protected JSONObject callRestfulOld(String url, Map
      
        params)     {        String temp;        String ret="";        JSONObject jsonRet=null;        String sign = generateSign("POST", url, params);// 对參数进行加密签名        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;    }
      

（完）