值 得一说的是，对于基于TCP的HTTP协议，关闭TCP连接的是Server端，这样，Server端会进入TIME_WAIT状态，可 想而知，对于访 问量大的Web Server，会存在大量的TIME_WAIT状态，假如server一秒钟接收1000个请求，那么就会积压 240*1000=240，000个 TIME_WAIT的记录，维护这些状态给Server带来负担。当然现代操作系统都会用快速的查找算法来管理这些 TIME_WAIT，所以对于新的 TCP连接请求，判断是否hit中一个TIME_WAIT不会太费时间，但是有这么多状态要维护总是不好。
HTTP协议1.1版规定default行为是Keep-Alive，也就是会重用TCP连接传输多个 request/response，一个主要原因就是发现了这个问题。  

public class HttpApacheClient {private static class SingletonHandler{private static HttpApacheClient singleton = new HttpApacheClient();}private HttpApacheClient(){}public static HttpApacheClient getInstance(){return SingletonHandler.singleton;}private static Logger logger = LoggerFactory.getLogger(HttpApacheClient.class);private final HttpClientConnectionManager manager = builderPoolConnectionManager() ;  //定义连接池管理变量ResponseHandler<String> responseHandler = new ResponseHandler<String>() {@Overridepublic String handleResponse(final HttpResponse response)throws ClientProtocolException, IOException {int status = response.getStatusLine().getStatusCode();if (status >= 200 && status < 300) {HttpEntity entity = response.getEntity();if (entity == null) throw new BusinessException(RESULT_LOG_ERROR);String content =  EntityUtils.toString(entity);logger.info("the log back :"+content);JSONObject jsonObject = JSON.parseObject(content);Integer returnStatus = (Integer)jsonObject.get("status");if (returnStatus !=200) throw new BusinessException(RESULT_LOG_ERROR,content);return content;} else {throw new ClientProtocolException("Unexpected response status: " + status);}}};public HttpClientConnectionManager builderPoolConnectionManager(){final SSLContext context = SSLContexts.createSystemDefault();final HostnameVerifier verifier = new DefaultHostnameVerifier() ;//自定义注册器，既可以发送http请求，也可以发送https请求final Registry<ConnectionSocketFactory> register = RegistryBuilder.<ConnectionSocketFactory>create().register("http" , PlainConnectionSocketFactory.INSTANCE).register("https" , new SSLConnectionSocketFactory(context ,verifier)).build() ;PoolingHttpClientConnectionManager poolingHttpClientConnectionManager = new PoolingHttpClientConnectionManager(register);poolingHttpClientConnectionManager.setMaxTotal(200);  //设置连接池的最大连接数poolingHttpClientConnectionManager.setDefaultMaxPerRoute(poolingHttpClientConnectionManager.getMaxTotal());  //一个路由的最大连接数return poolingHttpClientConnectionManager ;}public HttpClient buildHttpClient(){RequestConfig config = RequestConfig.custom().setConnectionRequestTimeout(3000)  //从池中获取请求的时间.setConnectTimeout(2000)   //连接到服务器的时间.setSocketTimeout(5000).build(); //读取信息时间
CloseableHttpClient build = HttpClients.custom().setRetryHandler(DefaultHttpRequestRetryHandler.INSTANCE).setDefaultRequestConfig(config).setConnectionManagerShared(true).setConnectionManager(manager).build();return build ;}public static String postJson(String url, List<NameValuePair> params) throws Exception {String urlHead = (String) BeanHelper.getConfig("url");url = urlHead+url;logger.info("url "+url+";"+params);HttpApacheClient utils = getInstance();HttpClient httpClient = null;HttpPost httpPost = null;try {httpClient = utils.buildHttpClient();httpPost = new HttpPost(url);httpPost.setEntity(new UrlEncodedFormEntity(params,"UTF-8"));httpPost.setHeader("Content-type", "application/x-www-form-urlencoded");return httpClient.execute(httpPost, utils.responseHandler);}catch (Exception e){if (httpPost!=null) httpPost.abort();//异常时 关闭连接throw  e;}}}
}