一、为什么要用Http连接池

1、降低连接时间的消耗:两个主机建立连接的过程中涉及到多个数据包的交换，Http连接需要的三次握手，http连接的关闭需要四次挥手，使用传统的HttpURLConnection，每次发起Http请求都会重新建立TCP连接，用完就会关闭连接。如果采用连接池则减少了这部分时间损耗。

2、支持更大的并发：如果不采用连接池，每次连接都会打开一个端口，在大并发的情况下系统的端口资源很快就会被用完，导致无法建立新的连接。

二、使用httpClient4.5创建连接池

导入包

<dependency>
    <groupId>org.apache.httpcomponents</groupId>
    <artifactId>httpclient</artifactId>
    <version>4.5.3</version>
</dependency>

1、创建连接池步骤
创建连接池
setMaxTotal设置连接池最大并发连接数
setDefaultMaxPerRoute设置单路由最大并发数
setConnectTimeout使用连接池来管理连接，设置建立连接最大时间
setSocketTimeout设置数据传输过程中数据包之间间隔的最大时间
setProxy设置连接代理（根据需要）

private static CloseableHttpClient httpclient;
    static {
        PoolingHttpClientConnectionManager manager = new PoolingHttpClientConnectionManager();
        manager.setMaxTotal(200); //连接池最大并发连接数
        manager.setDefaultMaxPerRoute(200);//单路由最大并发数,路由是对maxTotal的细分
        httpclient = HttpClients.custom().setConnectionManager(manager).build();
    }

    private static RequestConfig config =RequestConfig.copy(RequestConfig.DEFAULT)
            .setSocketTimeout(10000)
            .setConnectTimeout(5000)
            .setConnectionRequestTimeout(100).build();
           // .setProxy(new HttpHost("127.0.0.1",8888,"http")).build();

三、使用连接池处理Get请求

public static String doGet(String url, Map<String, Object> header)
            throws HttpClientException {
        String ret = "";
        HttpGet get = new HttpGet(url);
        get.setConfig(config);
        get.addHeader(HTTP.CONTENT_ENCODING, "UTF-8");
        CloseableHttpResponse closeableHttpResponse = null;
        try {
            if (header != null) {
                for (Map.Entry<String, Object> entry : header.entrySet()) {
                    get.setHeader(entry.getKey(), entry.getValue().toString());
                }
            }
            closeableHttpResponse = httpclient.execute(get);
            if (closeableHttpResponse.getStatusLine().getStatusCode() == 200) {
                ret = EntityUtils.toString(closeableHttpResponse.getEntity(), "UTF-8");
            } else {
                throw new HttpClientException(
                        "System level error, Code=[" + closeableHttpResponse.getStatusLine().getStatusCode() + "].");
            }
        } catch (ClientProtocolException e) {
            throw new HttpClientException("HttpClient error," + e.getMessage());
        } catch (IOException e) {
            throw new HttpClientException("IO error," + e.getMessage());
        } finally {
            if (closeableHttpResponse != null) {
                try {
                    closeableHttpResponse.close();
                } catch (IOException e) {
                }
            }
        }
        return ret;
    }

四、使用连接池处理Post请求

 public static String doPost(String url, Map<String, Object> params, Map<String, Object> header)
            throws HttpClientException {
        String ret = "";
        HttpPost post = new HttpPost(url);
        post.setConfig(config);
        post.addHeader(HTTP.CONTENT_ENCODING, "UTF-8");
        CloseableHttpResponse closeableHttpResponse = null;
        HttpEntity postEntity = null;
        try {
            if(params!=null) {
                List<NameValuePair> list = new ArrayList<NameValuePair>();
                for (Map.Entry<String, Object> entry : params.entrySet()) {
                    list.add(new BasicNameValuePair(entry.getKey(), entry.getValue().toString()));
                }
                postEntity = new UrlEncodedFormEntity(list);
                post.setEntity(postEntity);
            }

            if (header != null) {
                for (Map.Entry<String, Object> entry : header.entrySet()) {
                    post.setHeader(entry.getKey(), entry.getValue().toString());
                }
            }
            closeableHttpResponse = httpclient.execute(post);
            if (closeableHttpResponse.getStatusLine().getStatusCode() == 200) {
                ret = EntityUtils.toString(closeableHttpResponse.getEntity(), "UTF-8");
            } else {
                throw new HttpClientException(
                        "System level error, Code=[" + closeableHttpResponse.getStatusLine().getStatusCode() + "].");
            }
        } catch (ClientProtocolException e) {
            throw new HttpClientException("HttpClient error," + e.getMessage());
        } catch (IOException e) {
            throw new HttpClientException("IO error," + e.getMessage());
        } finally {
            if(postEntity!=null) {
                try {
                    EntityUtils.consume(postEntity);
                } catch (IOException e) {
                }
            }
            if (closeableHttpResponse != null) {
                try {
                    closeableHttpResponse.close();
                } catch (IOException e) {
                }
            }
        }
        return ret;
    }

五、应用测试

 public static void main(String[] args) {
        String result = null;
        String url ="http://api.superepc.com/vtm/DataFunc?grant_code=XF9JKY0R&is_car_config=0&isCN=1&vinCode=LGBG22E22AY081092";
        try {
         result = doGet("http://123.58.251.183:8080/goods/UserServlet?method=loginMobile&loginname=test1&loginpass=test1");
           String  result1 = doGet(url);
           System.out.println(result);
        } catch (HttpClientException e) {
            e.printStackTrace();
        }


    Map<String,Object> params = new HashMap<String,Object>();
        params.put("method", "loginMobile");
        params.put("loginname", "test1");
        params.put("loginpass", "test1");

        try {
            result = doPost("http://123.58.251.183:8080/goods/UserServlet", params);
        } catch (HttpClientException e) {
            e.printStackTrace();
        }
      System.out.println(result);
}