工具类——HttpClientUtil带连接池的实现

为什么要使用连接池：

1、降低延迟：如果不采用连接池，每次连接发起Http请求的时候都会重新建立TCP连接(经历3次握手)，用完就会关闭连接(4次挥手)，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。

话不多说，直接上代码，就是个工具类，之前提供了代码，这次是加入了连接池的代码。

package xxx;

import org.apache.http.HttpEntity;
import org.apache.http.NameValuePair;
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.utils.URIBuilder;
import org.apache.http.entity.StringEntity;
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.util.EntityUtils;

import java.io.IOException;
import java.io.UnsupportedEncodingException;
import java.net.URISyntaxException;
import java.util.ArrayList;
import java.util.Map;

public class HttpClientUtil {
    private static PoolingHttpClientConnectionManager cm;
    private static String EMPTY_STR = "";
    private static String UTF_8 = "UTF-8";

    private static void init() {
        if (cm == null) {
            cm = new PoolingHttpClientConnectionManager();
            // 整个连接池最大连接数
            cm.setMaxTotal(50);
            // 每路由最大连接数，默认值是2
            cm.setDefaultMaxPerRoute(5);
        }
    }

    /**
     * 通过连接池获取HttpClient
     *
     * @return
     */
    private static CloseableHttpClient getHttpClient() {
        init();
        return HttpClients.custom().setConnectionManager(cm).build();
    }

    /**
     * @param url
     * @return
     */
    public static String httpGetRequest(String url) {
        HttpGet httpGet = new HttpGet(url);
        return getResult(httpGet);
    }

    public static String httpGetRequest(String url, Map params) throws URISyntaxException {
        URIBuilder ub = new URIBuilder();
        ub.setPath(url);
        ArrayList pairs = covertParams2NVPS(params);
        ub.setParameters(pairs);
        HttpGet httpGet = new HttpGet(ub.build());
        return getResult(httpGet);
    }

    public static String httpGetRequest(String url, Map headers, Map params)
            throws URISyntaxException {
        URIBuilder ub = new URIBuilder();
        ub.setPath(url);
        ArrayList pairs = covertParams2NVPS(params);
        ub.setParameters(pairs);
        HttpGet httpGet = new HttpGet(ub.build());
        for (Map.Entry param : headers.entrySet()) {
            httpGet.addHeader(param.getKey(), String.valueOf(param.getValue()));
        }
        return getResult(httpGet);
    }

    public static String httpPostRequest(String url) {
        HttpPost httpPost = new HttpPost(url);
        return getResult(httpPost);
    }

    public static String httpPostRequest(String url,String json) {
        HttpPost httpPost = new HttpPost(url);
        StringEntity entity = new StringEntity(json,"utf-8");//解决中文乱码问题
        entity.setContentEncoding("UTF-8");
        entity.setContentType("application/json");
        httpPost.setEntity(entity);
        return getResult(httpPost);
    }

    public static String httpPostRequest(String url, Map params) throws UnsupportedEncodingException {
        HttpPost httpPost = new HttpPost(url);
        ArrayList pairs = covertParams2NVPS(params);
        httpPost.setEntity(new UrlEncodedFormEntity(pairs, UTF_8));
        return getResult(httpPost);
    }

    public static String httpPostRequest(String url, Map headers, Map params)
            throws UnsupportedEncodingException {
        HttpPost httpPost = new HttpPost(url);
        for (Map.Entry param : headers.entrySet()) {
            httpPost.addHeader(param.getKey(), String.valueOf(param.getValue()));
        }
        ArrayList pairs = covertParams2NVPS(params);
        httpPost.setEntity(new UrlEncodedFormEntity(pairs, UTF_8));

        return getResult(httpPost);
    }

    private static ArrayList covertParams2NVPS(Map params) {
        ArrayList pairs = new ArrayList();
        for (Map.Entry param : params.entrySet()) {
            pairs.add(new BasicNameValuePair(param.getKey(), String.valueOf(param.getValue())));
        }
        return pairs;
    }

    /**
     * 处理Http请求
     */
    private static String getResult(HttpRequestBase request) {
        // CloseableHttpClient httpClient = HttpClients.createDefault();
        CloseableHttpClient httpClient = getHttpClient();
        try {
            CloseableHttpResponse response = httpClient.execute(request);
            // response.getStatusLine().getStatusCode();
            HttpEntity entity = response.getEntity();
            if (entity != null) {
                // long len = entity.getContentLength();// -1 表示长度未知
                String result = EntityUtils.toString(entity);
                response.close();
                // httpClient.close();
                return result;
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
        return EMPTY_STR;
    }

}