HttpClient工具类（使用连接池）

HttpClient工具类（使用连接池）

HttpClient简介

(~~~~~)HTTP 协议可能是现在 Internet 上使用得最多、最重要的协议了，越来越多的 Java 应用程序需要直接通过 HTTP 协议来访问网络资源。虽然在 JDK 的 java net包中已经提供了访问 HTTP 协议的基本功能，但是对于大部分应用程序来说，JDK 库本身提供的功能还不够丰富和灵活。HttpClient 是 Apache Jakarta Common 下的子项目，用来提供高效的、最新的、功能丰富的支持 HTTP 协议的客户端编程工具包，并且它支持 HTTP 协议最新的版本和建议。

(~~~~~)HTTP和浏览器有点像，但却不是浏览器。很多人觉得既然HttpClient是一个HTTP客户端编程工具，很多人把他当做浏览器来理解，但是其实HttpClient不是浏览器，它是一个HTTP通信库，因此它只提供一个通用浏览器应用程序所期望的功能子集，最根本的区别是HttpClient中没有用户界面，浏览器需要一个渲染引擎来显示页面，并解释用户输入，例如鼠标点击显示页面上的某处，有一个布局引擎，计算如何显示HTML页面，包括级联样式表和图像。javascript解释器运行嵌入HTML页面或从HTML页面引用的javascript代码。来自用户界面的事件被传递到javascript解释器进行处理。除此之外，还有用于插件的接口，可以处理Applet，嵌入式媒体对象（如pdf文件，Quicktime电影和Flash动画）或ActiveX控件（可以执行任何操作）。HttpClient只能以编程的方式通过其API用于传输和接受HTTP消息

HttpClient主要功能

• 实现了所有 HTTP 的方法（GET、POST、PUT、HEAD、DELETE、HEAD、OPTIONS 等）
• 支持 HTTPS 协议
• 支持代理服务器（Nginx等）等
• 支持自动（跳转）转向

简单使用

引入相关依赖

<!-- https://mvnrepository.com/artifact/org.apache.httpcomponents/httpclient -->
<dependency>
    <groupId>org.apache.httpcomponents</groupId>
    <artifactId>httpclient</artifactId>
    <version>4.5.5</version>
</dependency>

这里提醒一点：springboot中也已经整合有HttpClient依赖，也可以另外引入依赖

单独发送Get请求

/**
     * 向指定URL发送GET方法的请求
     *
     * @param url
     *            发送请求的URL
     * @param param
     *            请求参数，请求参数应该是 name1=value1&name2=value2 的形式。
     * @return URL 所代表远程资源的响应结果
     */
    public static String sendGet(String url, String param) {
        String result = "";
        BufferedReader in = null;
        try {
            String urlNameString = url + "?" + param;
            URL realUrl = new URL(urlNameString);
            // 打开和URL之间的连接
            URLConnection connection = realUrl.openConnection();
            // 设置通用的请求属性
            connection.setRequestProperty("accept", "*/*");
            connection.setRequestProperty("connection", "Keep-Alive");
            connection.setRequestProperty("user-agent",
                    "Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1;SV1)");
            // 建立实际的连接
            connection.connect();
            // 获取所有响应头字段
            Map<String, List<String>> map = connection.getHeaderFields();
            // 遍历所有的响应头字段
            for (String key : map.keySet()) {
                System.out.println(key + "--->" + map.get(key));
            }
            // 定义 BufferedReader输入流来读取URL的响应
            in = new BufferedReader(new InputStreamReader(
                    connection.getInputStream()));
            String line;
            while ((line = in.readLine()) != null) {
                result += line;
            }
        } catch (Exception e) {
            System.out.println("发送GET请求出现异常！" + e);
            e.printStackTrace();
        }
        // 使用finally块来关闭输入流
        finally {
            try {
                if (in != null) {
                    in.close();
                }
            } catch (Exception e2) {
                e2.printStackTrace();
            }
        }
        return result;
    }

单独发送Post请求

---

post请求有两种方式传参，一种是普通参数，一种是对象参数

/**
     * 向指定 URL 发送POST方法的请求
     *
     * @param url
     *            发送请求的 URL
     * @param param
     *            请求参数，请求参数应该是 name1=value1&name2=value2 的形式。
     * @return 所代表远程资源的响应结果
     */
    public static String sendPost(String url, String param) {
        PrintWriter out = null;
        BufferedReader in = null;
        String result = "";
        try {
            URL realUrl = new URL(url);
            // 打开和URL之间的连接
            URLConnection conn = realUrl.openConnection();
            // 设置通用的请求属性
            conn.setRequestProperty("accept", "*/*");
            conn.setRequestProperty("connection", "Keep-Alive");
            conn.setRequestProperty("user-agent",
                    "Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1;SV1)");
            // 发送POST请求必须设置如下两行
            conn.setDoOutput(true);
            conn.setDoInput(true);
            // 获取URLConnection对象对应的输出流
            out = new PrintWriter(conn.getOutputStream());
            // 发送请求参数
            out.print(param);
            // flush输出流的缓冲
            out.flush();
            // 定义BufferedReader输入流来读取URL的响应
            in = new BufferedReader(
                    new InputStreamReader(conn.getInputStream()));
            String line;
            while ((line = in.readLine()) != null) {
                result += line;
            }
        } catch (Exception e) {
            System.out.println("发送 POST 请求出现异常！"+e);
            e.printStackTrace();
        }
        //使用finally块来关闭输出流、输入流
        finally{
            try{
                if(out!=null){
                    out.close();
                }
                if(in!=null){
                    in.close();
                }
            }
            catch(IOException ex){
                ex.printStackTrace();
            }
        }
        return result;
    }

使用HttpClient连接池，优化连接

---

• 这里整合在springboot :2.2.6.RELEASE 版本

package com.vx.music.http;

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.*;
import java.net.URISyntaxException;
import java.net.URL;
import java.net.URLConnection;
import java.util.ArrayList;
import java.util.List;
import java.util.Map;

public class HttpClientApiUtils {
    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(100);
            // 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<String, Object> params) throws URISyntaxException {
        URIBuilder ub = new URIBuilder(url);
        ArrayList<NameValuePair> pairs = covertParams2NVPS(params);
        ub.setParameters(pairs);
        HttpGet httpGet = new HttpGet(ub.build());
        return getResult(httpGet);
    }

    public static String httpGetRequest(String url, Map<String, Object> headers, Map<String, Object> params)
            throws URISyntaxException {
        URIBuilder ub = new URIBuilder();
        ub.setPath(url);
        ArrayList<NameValuePair> pairs = covertParams2NVPS(params);
        ub.setParameters(pairs);
        HttpGet httpGet = new HttpGet(ub.build());
        for (Map.Entry<String, Object> 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<String, Object> params) throws UnsupportedEncodingException {
        HttpPost httpPost = new HttpPost(url);
        ArrayList<NameValuePair> pairs = covertParams2NVPS(params);
        httpPost.setEntity(new UrlEncodedFormEntity(pairs, UTF_8));
        return getResult(httpPost);
    }

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

        return getResult(httpPost);
    }

    private static ArrayList<NameValuePair> covertParams2NVPS(Map<String, Object> params) {
        ArrayList<NameValuePair> pairs = new ArrayList<NameValuePair>();
        for (Map.Entry<String, Object> 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;
    }
}

HttpClient4.X发送Get请求的参数拼接

使用httpClient发送get请求时，请求参数可以以？key=val&key1=val1的拼接到url后面。
但是请求参数较多时，这种方法比较麻烦，也不太优雅；研究了一下发现HttpClient4.X本身
是支持处理参数的。

1. 使用 URIBuilder来构建请求URI

import com.google.common.collect.Lists;
import org.apache.http.Consts;
import org.apache.http.HttpEntity;
import org.apache.http.HttpStatus;
import org.apache.http.NameValuePair;
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.utils.URIBuilder;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClients;
import org.apache.http.message.BasicNameValuePair;
import org.apache.http.util.EntityUtils;

    private HttpGet buildHttpGet(String url, Map<String, String> para)
            throws URISyntaxException {
        URIBuilder builder = new URIBuilder(url);
        Set<String> set = para.keySet();
        for(String key: set){
            builder.setParameter(key, para.get(key));
        }
        HttpGet request = new HttpGet(builder.build());
        RequestConfig requestConfig = RequestConfig.custom()
                .setSocketTimeout(6000)
                .setConnectTimeout(6000)
                .setConnectionRequestTimeout(6000).build();
        request.setConfig(requestConfig);
        System.out.println(request.getURI().toString());
        return request;
    }

2. 使用 NameValuePair 来拼接URI

List<NameValuePair> params = Lists.newArrayList();
params.add(new BasicNameValuePair("cityEname", "henan"));
String str = "";
//转换为键值对
str = EntityUtils.toString(new UrlEncodedFormEntity(params, Consts.UTF_8));
System.out.println(str);
HttpGet httpGet = new HttpGet(url + "?" + str);

3. 根据 HttpGet反向获取键值对列表

HttpGet request = new HttpGet("http://example.com/?var=1&var=2");
URIBuilder newBuilder = new URIBuilder(request.getURI());
//获取键值对列表
List<NameValuePair> params = newBuilder.getQueryParams();
//转换为键值对字符串
String str = EntityUtils.toString(new UrlEncodedFormEntity(params, Consts.UTF_8));

其它

其它更多其它详细使用：

https://github.com/Arronlong/httpclientutil