HttpClient的定义

• HttpClient (Http客户端) 是Apache Jakarta Common 下的子项目，可以用来提供高效率、最新的、功能丰富的支持HTTP协议的 客户端编程工具包，其支持HTTP协议最新的版本和建议。
• 说的直白点就是：
  我们可在 java 程序中可通过HttpClient(Http客户端) 这个工具包来构造http请求、发送http请求、接收响应结果、解析(请求)返回的结果。
  （在Java中通过编码的方式来发送http请求）

HttpClient的作用

• 可在 java程序中可通过HttpClient(Http客户端) 这个工具包来构造http请求、发送http请求、接收响应结果、解析(请求)返回的结果。

HttpClient的常用核心API

• HttpClient
• HttpClients
• CloseableHttpClient
• HttpGet
• HttpPost

HttpClient要导入的依赖

<dependency><groupId>org.apache.httpcomponents</groupId><artifactId>httpclient</artifactId><version>4.5.13</version>
</dependency>

HttpClient发送请求的步骤

• 第一步、创建HttpClient对象 (Http客户端对象)。使用该对象可进行“发送请求”。
  （HttpClient (Http客户端类)是一个接口，最后创建是其的实现类）

• 第二步、创建http请求对象。比如说我们要发送一个get请求，我们就要创建一个HttpGet对象；如果要发送post请求，我们就就要构建一个HttpPost对象。

• 第三步、发送请求,接收响应结果。调用HttpClient对象的execute方法发送请求（发送请求），且接收响应结果。

• 第四步、解析返回结果。

  • 获取服务端返回的状态码。
  • 获取客户端返回的数据 (获得响应体，且解析响应体)。

• 第五步、关闭资源。

  (ps : 例子在下面的入门案例中。)

HttpClient入门案例：

HttpClient(Http客户端)发送get请求

@SpringBootTest
public class HttpClientTest {  //Http客户端测试类/**测试通过httpclient(Http客户端)发送GET请求*/@Testpublic void testGet() throws Exception {//创建HttpClient对象 --HttpClien为接口,最后创建出来的为: 与其相关的实现类CloseableHttpClient httpClient = HttpClients.createDefault();//创建Http请求对象 (get请求)HttpGet httpGet = new HttpGet("http://localhost:8080/user/shop/status");//发送请求,接收响应结果CloseableHttpResponse response = httpClient.execute(httpGet);//解析返回结果//获取服务端返回的状态码int statusCode = response.getStatusLine().getStatusCode();System.out.println("服务端返回的状态码为: " +statusCode);//获取服务端(响应)返回的数据 --- 获得响应体HttpEntity entity = response.getEntity();//通过EntityUtils工具类解析“响应体” --- 解析响应体String body = EntityUtils.toString(entity);System.out.println("服务端返回的数据为: "+body);//关闭资源response.close();httpClient.close();}
}

HttpClient(Http客户端)发送post请求

@SpringBootTest
public class HttpClientTest {  //Http客户端测试类/*** 测试类通过HttpClient(Http客户端)发送Post请求*/@Testpublic void testPost() throws Exception {//创建HttpClient对象 --- HttpClient为接口，最后创建出来的为: 与其相关的实现类。CloseableHttpClient httpClient = HttpClients.createDefault();//创建Http请求对象 (Post请求)HttpPost httpPost = new HttpPost("http://localhost:8080/admin/employee/login");//设置post请求的参数 (设置Http请求对象的“参数”)JSONObject jsonObject = new JSONObject();jsonObject.put("username", "admin");jsonObject.put("password", 123456);StringEntity entity = new StringEntity(jsonObject.toString()); //参数为:json字符串entity.setContentEncoding("utf-8");  //设置请求的“编码方式”//请求提交过来的是json格式的数据，这样后端才能正确解析数据entity.setContentType("application/json"); //设置请求的“数据格式”//设置post请求的参数httpPost.setEntity(entity);//发送请求,接收响应结果CloseableHttpResponse reponse = httpClient.execute(httpPost);//解析返回结果int statusCode = reponse.getStatusLine().getStatusCode();   //获取服务端返回的状态码System.out.println("响应码为: "+statusCode);HttpEntity entity1 = reponse.getEntity();String body = EntityUtils.toString(entity1); //使用EntityUtils解析响应体System.out.println("响应数据为: "+body);//关闭资源reponse.close();httpClient.close();}
}

HttpClient工具类 (代码)

package com.sky.utils;import com.alibaba.fastjson.JSONObject;
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.methods.HttpPost;
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.message.BasicNameValuePair;
import org.apache.http.util.EntityUtils;import java.io.IOException;
import java.net.URI;
import java.util.ArrayList;
import java.util.List;
import java.util.Map;/*** Http工具类*/
public class HttpClientUtil {static final  int TIMEOUT_MSEC = 5 * 1000;/*** 发送GET方式请求* @param url* @param paramMap* @return*/public static String doGet(String url,Map<String,String> paramMap){// 创建Httpclient对象CloseableHttpClient httpClient = HttpClients.createDefault();String result = "";CloseableHttpResponse response = null;try{URIBuilder builder = new URIBuilder(url);if(paramMap != null){for (String key : paramMap.keySet()) {builder.addParameter(key,paramMap.get(key));}}URI uri = builder.build();//创建GET请求HttpGet httpGet = new HttpGet(uri);//发送请求response = httpClient.execute(httpGet);//判断响应状态if(response.getStatusLine().getStatusCode() == 200){result = EntityUtils.toString(response.getEntity(),"UTF-8");}}catch (Exception e){e.printStackTrace();}finally {try {response.close();httpClient.close();} catch (IOException e) {e.printStackTrace();}}return result;}/*** 发送POST方式请求* @param url* @param paramMap* @return* @throws IOException*/public static String doPost(String url, Map<String, String> paramMap) throws IOException {// 创建Httpclient对象CloseableHttpClient httpClient = HttpClients.createDefault();CloseableHttpResponse response = null;String resultString = "";try {// 创建Http Post请求HttpPost httpPost = new HttpPost(url);// 创建参数列表if (paramMap != null) {List<NameValuePair> paramList = new ArrayList();for (Map.Entry<String, String> param : paramMap.entrySet()) {paramList.add(new BasicNameValuePair(param.getKey(), param.getValue()));}// 模拟表单UrlEncodedFormEntity entity = new UrlEncodedFormEntity(paramList);httpPost.setEntity(entity);}httpPost.setConfig(builderRequestConfig());// 执行http请求response = httpClient.execute(httpPost);resultString = EntityUtils.toString(response.getEntity(), "UTF-8");} catch (Exception e) {throw e;} finally {try {response.close();} catch (IOException e) {e.printStackTrace();}}return resultString;}/*** 发送POST方式请求* @param url* @param paramMap* @return* @throws IOException*/public static String doPost4Json(String url, Map<String, String> paramMap) throws IOException {// 创建Httpclient对象CloseableHttpClient httpClient = HttpClients.createDefault();CloseableHttpResponse response = null;String resultString = "";try {// 创建Http Post请求HttpPost httpPost = new HttpPost(url);if (paramMap != null) {//构造json格式数据JSONObject jsonObject = new JSONObject();for (Map.Entry<String, String> param : paramMap.entrySet()) {jsonObject.put(param.getKey(),param.getValue());}StringEntity entity = new StringEntity(jsonObject.toString(),"utf-8");//设置请求编码entity.setContentEncoding("utf-8");//设置数据类型entity.setContentType("application/json");httpPost.setEntity(entity);}httpPost.setConfig(builderRequestConfig());// 执行http请求response = httpClient.execute(httpPost);resultString = EntityUtils.toString(response.getEntity(), "UTF-8");} catch (Exception e) {throw e;} finally {try {response.close();} catch (IOException e) {e.printStackTrace();}}return resultString;}private static RequestConfig builderRequestConfig() {return RequestConfig.custom().setConnectTimeout(TIMEOUT_MSEC).setConnectionRequestTimeout(TIMEOUT_MSEC).setSocketTimeout(TIMEOUT_MSEC).build();}
}