OkHttp是一款优秀的HTTP框架，它支持get请求和post请求，支持基于Http的文件上传和下载，支持加载图片，支持下载文件透明的GZIP压缩，支持响应缓存避免重复的网络请求，支持使用连接池来降低响应延迟问题。
注:okhttp需要okio库的支持,okio是okhttp的通信基础
官网

安装

• 引入jar包

  implementation 'com.squareup.okhttp3:okhttp:3.14.2'
  

同步请求

• GET请求
  -new OkHttpClient
  -构造Request对象
  -通过前两步中的对象构建Call对象
  -通过 execute() 来提交请求

  OkHttpClient client = new OkHttpClient();
      //Request是OkHttp中访问的请求，Builder是辅助类，Response即OkHttp中的响应。
  String url="http://lilq.cn:8080/quan";
  Request request = new Request.Builder()
          .url(url)
          .build();
  Response response = null;
  try {
      response = client.newCall(request).execute();
      String json = response.body().string();
      //response.body() 不可执行多次 io读取完流关闭
      System.out.println(json);
  } catch (IOException e) {
      e.printStackTrace();
  }
  

• POST请求
  POST与GET相比，就是在构造Request对象时，需要多构造一个RequestBody对象，用它来携带我们要提交的数据。在构造 RequestBody 需要指定MediaType，用于描述请求/响应 body 的内容类型

  OkHttpClient client = new OkHttpClient();
  String url = "http://lilq.cn:8080/quan";
  String json = "{\"name\":\"Http权威指南\"}";
  //设置请求体 MediaType指定媒体类型
  RequestBody body = RequestBody.create(MediaType.parse("application/json; charset=utf-8"),json);
  Request request = new Request.Builder()
          .url(url)
          .post(body)//等同 method("POST",body) 请求方法需要全部大写
          .build();
  Response response = null;
  try {
      response = client.newCall(request).execute();
      String resJson = response.body().string();
      System.out.println(resJson);
  } catch (IOException e) {
      e.printStackTrace();
  }
  

异步处理

异步处理需要通过Call#enqueue(Callback)方法来提交异步请求

• GET请求

  OkHttpClient client = new OkHttpClient();
  String url = "http://lilq.cn:8080/quan";
  Request request = new Request.Builder()
          .url(url)
          .build();
  //加入队列
  client.newCall(request).enqueue(new Callback() {
      @Override
      public void onFailure(Call call, IOException e) {
          System.out.println(e);
      }
      @Override
      public void onResponse(Call call, Response response) throws IOException {
          String resJson = response.body().string();
          System.out.println(resJson);
      }
  });
  

• POST请求

  OkHttpClient client = new OkHttpClient();
  String url = "http://lilq.cn:8080/quan";
  String json = "{\"name\":\"JAVA核心思想\"}";
  RequestBody requestBody = RequestBody.create(MediaType.parse("application/json;charset=utf-8"),json);
  Request request = new Request.Builder()
          .method("POST",requestBody)
          .url(url)
          .build();
  client.newCall(request).enqueue(new Callback() {
      @Override
      public void onFailure(Call call, IOException e) {
          System.out.println(e);
      }
      @Override
      public void onResponse(Call call, Response response) throws IOException {
          String resJson = response.body().string();
          System.out.println(resJson);
      }
  });