okhttp用法

1. Get操作（get操作参数是拼接在url后面的）

   public void doGet(View view) {
           //1.拿到okHttpClient对象
     //      OkHttpClient okHttpClient = new OkHttpClient();
           //2、构造Request
           Request.Builder builder = new Request.Builder();
           Request request = builder
                   .get()
                   .url(mBaseUrl+"login?username=cyd&password=1234")
                   .build();
           //3、4
           executeRequest(request);
       }

2. GAT、POST抽取出来的公共方法

   public void executeRequest(Request request ){
           //3、将Request封装为Call
           Call call = okHttpClient.newCall(request);
           //4、执行Call（回调的返回值是response,不在UI线程之内）
           call.enqueue(new Callback() {
               @Override
               public void onFailure(Request request, IOException e) {
                   L.e("onFailure"+e.getMessage());
               }
               @Override
               public void onResponse(Response response) throws IOException {
                   L.e("onResponse：");
                   final String str = response.body().string();
                   //             textView.setText(str);不能在子线程操作UI
                   //正确方法：
                   runOnUiThread(new Runnable() {
                       @Override
                       public void run() {
                           textView.setText(str);
                       }
                   });
               }
           });
   
       }

3. Post(post参数是构造一个请求体responseBody)

   public void doPost(View view) {
           //1.拿到okHttpClient对象
           //2、构造Request
           //2.1、构造requestBody
           //FormEncodingBuilder是传递post的参数的builder
           FormEncodingBuilder requestBodyBuilder = new FormEncodingBuilder();
           RequestBody requestBody = requestBodyBuilder
                   .add("username","cyd")
                   .add("password","123456789").build();
   
           Request.Builder builder = new Request.Builder();
           Request request = builder.url(mBaseUrl + "login").post(requestBody).build();
           //3、4
           executeRequest(request);
       }

4. POST一个JSON字符串

   public void doPostString(View view) {
           //将String作为requestBody发送出去，与上面不同的只有requestBody的构造方法
           //仅仅post字符串不需要使用FormEncodingBuilder的构造者模式
   
           //第一个参数包含类型和字符编码，第二个是字符串
           RequestBody requestBody = RequestBody.create(MediaType.parse("text/plain;chaset=utf-8"), "{username:cyd,password:09876}");
           Request.Builder builder = new Request.Builder();
           Request request = builder.url(mBaseUrl + "postString").post(requestBody).build();
           //3、4
           executeRequest(request);
       }

   服务端打印出字符串结果：

5. 服务端代码：

   public String login() {
           System.out.println(username+","+password);
           HttpServletResponse response = ServletActionContext.getResponse();
           try {
               PrintWriter writer = response.getWriter();
               writer.write("login success!");
               writer.flush();
           } catch (IOException e) {
               // TODO Auto-generated catch block
               e.printStackTrace();
           }        
           return null;        
       }
       public String postString() {
           HttpServletRequest request = ServletActionContext.getRequest();
           try {
               ServletInputStream iServletInputStream = request.getInputStream();
               
               StringBuilder sb = new StringBuilder();
               int len =0;
               byte[] buf = new byte[1024];
               while((len = iServletInputStream.read(buf))!= -1) {
                   sb.append(new String (buf,0 ,len));
               }
               System.out.println(sb.toString());
               
           } catch (IOException e) {
               // TODO Auto-generated catch block
               e.printStackTrace();
           }
           
           return null;
       }

6. 服务端接收参数是通过成员变量获取，客户端接收到服务端的数据一般是通过回调里面的response拿到inputStream，服务端获取客户端的数据流是通过request拿到的
7. session保持问题：用户登录后服务端会产生一个sessionID，sessionID会以cookie的形式返回给客户端，客户端拿到sessionID后若服务端sessionID还在生命周期中则可以不用重复登录，可以作为判断用户是否登录。可以获取sessionID
8. 笔记来源于：https://www.imooc.com/learn/764