书城9 - 前后端 json 数据的交互

解析请求中的 json 数据，返回 json 数据

1. 加入 Gson.jar 包

2. 通过输入流读取数据，使用 Gson 对象解析字符串

• protected void requestBodyJSON(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
  
      // 1.由于请求体数据有可能很大，所以Servlet标准在设计API的时候要求我们通过输入流来读取
      BufferedReader reader = request.getReader();
  
      // 2.创建StringBuilder对象来累加存储从请求体中读取到的每一行
      StringBuilder builder = new StringBuilder();
  
      // 3.声明临时变量
      String bufferStr = null;
  
      // 4.循环读取
      while((bufferStr = reader.readLine()) != null) {
          builder.append(bufferStr);
      }
  
      // 5.关闭流
      reader.close();
  
      // 6.累加的结果就是整个请求体
      String requestBody = builder.toString();
  
      // 7.创建Gson对象用于解析JSON字符串
      Gson gson = new Gson();
  
      // 8.将JSON字符串还原为Java对象
      Student student = gson.fromJson(requestBody, Student.class);
      System.out.println("student = " + student);
  
      System.out.println("requestBody = " + requestBody);
  
      response.setContentType("text/html;charset=UTF-8");
      response.getWriter().write("服务器端返回普通文本字符串作为响应");
  }
  

3. 服务器封装 json 数据发送给客户端

• protected void responseBodyJSON(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
  
      // 1.准备数据对象
      Student student = new Student();
      student.setStuId(10);
      student.setStuName("tom");
      student.setSchool(new School(11,"atguigu"));
      student.setSubjectList(Arrays.asList(new Subject("java", 95.5), new Subject("php", 93.3)));
  
      Map<String, Teacher> teacherMap = new HashMap<>();
      teacherMap.put("t1", new Teacher("lili", 25));
      teacherMap.put("t2", new Teacher("mary", 26));
      teacherMap.put("t3", new Teacher("katty", 27));
  
      student.setTeacherMap(teacherMap);
  
      // 2.创建Gson对象
      Gson gson = new Gson();
  
      // 3.将Java对象转换为JSON对象
      String json = gson.toJson(student);
  
      // 4.设置响应体的内容类型
      response.setContentType("application/json;charset=UTF-8");
      response.getWriter().write(json);
  
  }