在Javaweb中使用JSON数据格式发送以及响应

在传统的Javaweb中数据发送以及响应的，我们通常使用servlet。随着技术的不断更新迭代，当我们使用axios发生json格式的数据时，我们后台之内使用json数据格式来进行响应。

1.如果我们在前端发送普通请求参数时，我们在后台还能使用servlet.getParameter方法接收

 前端使用VUE进行发送

new Vue({
    "el":"#app",
    "data":{},
    "methods":{
        "commonParam":function () {
            axios({
                "method":"post",
                "url":"/demo/AjaxServlet?method=commonParam",
                "params":{
                    "userName":"tom",
                    "userPwd":"123456"
                }
            }).then(function (response) {
                console.log(response);
            }).catch(function (error) {
                console.log(error);
            });
        }
    }
});

后端接收的相关代码 

请求的URL为：http://localhost:8080/demo/AjaxServlet?method=commonParam&userName=tom&userPwd=123456

public class AjaxServlet extends ModelBaseServlet {
    protected void commonParam(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

        String userName = request.getParameter("userName");
        String userPwd = request.getParameter("userPwd");

        System.out.println("userName = " + userName);
        System.out.println("userPwd = " + userPwd);

        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");

    }
}

2.现在我们发送请求JSON数据时

前台相关代码

……
"methods":{
    "requestBodyJSON":function () {
        axios({
            "method":"post",
            "url":"/demo/AjaxServlet?method=requestBodyJSON",
            "data":{
                "stuId": 55,
                "stuName": "tom",
                "subjectList": [
                    {
                        "subjectName": "java",
                        "subjectScore": 50.55
                    },
                    {
                        "subjectName": "php",
                        "subjectScore": 30.26
                    }
                ]
            }
        }).then(function (response) {
            console.log(response);
        }).catch(function (error) {
            console.log(error);
        });
    }
}
……

后端代码

1.加入Gson的jar包

Gson是Google研发的一款非常优秀的JSON数据解析和生成工具，它可以帮助我们将数据在JSON字符串和Java对象之间互相转换。

  //Gson有两个API
 //1.fromJson(string,T) 将字符串转化成java object
 //2.toJson(java Object) 将java object转化成json字符串，这样才能响应给客户端

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.服务器端返回JSON数据

前端

axios({
    "method":"post",
    "url":"/demo/AjaxServlet?method=responseBodyJSON"
}).then(function (response) {
    console.log(response);
}).catch(function (error) {
    console.log(error);
});

后端

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，MIME类型定义
    response.setContentType("application/json;charset=UTF-8");
    response.getWriter().write(json);

}