JSON入门到精通

册噩噩 2020-09-08 09:39:22

JSON的语法格式?
*对象表示为键值对
*数据由逗号分割
*花括号保存对象
*方括号保存数组

实例:
{"username":"十五万","age":"11","sex":"男"}
追加:
JSON是一种轻量级的数据交换格式，它基于JavaScript的一个子集.
JSON 是 JS 对象的字符串表示法，它使用文本表示一个 JS 对象的信息，本质是一个字符串。

JSON 和 JS 对象互转(这里我们用jackson这个,不用fastjson!)
var user = {
name :"孙伟浩",
age : 16,
sex : "男"
};

console.log(user);
js对象通过.stringfy(参数)来得到var形式的jason字符串
var str = JSON.stringify(user);
console.log(str);
用.parse(参数)方法把json字符串转成js对象形式
var obj = JSON.parse(str);
console.log(obj);



package com.example.fuxi.controller;



import com.example.fuxi.pojo.User;

import com.fasterxml.jackson.core.JsonProcessingException;

import com.fasterxml.jackson.databind.ObjectMapper;

import org.springframework.stereotype.Controller;

import org.springframework.web.bind.annotation.RequestMapping;

import org.springframework.web.bind.annotation.ResponseBody;



@Controller

public class UserController {



    //produce:指定响应体的返回类型和编码-----防止返回到页面乱码

    @RequestMapping(value = "/json",produces = "application/json;charset=utf-8")    //String 的转换格式 produces = "text/html;charset=utf-8"

    @ResponseBody

    public String json1(){

       

        User user = new User("十五万","11","男");

         

        ObjectMapper mapper = new ObjectMapper();  //需要一个jackson的对象映射器,也就是一个类,可以将对象转换为字符串



        String userJson = null;



        try {

            userJson = mapper.writeValueAsString(user);  //将一个java对象,转换成字符串

        } catch (JsonProcessingException e) {

            e.printStackTrace();

        }

        System.out.println(userJson);



        return userJson;

    }





}

对上面进行简化如下



   @RequestMapping(value = "/json2",produces = "application/json;charset=utf-8")    //String 的转换格式 produces = "text/html;charset=utf-8"

    @ResponseBody

    public String json2 () throws JsonProcessingException {

        User user = new User("李太白","26","男");

        return new ObjectMapper().writeValueAsString(user);

    }

list集合转换json



@RequestMapping(value = "/json3",produces = "application/json;charset=utf-8")    //String 的转换格式 produces = "text/html;charset=utf-8"

    @ResponseBody

    public String json3 () throws JsonProcessingException {

        List<User> list = new ArrayList<User>();

        list.add(new User("李太白1","26","男"));

        list.add(new User("李太白2","25","男"));

        list.add(new User("李太白3","24","男"))

        list.add(new User("李太白4","23","男"));

        return new ObjectMapper().writeValueAsString(list);

    }

通过配置文件设置json格式



<bean class="org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerMapping" />

    <bean class="org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter">

        <property name="messageConverters">

            <list>

                <bean class="org.springframework.http.converter.StringHttpMessageConverter">

                    <property name="supportedMediaTypes">

                        <list>

                            <value>text/html; charset=UTF-8</value>

                            <value>application/json;charset=UTF-8</value>

                        </list>

                    </property>

                </bean>

                <bean class="org.springframework.http.converter.json.MappingJackson2HttpMessageConverter">

                    <property name="supportedMediaTypes">

                        <list>

                            <value>text/html; charset=UTF-8</value>

                            <value>application/json;charset=UTF-8</value>

                        </list>

                    </property>

                </bean>

            </list>

        </property>

    </bean>