SpringMVC writes objects back to json format

When not using the spring framework, we convert the object into json by importing the jar package, and then write the following code

// 使用json的转换工具将对象转换成json格式字符串再返回
// 原生形式
ObjectMapper objectMapper = new ObjectMapper();
String json = objectMapper.writeValueAsString(user);

After using SpringMVC, this operation can be handed over to spring to do

1. Import the mvc namespace in the spring-mvc.xml configuration file

<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:context="http://www.springframework.org/schema/context"
       xmlns:mvc="http://www.springframework.org/schema/mvc"
       xsi:schemaLocation="
                            http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd
                            http://www.springframework.org/schema/mvc http://www.springframework.org/schema/mvc/spring-mvc.xsd
                            http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsd
">

That is to add these two sentences

2. Configure annotation driver

<mvc:annotation-driven/>

3. Test results
   I use a User object to test, there are only two attributes in the User class: username and age

// 回写json格式
    @RequestMapping("/testReturnJson")
    @ResponseBody
    // 期望spring框架将对象直接转换成json对象
    public User test(){
    
    
        User user = new User();
        user.setUsername("zhangsan");
        user.setAge(18);
        return user;
    }

operation result