jackson 如何将实体转json json字符串转实体

@Autowired
ObjectMapper objectMapper;

  String data = "";  //一个json串
  Student stu = new Student ();
　stu = objectMapper.readValue(data, Student .class);// json字符串转实体
public <T> String writeAsString(T t) throws JsonProcessingException {
    return objectMapper.writeValueAsString(t);
} 
String aa = writeAsString(stu);

    public <T> T readValue(String data) {
        try {
            return objectMapper.readValue(data, new TypeReference<T>() {
            });
        } catch (Exception e) {
            // TODO: handle exception
        }
        return null;
    }

        <dependency>
            <groupId>com.fasterxml.jackson.core</groupId>
            <artifactId>jackson-databind</artifactId>
            <version>2.11.1</version>
        </dependency>
 
        <dependency>
            <groupId>com.fasterxml.jackson.core</groupId>
            <artifactId>jackson-core</artifactId>
            <version>2.11.1</version>
        </dependency>
        <dependency>
            <groupId>com.fasterxml.jackson.core</groupId>
            <artifactId>jackson-annotations</artifactId>
            <version>2.11.1</version>
        </dependency>

/**
 * @Author : JCccc
 * @CreateTime : 2020/3/18
 * @Description :
 **/
public class UserEntity {
    private Integer id;
    private String name;
    private Integer age;
 
  // set get 方法 和 toString 等方法就不粘贴出来了
}

    public static void main(String[] args) throws JsonProcessingException {
        UserEntity userEntity=new UserEntity();
        userEntity.setId(100);
        userEntity.setName("JCccc");
        userEntity.setAge(18);
        ObjectMapper mapper = new ObjectMapper();
        String jsonString = mapper.writerWithDefaultPrettyPrinter()
                .writeValueAsString(userEntity);
        System.out.println(jsonString);
    }

        ObjectMapper mapper = new ObjectMapper();
        //json字符串转对象
        UserEntity userEntityNew = mapper.readValue(jsonString, UserEntity.class);
        System.out.println(userEntityNew);

        ObjectMapper mapper = new ObjectMapper();
        Map map=new HashMap();
        map.put("A",1);
        map.put("B",2);
        map.put("C",3);
        map.put("D",4);
        String jsonMap = mapper.writeValueAsString(map);
        System.out.println(jsonMap);

        ObjectMapper mapper = new ObjectMapper();
        //json字符串转为Map对象
        Map mapNew=mapper.readValue(jsonMap, Map.class);
        System.out.println(mapNew);

        ObjectMapper mapper = new ObjectMapper();
        UserEntity userEntity1=new UserEntity();
        userEntity1.setId(101);
        userEntity1.setName("JCccc1");
        userEntity1.setAge(18);
        UserEntity userEntity2=new UserEntity();
        userEntity2.setId(102);
        userEntity2.setName("JCccc2");
        userEntity2.setAge(18);
        UserEntity userEntity3=new UserEntity();
        userEntity3.setId(103);
        userEntity3.setName("JCccc3");
        userEntity3.setAge(18);
        List<UserEntity> userList=new ArrayList<>();
        userList.add(userEntity1);
        userList.add(userEntity2);
        userList.add(userEntity3);
        
        String jsonList = mapper.writeValueAsString(userList);
        System.out.println(jsonList);

        ObjectMapper mapper = new ObjectMapper();
        List<UserEntity> userListNew= mapper.readValue(jsonList,new TypeReference<List<UserEntity>>(){});
        System.out.println(userListNew.toString());

{
	"msg": "success",
	"data": [
		{
			"id": 101,
			"name": "JCccc1",
			"age": 18
		},
		{
			"id": 102,
			"name": "JCccc2",
			"age": 18
		},
		{
			"id": 103,
			"name": "JCccc3",
			"age": 18
		}
	],
	"status": 200
}

    @PostMapping("testJackson")
    public void testJackson(@RequestBody Map map) {
 
        System.out.println(map);
        String  msg = String.valueOf(map.get("msg"));
        System.out.println(msg);
        List dataList = (List) map.get("data");
        System.out.println(dataList.toString());
    }

    @PostMapping("testJackson")
    public void testJackson(@RequestBody String jsonStr) throws JsonProcessingException {
 
        System.out.println(jsonStr);
        ObjectMapper mapper = new ObjectMapper();
        Map map = mapper.readValue(jsonStr, Map.class);
        String  msg = String.valueOf(map.get("msg"));
        System.out.println(msg);
        String  status = String.valueOf(map.get("status"));
        System.out.println(status);
        List dataList = (List) map.get("data");
        System.out.println(dataList.toString());
    }