@RequestMapping("/update")
    public Result login() {
        List<String> arr =new ArrayList<>();
        arr.add("123");
        arr.add("456");
        return  Result.success("获取成功",arr);
    }

public class Result {

    public Result(int code,String meg,Object data)
    {
    this.code=code;
    this.meg=meg;
    this.data=data;
    }

    private  int code;
    private  String meg;

    private Object data;

    public Object getData() {
        return data;
    }

    public void setData(Object data) {
        this.data = data;
    }

    public int getCode() {
        return code;
    }

    public void setCode(int code) {
        this.code = code;
    }

    public String getMeg() {
        return meg;
    }

    public void setMeg(String meg) {
        this.meg = meg;
    }


    public static Result success(String meg,Object data)
    {
    return  new Result(200,meg,data);
    }

    public static Result error(String meg,Object data)
    {
        return  new Result(-1,meg,data);
    }



    @Override
    public String toString() {
        return "Result{" +
                "code=" + code +
                ", meg='" + meg + '\'' +
                ", data=" + data +
                '}';
    }
}

如果返回的数据是 对象 或者 集合 就会自动转换成JSON格式

public class User {

    private String user;
    private String password;


    public String getUser() {
        return user;
    }

    public void setUser(String user) {
        this.user = user;
    }

    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password;
    }

    @Override
    public String toString() {
        return "User{" +
                "user='" + user + '\'' +
                ", password='" + password + '\'' +
                '}';
    }
}

 @RequestMapping("/update")
    public  User login(User user){
      return  user;
    }

如果是列表就会变成JSON数组形式

  @RequestMapping("/update")
    public  List<User> login(){
    
        List<User> list = new ArrayList<User>();
        
        User user = new User();
        for(int i=0;i<100;i++)
        {  user.setUser("123456");
           user.setPassword("dpc123");
           list.add(user);
        }
        
        return  list;
    }