The controller of springboot returns an object. How can the front end receive json data?

    @RequestMapping(value="getUserById")
    @ResponseBody
    public User getUserById(int userId){
        System.out.println("userId="+userId);
        return businessService.getUserById(userId);
    }

result of browser call:

Tue Oct 30 13:46:21 CST 2018
There was an unexpected error (type=Internal Server Error, status=500).
No converter found for return value of type: class com.sunlei.springboot.model.User

won"t springboot do the default json conversion? I think all kinds of jackson packages have been imported into maven. What settings are missing?

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MySQL Query : SELECT * FROM `codeshelper`.`v9_news` WHERE status=99 AND catid='6' ORDER BY rand() LIMIT 5
MySQL Error : Disk full (/tmp/#sql-temptable-64f5-1b3ab8c-2b59c.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
MySQL Errno : 1021
Message : Disk full (/tmp/#sql-temptable-64f5-1b3ab8c-2b59c.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
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