There was an unexpected error (type=Internal Server Error, status=500).

启用spring boot项目时，查看是否少了解析Ajax注解
修改前

浏览器报出如下错误

解决方案：
加入@ResponseBody 注解

@Controller
public class StudentController {

    @Resource
    private StudentService studentService;

    @RequestMapping("/query")
    @ResponseBody  //加入解析Ajax注解
    public String queryStudent(){
        Student student = studentService.queryStudent(123);
        return student.toString();
    }

}