Exception처리
1. 에러페이지
2. 4,500번대 에러
3. client가 200 외에 처리를 하지 못할때 200을 내려주고 별도의 에러 메시지 전달
보통 두가지 방법이 있다.
@ControllerAdvice: Global 예외처리및 특정 Package/Controller예외 처리
@ExceptionHandler: 특정 Controller의 예외 처리

예제코드

package com.example.exception.dto;

import javax.validation.constraints.Min;
import javax.validation.constraints.NotEmpty;
import javax.validation.constraints.NotNull;
import javax.validation.constraints.Size;

public class User {
    @NotEmpty
    @Size(min=1, max = 10)
    private String name;

    @Min(1)
    @NotNull
    private Integer age;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

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

package com.example.exception.controller;

import com.example.exception.dto.User;
import org.springframework.http.HttpStatus;
import org.springframework.http.ResponseEntity;
import org.springframework.web.bind.MethodArgumentNotValidException;
import org.springframework.web.bind.annotation.*;

import javax.validation.Valid;

@RestController
@RequestMapping("/api/user")
public class ApiController {

    @GetMapping("")
    public User get(@RequestParam (required = false) String name, @RequestParam (required = false) Integer age){
        //required false: RequestParam이 없어도 동작하되 null값이 됨
        User user=new User();
        user.setName(name);
        user.setAge(age);
        int a=10+age;

        return user;
    }

    @PostMapping("")
    public User post(@Valid @RequestBody User user){
        System.out.println(user);
        return user;
    }

    @ExceptionHandler(value = MethodArgumentNotValidException.class)
    public ResponseEntity MethodArgumentNotValidException(MethodArgumentNotValidException e){
        System.out.println("api controller");
        return ResponseEntity.status(HttpStatus.BAD_REQUEST).body(e.getMessage());
    }

}

package com.example.exception.advice;

import org.springframework.http.HttpStatus;
import org.springframework.http.ResponseEntity;
import org.springframework.web.bind.MethodArgumentNotValidException;
import org.springframework.web.bind.annotation.ExceptionHandler;
import org.springframework.web.bind.annotation.RestController;
import org.springframework.web.bind.annotation.RestControllerAdvice;

@RestControllerAdvice
public class GlobalControllerAdvice {

    @ExceptionHandler(value = Exception.class)
    public ResponseEntity exception(Exception e){
        System.out.println(e.getClass().getName());

        System.out.println("----------");
        System.out.println(e.getLocalizedMessage());
        System.out.println("----------");
        return ResponseEntity.status(HttpStatus.INTERNAL_SERVER_ERROR).body("");
    }

    @ExceptionHandler(value = MethodArgumentNotValidException.class)
    public ResponseEntity MethodArgumentNotValidException(MethodArgumentNotValidException e){
        return ResponseEntity.status(HttpStatus.BAD_REQUEST).body(e.getMessage());
    }

}