SpringBoot Exception 처리하기 SpringBoot Exception Handling

• When developing with SpringBoot, there are situations where Exception handling becomes necessary. I want to document how to handle exceptions in such cases and what methods are available.

Handling Exceptions

• Let’s work by adding Exceptions to the controller one by one

Creating Basic Controller and Return Object

• Let’s create a basic controller and an object to hold in the controller’s Response

• The controller and object were created as follows

  // Controller class
  package com.example.springcontrolleradvice.controller;
  
  import org.springframework.http.ResponseEntity;
  import org.springframework.web.bind.annotation.*;
  
  @RestController
  @RequestMapping("/orders")
  public class OrderController {
  
      @GetMapping("/{orderId}")
      public ResponseEntity<CommonResponse> getOrder(@PathVariable String orderId) {
          return ResponseEntity.ok(new CommonResponse("success", "order found", orderId));
      }
  }
  
  

  • When sending a GET request to /orders/{orderId}, it returns the orderId in the Response

  // Controller's Response object
  package com.example.springcontrolleradvice.controller;
  
  public record CommonResponse(
  String Status,
  String message,
  Object data
  ) {}
  

Adding Exception

• Let’s throw an Exception in the controller when orderId is not 100

  package com.example.springcontrolleradvice.controller;
  
  
  import org.springframework.http.ResponseEntity;
  import org.springframework.web.bind.annotation.*;
  
  @RestController
  @RequestMapping("/orders")
  public class OrderController {
  
      @GetMapping("/{orderId}")
      public ResponseEntity<CommonResponse> getOrder(@PathVariable String orderId) throws Exception {
          if(!orderId.equals("100")){
              throw new Exception("order not found");
          }
          return ResponseEntity.ok(new CommonResponse("success", "order found", orderId));
      }
  
  }
  
  

  • When Exception is applied as above, the Exception appears in the log when orderID is not 100

Creating Custom Exception

• Let’s create a CustomException by inheriting from the occurring Exception

  package com.example.springcontrolleradvice.controller.exception;
  
  public class CustomException extends RuntimeException {
      private String message;
      private String errorCode;
      private String hint;
  
      protected CustomException() {
      }
  
      public CustomException(String message, String errorCode, String hint) {
          this.message = message;
          this.errorCode = errorCode;
          this.hint = hint;
      }
  
      // getters and setters
  }
  
  

Applying CustomException to Controller

package com.example.springcontrolleradvice.controller;

import com.example.springcontrolleradvice.controller.exception.CustomException;
import org.springframework.http.ResponseEntity;
import org.springframework.web.bind.annotation.*;

@RestController
RequestMapping("/orders")

public class OrderController {

    @GetMapping("/{orderId}")
    public ResponseEntity<CommonResponse> getOrder(@PathVariable String orderId) {
        if (!orderId.equals("100")) {
            throw new CustomException("order not found", "ERROR400", "please check the order id");
        }
        return ResponseEntity.ok(new CommonResponse("success", "order found", orderId));
    }

}

• When CustomException is applied, CustomException is thrown when an Exception occurs

Creating Handler for CustomException

• The process above only throws an Exception when an Exception occurs. The CustomException message we want is not returned.
• Let’s include our CustomException in the returned message when throwing an Exception
• Let’s create a place to intercept Exceptions and return our CustomException

• Let’s write CustomExceptionInterceptor

  package com.example.springcontrolleradvice.controller.exception;
  
  
  import org.springframework.http.HttpStatus;
  import org.springframework.http.ResponseEntity;
  import org.springframework.web.bind.annotation.ControllerAdvice;
  import org.springframework.web.bind.annotation.ExceptionHandler;
  import org.springframework.web.servlet.mvc.method.annotation.ResponseEntityExceptionHandler;
  
  @ControllerAdvice
  public class CustomExceptionInterceptor extends ResponseEntityExceptionHandler {
  
      @ExceptionHandler(CustomException.class)
      public final ResponseEntity<Object> handleCustomException(CustomException ex) {
          CustomExceptionModel exceptionResponse = new CustomExceptionModel(ex.getMessage(), ex.getErrorCode(), ex.getHint());
          return new ResponseEntity(exceptionResponse, HttpStatus.INTERNAL_SERVER_ERROR);
      }
  }
  

  • Using @ControllerAdvice, we create a place to intercept Exceptions
  • Inherit from ResponseEntityExceptionHandler to make CustomExceptionInterceptor intercept when Exceptions occur

  • CustomExceptionModel is written as a message object with the same structure as CustomException

    package com.example.springcontrolleradvice.controller.exception;
    
    public record CustomExceptionModel(
            String message,
            String errorCode,
            String hint
    ) {
    }
    

    • Returns the exception with the message we wrote