Exception Handling in Spring MVC

Exception handling in Spring MVC involves managing and processing exceptions that occur during the execution of a web request. This guide covers the key concepts and techniques for implementing exception handling in Spring MVC, including using the @ExceptionHandler annotation, the @ControllerAdvice annotation, and custom exception handlers.

Key Concepts of Exception Handling

• @ExceptionHandler: Handles exceptions thrown by request handling methods in the same controller.
• @ControllerAdvice: A specialization of the @Component annotation for handling exceptions across the whole application.
• ResponseEntityExceptionHandler: A convenient base class for controller advice classes that wish to provide centralized exception handling across all request mappings.

Using @ExceptionHandler

The @ExceptionHandler annotation is used to define a method that handles exceptions thrown by request handling methods in the same controller:

Example:

// UserController.java
package com.example.springmvc.controllers;

import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.ExceptionHandler;
import org.springframework.ui.Model;
import org.springframework.web.bind.annotation.ResponseBody;

@Controller
public class UserController {
    @GetMapping("/causeError")
    public String causeError() {
        throw new RuntimeException("An error occurred");
    }

    @ExceptionHandler(RuntimeException.class)
    @ResponseBody
    public String handleException(RuntimeException e) {
        return "Handled exception: " + e.getMessage();
    }
}

Using @ControllerAdvice

The @ControllerAdvice annotation is used to define a class that handles exceptions across the whole application:

Example:

// GlobalExceptionHandler.java
package com.example.springmvc.handlers;

import org.springframework.web.bind.annotation.ControllerAdvice;
import org.springframework.web.bind.annotation.ExceptionHandler;
import org.springframework.ui.Model;
import org.springframework.web.bind.annotation.ResponseBody;

@ControllerAdvice
public class GlobalExceptionHandler {
    @ExceptionHandler(Exception.class)
    @ResponseBody
    public String handleException(Exception e) {
        return "Global exception handler: " + e.getMessage();
    }
}

Custom Exception Handling

You can create custom exception handlers by extending ResponseEntityExceptionHandler:

CustomExceptionHandler.java

// CustomExceptionHandler.java
package com.example.springmvc.handlers;

import org.springframework.http.HttpHeaders;
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.context.request.WebRequest;
import org.springframework.web.servlet.mvc.method.annotation.ResponseEntityExceptionHandler;

@ControllerAdvice
public class CustomExceptionHandler extends ResponseEntityExceptionHandler {
    @ExceptionHandler(RuntimeException.class)
    protected ResponseEntity