How to Fix a BeanCreationException for handlerExceptionResolver in Java Spring after Upgrading to Spring Boot 3.x and Spring 6.x?

Ah, the joys of upgrading to the latest and greatest versions of Spring Boot and Spring! While it’s exciting to take advantage of the new features and improvements, it’s not uncommon to encounter some pesky errors along the way. One such error that might have you scratching your head is the infamous BeanCreationException for handlerExceptionResolver. Fear not, dear reader, for we’re about to dive into the world of Spring configuration and troubleshooting to get you back on track!

The Problem: BeanCreationException for handlerExceptionResolver

After upgrading to Spring Boot 3.x and Spring 6.x, you might encounter an error message similar to this:

org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'handlerExceptionResolver' defined in class path resource [org/springframework/boot/autoconfigure/web/WebMvcAutoConfiguration.class]: Bean instantiation via factory method failed; 
nested exception is org.springframework.beans.BeanInstantiationException: Failed to instantiate [org.springframework.web.servlet.HandlerExceptionResolver]: Factory method 'handlerExceptionResolver' threw exception; 
nested exception is java.lang.ClassCastException: class org.springframework.web.servlet.mvc.method.annotation.ExceptionHandlerExceptionResolver cannot be cast to class org.springframework.web.servlet.HandlerExceptionResolver

This error is thrown when Spring attempts to create a bean for the handlerExceptionResolver, but fails due to a ClassCastException. But why does this happen, you ask? Well, let’s dig deeper into the changes introduced in Spring Boot 3.x and Spring 6.x.

Changes in Spring Boot 3.x and Spring 6.x

In Spring Boot 3.x and Spring 6.x, several changes were made to the WebMvcAutoConfiguration class, which affects the way exception resolvers are configured. Specifically:

• The HandlerExceptionResolver interface was replaced with the new exception resolver mechanism, which is based on the @ExceptionHandler annotation.
• The ExceptionHandlerExceptionResolver class was introduced as the default exception resolver for annotated controllers.
• The WebMvcConfigurer interface was updated to provide a more flexible way of customizing the exception resolver.

These changes might seem subtle, but they can cause issues if your application relies on custom exception resolvers or legacy configuration. Now, let’s get to the good stuff – fixing the error!

Fixing the BeanCreationException

To resolve the BeanCreationException, you’ll need to update your Spring configuration to comply with the new exception resolver mechanism. Here are the steps to follow:

Step 1: Update Your Maven or Gradle Dependencies

Make sure you’re using the correct versions of Spring Boot and Spring in your Maven or Gradle dependencies:

<dependency>
  <groupId>org.springframework.boot</groupId>
  <artifactId>spring-boot-starter-web</artifactId>
  <version>3.0.0</version>
</dependency>

<dependency>
  <groupId>org.springframework</groupId>
  <artifactId>spring-web</artifactId>
  <version>6.0.0</version>
</dependency>

Step 2: Create a Custom Exception Resolver

Create a custom exception resolver class that implements the HandlerExceptionResolver interface:

public class CustomExceptionResolver implements HandlerExceptionResolver {

  @Override
  public ModelAndView resolveException(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) {
    // Handle your custom exceptions here
    return new ModelAndView("error", "error", ex.getMessage());
  }
}

Step 3: Configure the Exception Resolver in WebMvcConfigurer

Update your WebMvcConfigurer implementation to register the custom exception resolver:

@Configuration
public class WebConfig implements WebMvcConfigurer {

  @Bean
  public HandlerExceptionResolver handlerExceptionResolver() {
    return new CustomExceptionResolver();
  }

  @Override
  public void configureHandlerExceptionResolvers(List<HandlerExceptionResolver> resolvers) {
    resolvers.add(handlerExceptionResolver());
  }
}

Step 4: Update Your Controllers with @ExceptionHandler

Update your controllers to use the @ExceptionHandler annotation:

@RestController
public class MyController {

  @ExceptionHandler(value = Exception.class)
  public ResponseEntity<>> handleException(Exception ex) {
    // Handle your custom exceptions here
    return ResponseEntity.status(HttpStatus.INTERNAL_SERVER_ERROR).body(ex.getMessage());
  }

  // Your controller methods...
}

Step 5: Verify Your Configuration

Restart your application, and verify that the custom exception resolver is working as expected. You can test this by throwing an exception from one of your controller methods and checking that the correct error response is returned.

Before	After
BeanCreationException for handlerExceptionResolver	Custom exception resolver works as expected

Conclusion

And there you have it, folks! With these steps, you should be able to fix the BeanCreationException for handlerExceptionResolver after upgrading to Spring Boot 3.x and Spring 6.x. Remember to update your Maven or Gradle dependencies, create a custom exception resolver, configure it in WebMvcConfigurer, update your controllers with @ExceptionHandler, and verify your configuration.

By following these steps, you’ll be well on your way to enjoying the benefits of the latest Spring Boot and Spring versions. Happy coding, and may your exceptions be handled with ease!

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