Spring @ControllerAdvice

Spring Framework provides a feature called @ControllerAdvice that allows developers to provide a centralized advice for all controllers within an application. The advice can be in the form of exception handling, or providing default values for model attributes, or even adding additional response headers. In this article, we will explore what @ControllerAdvice is, how to use it, and some best practices for working with it in Spring.

What is @ControllerAdvice?

@ControllerAdvice is a Spring annotation that is used to provide advice for all controllers within an application. The advice can be in the form of exception handling, model attribute population, or response header customization. When a @ControllerAdvice class is annotated, it becomes a global point of control for all controllers within an application.

How to use @ControllerAdvice

To use @ControllerAdvice, you need to create a class that is annotated with @ControllerAdvice. The class should have methods annotated with @ExceptionHandler, @ModelAttribute, or @InitBinder to provide the advice.

• Exception Handling
  The @ExceptionHandler annotation is used to handle exceptions thrown by controllers. You can use the @ExceptionHandler annotation to define a method that will be called when an exception is thrown. For example, you can create a method to handle a NullPointerException:

@ControllerAdvice
public class ErrorControllerAdvice {
	
	@ExceptionHandler(NullPointerException.class)
	public ResponseEntity<String> handleNullPointer(NullPointerException ex) {		
		return new ResponseEntity<String>("Error", HttpStatus.INTERNAL_SERVER_ERROR);
	}
}

• Model Attribute Population
  The @ModelAttribute annotation is used to add attributes to the model for all controllers. For example, you can create a method that adds a default value for a model attribute:

@ControllerAdvice
public class ModelAttributeAdvice {

	@ModelAttribute
	public void addAttributes(Model model) {
		model.addAttribute("attributeName", "attributeValue");
	}
}

• Response Header Customization
  The @InitBinder annotation is used to customize the response headers. For example, you can create a method that adds a custom header to all responses:

@ControllerAdvice public class ResponseHeaderAdvice {

	@InitBinder
	public void initBinder(HttpServletResponse response) {
		response.setHeader("headerName", "headerValue");
	}
}

Best practices for working with @ControllerAdvice

Use separate classes for different types of advice: It is recommended to keep different types of advice separate, for example, use separate classes for exception handling and model attribute population.

Keep advice simple: The advice provided by @ControllerAdvice should be simple and straightforward. Avoid adding complex logic in the advice methods.

Reuse advice: You can reuse the advice provided by @ControllerAdvice across multiple controllers. This makes it easy to manage and maintain the advice.

In conclusion, @ControllerAdvice is a useful feature in Spring Framework that allows developers to provide centralized advice for all controllers within an application. Whether you need to handle exceptions, populate model attributes, or customize response headers, @ControllerAdvice provides a simple and flexible way to achieve this. By following these best practices, you can effectively use @ControllerAdvice