Exception handling in Spring Boot

The ability to correctly handle errors in APIs while providing meaningful error messages is a very desirable feature that helps the API client to respond to issues appropriately. In this shot, we will go over how to do proper exception handling with Spring Boot, an open-source Java-framework for building micro-services.

Spring Annotations

Let’s look at two Spring annotations that we will be use to handle exceptions:

• @ExceptionHandler
• @ControllerAdvice

ExceptionHandler

The @ExceptionHandler is an annotation used to handle exceptions thrown during the execution of handlers and send custom responses to the client.

The most common way to use @ExceptionHandler is on methods of @ControllerAdvice classes so that the exception handling is applied globally.

ControllerAdvice

The @ControllerAdvice annotation handles exceptions globally – it allows you to use the same ExceptionHandler for multiple controllers. This way, we can define how to treat an exception in just one place because this handler will be called whenever the exception is thrown from classes that are covered by ControllerAdvice.

Code

Let’s use @ExceptionHandler and @ControllerAdvice to define a central point for treating exceptions and wrapping them up in a class.

Handling exceptions

We first define a class that will handle the exceptions. Let’s call it ExampleExceptionHandler.

Next, we will define a custom exception class called ExampleException:

public class ExampleException extends RuntimeException {
 
    public ExampleException(String message) {
        super(message);
    }
}

It’s a good practice to name your exceptions specifically. We are only using the names ExampleException and ExampleExceptionHandler for illustration.

Finally, we can handle our new exception:

@ControllerAdvice
public class ExampleExceptionHandler extends ResponseEntityExceptionHandler {
  
   @ExceptionHandler(ExampleException.class)
   protected ResponseEntity<Object> exception(ExampleException exception) {
       String errorMsg = "Example error message";
       return new ResponseEntity<>(errorMsg, HttpStatus.BAD_REQUEST);
   }
   // more exception handlers...
}

Overriding exception handlers

You can also override the existing exception handlers. Spring Boot’s built-in exception class ResponseEntityExceptionHandler has multiple methods that you can override to customize the exception handling further.

We extend the ExampleExceptionHandler class with the ResponseEntityExceptionHandler class, and override the handleHttpMessageNotReadable() method:

@ControllerAdvice
public class ExampleExceptionHandler extends ResponseEntityExceptionHandler {

   @Override
   protected ResponseEntity<Object> handleHttpMessageNotReadable(HttpMessageNotReadableException ex, HttpHeaders headers, HttpStatus status, WebRequest request) {
       String errorMsg = "Example error message";
       return new ResponseEntity<>(errorMsg, HttpStatus.BAD_REQUEST);
   }
   // more exception handlers ...
}