how do we handle duplicate key exception

[ashishsoni]

hi , would it be possible to show an example how we can handle exception raised for example DuplicateKeyException

[callicoder]

Hi Ashish,

You can handle exceptions with Spring-Webflux in the same way you handle exceptions in Spring MVC.

You can use an @ExceptionHandler in the controller to handle exceptions thrown in that controller or you can use a @ControllerAdvice to handle exceptions globally. -

The example below shows how to use @ExceptionHandler -

// Custom Exception
package com.example.webfluxdemo.exception;

public class TweetNotFoundException extends RuntimeException {
    public TweetNotFoundException(String tweetId) {
        super("Tweet not found with id " + tweetId);
    }
}

// The Controller Method which throws an exception if tweet was not found with the given id

@GetMapping("/tweets/{id}")
public Mono<Tweet> getTweetById(@PathVariable(value = "id") String tweetId) {
    return tweetRepository.findById(tweetId)
            .switchIfEmpty(Mono.error(new TweetNotFoundException(tweetId)));
}

// Exception Handler Method

@ExceptionHandler
public ResponseEntity handleNotFoundException(TweetNotFoundException ex) {
    return ResponseEntity.notFound().build();
}

Similarly, If the createTweet() endpoint throws DataIntegrityViolationException, then you can use an exception handler like this -

@ExceptionHandler
public ResponseEntity handleDuplicateKeyException(DuplicateKeyException ex) {
    return ResponseEntity.status(HttpStatus.CONFLICT).build();
}

I've added these examples in the repository as well.