java - Spring Boot customize http error response?

Question

How can I customize the response status code and the data in the response body if an exception occurs in a Spring Boot web application?

I have created a web app that throws a custom exception if something unexpected occurs due to some bad internal state. Consequently, the response body of the request that triggered the error looks something like:

HTTP/1.1 500 Internal Server Error
{
    "timestamp": 1412685688268,
    "status": 500,
    "error": "Internal Server Error",
    "exception": "com.example.CustomException",
    "message": null,
    "path": "/example"
}

---

Now, I would like to change the status code and set the fields in the response body. One solution that crossed my mind was something like:

@ControllerAdvice
class CustomResponseEntityExceptionHandler extends ResponseEntityExceptionHandler {

    @ExceptionHandler
    @ResponseStatus(HttpStatus.BAD_REQUEST)
    @ResponseBody
    ErrorMessage handleBadCredentials(CustomException e) {
        return new ErrorMessage("Bad things happened");
    }
}

@XmlRootElement
public class ErrorMessage(
    private String error;

    public ErrorMessage() {
    }

    public ErrorMessage(String error) {
        this.error = error;
    }

    public String getError() {
        return error;
    }

    public void setError(String error) {
        this.error = error;
    }
)

However, that created (as suspected) a completely different response:

HTTP/1.1 400 Bad Request
{
    "error": "Bad things happened"
}

Answer 1

As @zeroflagL mentioned, Spring Boot fabricates the "standard" error response body in org.springframework.boot.autoconfigure.web.DefaultErrorAttributes. Similar to your needs, I wanted to leverage all of that, but simply augment one more "type" field that was provided by some of my exceptions.

I did that by implementing a Component that sub-classed DefaultErrorAttributes. Spring Boot automatically picked it up and used mine instead of the default.

@Component
public class ExtendedErrorAttributes extends DefaultErrorAttributes {
    @Override
    public Map<String, Object> getErrorAttributes(RequestAttributes requestAttributes, 
                                                  boolean includeStackTrace) {
        final Map<String, Object> errorAttributes = 
            super.getErrorAttributes(requestAttributes, 
                                     includeStackTrace);

        final Throwable error = super.getError(requestAttributes);
        if (error instanceof TypeProvider) {
            final TypeProvider typeProvider = (TypeProvider) error;
            errorAttributes.put("type", typeProvider.getTypeIdentifier());
        }

        return errorAttributes;
    }
}

With that, I get an augmented JSON response body, such as

{
  "timestamp": 1488058582764,
  "status": 429,
  "error": "Too Many Requests",
  "exception": "com.example.ExternalRateLimitException",
  "message": "DAILY_LIMIT: too many requests",
  "path": "/api/lookup",
  "type": "DAILY_LIMIT"
}