How to respond with HTTP 400 error in a Spring MVC @ResponseBody method returning String?

By | November 29, 2017
Questions:

I’m using Spring MVC for a simple JSON API, with @ResponseBody based approach like the following. (I already have a service layer producing JSON directly.)

@RequestMapping(value = "/matches/{matchId}", produces = "application/json")
@ResponseBody
public String match(@PathVariable String matchId) {
    String json = matchService.getMatchJson(matchId);
    if (json == null) {
        // TODO: how to respond with e.g. 400 "bad request"?
    }
    return json;
}

Question is, in the given scenario, what is the simplest, cleanest way to respond with a HTTP 400 error?

I did come across approaches like:

return new ResponseEntity(HttpStatus.BAD_REQUEST);

…but I can’t use it here since my method’s return type is String, not ResponseEntity.

Answers:

change your return type to ResponseEntity<>, then you can use below for 400

return new ResponseEntity<>(HttpStatus.BAD_REQUEST);

and for correct request

return new ResponseEntity<>(json,HttpStatus.OK);

UPDATE 1

after spring 4.1 there are helper methods in ResponseEntity could be used as

return ResponseEntity.status(HttpStatus.BAD_REQUEST).body(null);

and

return ResponseEntity.ok(json);

Questions:
Answers:

Something like this should work, I’m not sure whether or not there is a simpler way:

@RequestMapping(value = "/matches/{matchId}", produces = "application/json")
@ResponseBody
public String match(@PathVariable String matchId, @RequestBody String body,
            HttpServletRequest request, HttpServletResponse response) {
    String json = matchService.getMatchJson(matchId);
    if (json == null) {
        response.setStatus( HttpServletResponse.SC_BAD_REQUEST  );
    }
    return json;
}

Questions:
Answers:

Not necessarily the most compact way of doing this, but quite clean IMO

if(json == null) {
    throw new BadThingException();
}
...

@ExceptionHandler(BadThingException.class)
@ResponseStatus(value = HttpStatus.BAD_REQUEST)
public @ResponseBody MyError handleException(BadThingException e) {
    return new MyError("That doesnt work");
}

Edit you can use @ResponseBody in the exception handler method if using Spring 3.1+, otherwise use a ModelAndView or something.

https://jira.springsource.org/browse/SPR-6902

Questions:
Answers:

I would change the implementation slightly:

First, I create a UnknownMatchException:

@ResponseStatus(HttpStatus.NOT_FOUND)
public class UnknownMatchException extends RuntimeException {
    public UnknownMatchException(String matchId) {
        super("Unknown match: " + matchId);
    }
}

Note the use of @ResponseStatus, which will be recognized by Spring’s ResponseStatusExceptionResolver. If the exception is thrown, it will create a response with the corresponding response status. (I also took the liberty of changing the status code to 404 - Not Found which I find more appropriate for this use case, but you can stick to HttpStatus.BAD_REQUEST if you like.)


Next, I would change the MatchService to have the following signature:

interface MatchService {
    public Match findMatch(String matchId);
}

Finally, I would update the controller and delegate to Spring’s MappingJackson2HttpMessageConverter to handle the JSON serialization automatically (it is added by default if you add Jackson to the classpath and add either @EnableWebMvc or <mvc:annotation-driven /> to your config, see the reference docs):

@RequestMapping(value = "/matches/{matchId}", produces = MediaType.APPLICATION_JSON_VALUE)
@ResponseBody
public Match match(@PathVariable String matchId) {
    // throws an UnknownMatchException if the matchId is not known 
    return matchService.findMatch(matchId);
}

Note, it is very common to separate the domain objects from the view objects or DTO objects. This can easily be achieved by adding a small DTO factory that returns the serializable JSON object:

@RequestMapping(value = "/matches/{matchId}", produces = MediaType.APPLICATION_JSON_VALUE)
@ResponseBody
public MatchDTO match(@PathVariable String matchId) {
    Match match = matchService.findMatch(matchId);
    return MatchDtoFactory.createDTO(match);
}

Questions:
Answers:

Here’s a different approach. Create a custom Exception annotated with @ResponseStatus, like the following one.

@ResponseStatus(code = HttpStatus.NOT_FOUND, reason = "Not Found")
public class NotFoundException extends Exception {

    public NotFoundException() {
    }
}

And throw it when needed.

@RequestMapping(value = "/matches/{matchId}", produces = "application/json")
@ResponseBody
public String match(@PathVariable String matchId) {
    String json = matchService.getMatchJson(matchId);
    if (json == null) {
        throw new NotFoundException();
    }
    return json;
}

Check out the Spring documentation here: http://docs.spring.io/spring/docs/current/spring-framework-reference/htmlsingle/#mvc-ann-annotated-exceptions.

Questions:
Answers:

As mentioned in some answers, there is the ability to create an exception class for each HTTP status that you want to return. I don’t like the idea of having to create a class per status for each project. Here is what I came up with instead.

  • Create a generic exception that accepts an HTTP status
  • Create an Controller Advice exception handler

Let’s get to the code

package com.javaninja.cam.exception;

import org.springframework.http.HttpStatus;


/**
 * The exception used to return a status and a message to the calling system.
 * @author norrisshelton
 */
@SuppressWarnings("ClassWithoutNoArgConstructor")
public class ResourceException extends RuntimeException {

    private HttpStatus httpStatus = HttpStatus.INTERNAL_SERVER_ERROR;

    /**
     * Gets the HTTP status code to be returned to the calling system.
     * @return http status code.  Defaults to HttpStatus.INTERNAL_SERVER_ERROR (500).
     * @see HttpStatus
     */
    public HttpStatus getHttpStatus() {
        return httpStatus;
    }

    /**
     * Constructs a new runtime exception with the specified HttpStatus code and detail message.
     * The cause is not initialized, and may subsequently be initialized by a call to {@link #initCause}.
     * @param httpStatus the http status.  The detail message is saved for later retrieval by the {@link
     *                   #getHttpStatus()} method.
     * @param message    the detail message. The detail message is saved for later retrieval by the {@link
     *                   #getMessage()} method.
     * @see HttpStatus
     */
    public ResourceException(HttpStatus httpStatus, String message) {
        super(message);
        this.httpStatus = httpStatus;
    }
}

Then I create a controller advice class

package com.javaninja.cam.spring;


import com.javaninja.cam.exception.ResourceException;

import org.springframework.http.ResponseEntity;
import org.springframework.web.bind.annotation.ExceptionHandler;


/**
 * Exception handler advice class for all SpringMVC controllers.
 * @author norrisshelton
 * @see org.springframework.web.bind.annotation.ControllerAdvice
 */
@org.springframework.web.bind.annotation.ControllerAdvice
public class ControllerAdvice {

    /**
     * Handles ResourceExceptions for the SpringMVC controllers.
     * @param e SpringMVC controller exception.
     * @return http response entity
     * @see ExceptionHandler
     */
    @ExceptionHandler(ResourceException.class)
    public ResponseEntity handleException(ResourceException e) {
        return ResponseEntity.status(e.getHttpStatus()).body(e.getMessage());
    }
}

To use it

throw new ResourceException(HttpStatus.BAD_REQUEST, "My message");

http://javaninja.net/2016/06/throwing-exceptions-messages-spring-mvc-controller/

Questions:
Answers:

I m using this in my spring boot application

@RequestMapping(value = "/matches/{matchId}", produces = "application/json")
@ResponseBody
public ResponseEntity<?> match(@PathVariable String matchId, @RequestBody String body,
            HttpServletRequest request, HttpServletResponse response) {

    Product p;
    try {
      p = service.getProduct(request.getProductId());
    } catch(Exception ex) {
       return new ResponseEntity<String>(HttpStatus.BAD_REQUEST);
    }

    return new ResponseEntity(p, HttpStatus.OK);
}

Questions:
Answers:

With Spring Boot, I’m not entirely sure why this was necessary (I got the /error fallback even though @ResponseBody was defined on an @ExceptionHandler), but the following in itself did not work:

@ResponseBody
@ResponseStatus(HttpStatus.BAD_REQUEST)
@ExceptionHandler(IllegalArgumentException.class)
public ErrorMessage handleIllegalArguments(HttpServletRequest httpServletRequest, IllegalArgumentException e) {
    log.error("Illegal arguments received.", e);
    ErrorMessage errorMessage = new ErrorMessage();
    errorMessage.code = 400;
    errorMessage.message = e.getMessage();
    return errorMessage;
}

It still threw an exception, apparently because no producible media types were defined as a request attribute:

// AbstractMessageConverterMethodProcessor
@SuppressWarnings("unchecked")
protected <T> void writeWithMessageConverters(T value, MethodParameter returnType,
        ServletServerHttpRequest inputMessage, ServletServerHttpResponse outputMessage)
        throws IOException, HttpMediaTypeNotAcceptableException, HttpMessageNotWritableException {

    Class<?> valueType = getReturnValueType(value, returnType);
    Type declaredType = getGenericType(returnType);
    HttpServletRequest request = inputMessage.getServletRequest();
    List<MediaType> requestedMediaTypes = getAcceptableMediaTypes(request);
    List<MediaType> producibleMediaTypes = getProducibleMediaTypes(request, valueType, declaredType);
if (value != null && producibleMediaTypes.isEmpty()) {
        throw new IllegalArgumentException("No converter found for return value of type: " + valueType);   // <-- throws
    }

// ....

@SuppressWarnings("unchecked")
protected List<MediaType> getProducibleMediaTypes(HttpServletRequest request, Class<?> valueClass, Type declaredType) {
    Set<MediaType> mediaTypes = (Set<MediaType>) request.getAttribute(HandlerMapping.PRODUCIBLE_MEDIA_TYPES_ATTRIBUTE);
    if (!CollectionUtils.isEmpty(mediaTypes)) {
        return new ArrayList<MediaType>(mediaTypes);

So I added them.

@ResponseBody
@ResponseStatus(HttpStatus.BAD_REQUEST)
@ExceptionHandler(IllegalArgumentException.class)
public ErrorMessage handleIllegalArguments(HttpServletRequest httpServletRequest, IllegalArgumentException e) {
    Set<MediaType> mediaTypes = new HashSet<>();
    mediaTypes.add(MediaType.APPLICATION_JSON_UTF8);
    httpServletRequest.setAttribute(HandlerMapping.PRODUCIBLE_MEDIA_TYPES_ATTRIBUTE, mediaTypes);
    log.error("Illegal arguments received.", e);
    ErrorMessage errorMessage = new ErrorMessage();
    errorMessage.code = 400;
    errorMessage.message = e.getMessage();
    return errorMessage;
}

And this got me through to have a “supported compatible media type”, but then it still didn’t work, because my ErrorMessage was faulty:

public class ErrorMessage {
    int code;

    String message;
}

JacksonMapper did not handle it as “convertable”, so I had to add getters/setters, and I also added @JsonProperty annotation

public class ErrorMessage {
    @JsonProperty("code")
    private int code;

    @JsonProperty("message")
    private String message;

    public int getCode() {
        return code;
    }

    public void setCode(int code) {
        this.code = code;
    }

    public String getMessage() {
        return message;
    }

    public void setMessage(String message) {
        this.message = message;
    }
}

Then I received my message as intended

{"code":400,"message":"An \"url\" parameter must be defined."}

Questions:
Answers:

I think this thread actually has the easiest, cleanest solution, that does not sacrifice the JSON martialing tools that Spring provides:

https://stackoverflow.com/a/16986372/1278921

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