How to Return an HTTP 400 \'Bad Request\' Error in Spring MVC @ResponseBody Methods?

How to Handle HTTP Errors in Spring MVC @ResponseBody Methods

Problem:

When using Spring MVC with a @ResponseBody approach, how can a method respond with an HTTP 400 "bad request" error if a particular condition is not met?

Solution:

Original Approach:

The original code attempted to return a String if the condition was not met, which is not feasible since @ResponseBody expects a ResponseEntity object:

<code class="java">@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;
}</code>

Solution:

Change the method's return type to ResponseEntity, where T is the expected response type. This allows you to leverage the HttpStatus enumeration to specify the HTTP status code:

<code class="java">@ResponseBody
public ResponseEntity<String> match(@PathVariable String matchId) {
    String json = matchService.getMatchJson(matchId);
    if (json == null) {
        return new ResponseEntity<>(HttpStatus.BAD_REQUEST);
    }
    return new ResponseEntity<>(json, HttpStatus.OK);
}</code>

For a cleaner alternative after Spring 4.1, utilize the helper methods in ResponseEntity:

<code class="java">@ResponseBody
public ResponseEntity<String> match(@PathVariable String matchId) {
    String json = matchService.getMatchJson(matchId);
    if (json == null) {
        return ResponseEntity.status(HttpStatus.BAD_REQUEST).body(null);
    }
    return ResponseEntity.ok(json);
}</code>

This approach enables the return of an appropriate HTTP status code and content based on the execution result.

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