Basics about ResponseEntity to maniputale HTTP Response

ResponseEntity represents the whole HTTP response: status code, headers, and body. Because of it, we can use it to fully configure the HTTP response.

If we want to use it, we have to return it from the endpoint; Spring takes care of the rest.

ResponseEntity is a generic type. As a result, we can use any type as the response body:

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@GetMapping("/hello") ResponseEntity<String> hello() {     return new ResponseEntity<>("Hello World!", HttpStatus.OK); }

Since we specify the response status programmatically, we can return with different status codes for different scenarios:

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@GetMapping("/age") ResponseEntity<String> age(   @RequestParam("yearOfBirth") int yearOfBirth) {        if (isInFuture(yearOfBirth)) {         return new ResponseEntity<>(           "Year of birth cannot be in the future",           HttpStatus.BAD_REQUEST);     }     return new ResponseEntity<>(       "Your age is " + calculateAge(yearOfBirth),       HttpStatus.OK); }

Additionally, we can set HTTP headers:

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@GetMapping("/customHeader") ResponseEntity<String> customHeader() {     HttpHeaders headers = new HttpHeaders();     headers.add("Custom-Header", "foo");               return new ResponseEntity<>(       "Custom header set", headers, HttpStatus.OK); }

Furthermore, ResponseEntity provides two nested builder interfaces: HeadersBuilder and its subinterface, BodyBuilder. Hence we can access their capabilities through the static methods of ResponseEntity.

The simplest case is a response with a body and HTTP 200 response code:

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@GetMapping("/hello") ResponseEntity<String> hello() {     return ResponseEntity.ok("Hello World!"); }

For the most popular HTTP status codes we get static methods:

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BodyBuilder accepted(); BodyBuilder badRequest(); BodyBuilder created(java.net.URI location); HeadersBuilder<?> noContent(); HeadersBuilder<?> notFound(); BodyBuilder ok();

In addition, we can use the BodyBuilder status(HttpStatus status) and the BodyBuilder status(int status) methods to set any HTTP status.

Finally with ResponseEntity<T> BodyBuilder.body(T body) we can set the HTTP response body:

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@GetMapping("/age") ResponseEntity<String> age(@RequestParam("yearOfBirth") int yearOfBirth) {     if (isInFuture(yearOfBirth)) {         return ResponseEntity.badRequest()             .body("Year of birth cannot be in the future");     }     return ResponseEntity.status(HttpStatus.OK)         .body("Your age is " + calculateAge(yearOfBirth)); }

We can also set custom headers:

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@GetMapping("/customHeader") ResponseEntity<String> customHeader() {     return ResponseEntity.ok()         .header("Custom-Header", "foo")         .body("Custom header set"); }

Hence BodyBuilder.body() returns a ResponseEntity instead of BodyBuilder, it should be the last call.

Note, that with HeaderBuilder we can’t set any properties of the response body.

While returning ResponseEntity<T> object from the controller, we might get some exception or error while processing the request and would like to return error-related information to the user represented as some other type let’s say E.

Spring 3.2 brings support for a global @ExceptionHandler with the new @ControllerAdvice annotation handles these kinds of scenarios. For in-depth details

While ResponseEntity is very powerful, we shouldn’t overuse it. In simple cases, there’re other options that satisfy our needs and they result in much cleaner code.