This version is still in development and is not considered stable yet. For the latest stable version, please use Spring Framework 6.0.26!

ResponseEntity

See equivalent in the Reactive stack

ResponseEntity is like @ResponseBody but with status and headers. For example:

Java
Kotlin

@GetMapping("/something")
public ResponseEntity<String> handle() {
	String body = ... ;
	String etag = ... ;
	return ResponseEntity.ok().eTag(etag).body(body);
}

@GetMapping("/something")
fun handle(): ResponseEntity<String> {
	val body = ...
	val etag = ...
	return ResponseEntity.ok().eTag(etag).build(body)
}

Spring MVC supports using a single value reactive type to produce the ResponseEntity asynchronously, and/or single and multi-value reactive types for the body. This allows the following types of async responses:

ResponseEntity<Mono<T>> or ResponseEntity<Flux<T>> make the response status and headers known immediately while the body is provided asynchronously at a later point. Use Mono if the body consists of 0..1 values or Flux if it can produce multiple values.
Mono<ResponseEntity<T>> provides all three — response status, headers, and body, asynchronously at a later point. This allows the response status and headers to vary depending on the outcome of asynchronous request handling.