Return Values

See equivalent in the Reactive stack

The next table describes the supported controller method return values. Reactive types are supported for all return values.

Controller method return value Description

Controller method return value	Description
`@ResponseBody`	The return value is converted through `HttpMessageConverter` implementations and written to the response. See `@ResponseBody`.
`HttpEntity<B>`, `ResponseEntity<B>`	The return value that specifies the full response (including HTTP headers and body) is to be converted through `HttpMessageConverter` implementations and written to the response. See ResponseEntity.
`HttpHeaders`	For returning a response with headers and no body.
`ErrorResponse`, `ProblemDetail`	To render an RFC 9457 error response with details in the body, see Error Responses
`String`	A view name to be resolved with `ViewResolver` implementations and used together with the implicit model — determined through command objects and `@ModelAttribute` methods. The handler method can also programmatically enrich the model by declaring a `Model` argument (see Explicit Registrations).
`View`	A `View` instance to use for rendering together with the implicit model — determined through command objects and `@ModelAttribute` methods. The handler method can also programmatically enrich the model by declaring a `Model` argument (see Explicit Registrations).
`java.util.Map`, `org.springframework.ui.Model`	Attributes to be added to the implicit model, with the view name implicitly determined through a `RequestToViewNameTranslator`.
`@ModelAttribute`	An attribute to be added to the model, with the view name implicitly determined through a `RequestToViewNameTranslator`. Note that `@ModelAttribute` is optional. See "Any other return value" at the end of this table.
`ModelAndView` object	The view and model attributes to use and, optionally, a response status.
`FragmentsRendering`, `Collection<ModelAndView>`	For rendering one or more fragments each with its own view and model. See HTML Fragments for more details.
`void`	A method with a `void` return type (or `null` return value) is considered to have fully handled the response if it also has a `ServletResponse`, an `OutputStream` argument, or an `@ResponseStatus` annotation. The same is also true if the controller has made a positive `ETag` or `lastModified` timestamp check (see Controllers for details). If none of the above is true, a `void` return type can also indicate “no response body” for REST controllers or a default view name selection for HTML controllers.
`DeferredResult<V>`	Produce any of the preceding return values asynchronously from any thread — for example, as a result of some event or callback. See Asynchronous Requests and `DeferredResult`.
`Callable<V>`	Produce any of the above return values asynchronously in a Spring MVC-managed thread. See Asynchronous Requests and `Callable`.
`ListenableFuture<V>`, `java.util.concurrent.CompletionStage<V>`, `java.util.concurrent.CompletableFuture<V>`	Alternative to `DeferredResult`, as a convenience (for example, when an underlying service returns one of those).
`ResponseBodyEmitter`, `SseEmitter`	Emit a stream of objects asynchronously to be written to the response with `HttpMessageConverter` implementations. Also supported as the body of a `ResponseEntity`. See Asynchronous Requests and HTTP Streaming.
`StreamingResponseBody`	Write to the response `OutputStream` asynchronously. Also supported as the body of a `ResponseEntity`. See Asynchronous Requests and HTTP Streaming.
Reactor and other reactive types registered via `ReactiveAdapterRegistry`	A single value type, for example, `Mono`, is comparable to returning `DeferredResult`. A multi-value type, for example, `Flux`, may be treated as a stream depending on the requested media type, for example, "text/event-stream", "application/json+stream", or otherwise is collected to a List and rendered as a single value. See Asynchronous Requests and Reactive Types.
Other return values	If a return value remains unresolved in any other way, it is treated as a model attribute, unless it is a simple type as determined by BeanUtils#isSimpleProperty, in which case it remains unresolved.

@ResponseBody

The return value is converted through HttpMessageConverter implementations and written to the response. See @ResponseBody.

HttpEntity<B>, ResponseEntity<B>

The return value that specifies the full response (including HTTP headers and body) is to be converted through HttpMessageConverter implementations and written to the response. See ResponseEntity.

HttpHeaders

For returning a response with headers and no body.

ErrorResponse, ProblemDetail

To render an RFC 9457 error response with details in the body, see Error Responses

String

A view name to be resolved with ViewResolver implementations and used together with the implicit model — determined through command objects and @ModelAttribute methods. The handler method can also programmatically enrich the model by declaring a Model argument (see Explicit Registrations).

View

A View instance to use for rendering together with the implicit model — determined through command objects and @ModelAttribute methods. The handler method can also programmatically enrich the model by declaring a Model argument (see Explicit Registrations).

java.util.Map, org.springframework.ui.Model

Attributes to be added to the implicit model, with the view name implicitly determined through a RequestToViewNameTranslator.

@ModelAttribute

An attribute to be added to the model, with the view name implicitly determined through a RequestToViewNameTranslator.

Note that @ModelAttribute is optional. See "Any other return value" at the end of this table.

ModelAndView object

The view and model attributes to use and, optionally, a response status.

FragmentsRendering, Collection<ModelAndView>

For rendering one or more fragments each with its own view and model. See HTML Fragments for more details.

void

A method with a void return type (or null return value) is considered to have fully handled the response if it also has a ServletResponse, an OutputStream argument, or an @ResponseStatus annotation. The same is also true if the controller has made a positive ETag or lastModified timestamp check (see Controllers for details).

If none of the above is true, a void return type can also indicate “no response body” for REST controllers or a default view name selection for HTML controllers.

DeferredResult<V>

Produce any of the preceding return values asynchronously from any thread — for example, as a result of some event or callback. See Asynchronous Requests and DeferredResult.

Callable<V>

Produce any of the above return values asynchronously in a Spring MVC-managed thread. See Asynchronous Requests and Callable.

ListenableFuture<V>, java.util.concurrent.CompletionStage<V>, java.util.concurrent.CompletableFuture<V>

Alternative to DeferredResult, as a convenience (for example, when an underlying service returns one of those).

ResponseBodyEmitter, SseEmitter

Emit a stream of objects asynchronously to be written to the response with HttpMessageConverter implementations. Also supported as the body of a ResponseEntity. See Asynchronous Requests and HTTP Streaming.

StreamingResponseBody

Write to the response OutputStream asynchronously. Also supported as the body of a ResponseEntity. See Asynchronous Requests and HTTP Streaming.

Reactor and other reactive types registered via ReactiveAdapterRegistry

A single value type, for example, Mono, is comparable to returning DeferredResult. A multi-value type, for example, Flux, may be treated as a stream depending on the requested media type, for example, "text/event-stream", "application/json+stream", or otherwise is collected to a List and rendered as a single value. See Asynchronous Requests and Reactive Types.

Other return values

If a return value remains unresolved in any other way, it is treated as a model attribute, unless it is a simple type as determined by BeanUtils#isSimpleProperty, in which case it remains unresolved.