org.springframework.web.servlet.mvc.method.annotation

## Class ResponseBodyEmitter

- java.lang.Object
- - org.springframework.web.servlet.mvc.method.annotation.ResponseBodyEmitter

- Direct Known Subclasses:
    SseEmitter

      public class ResponseBodyEmitter
      extends Object

  A controller method return value type for asynchronous request processing where one or more objects are written to the response.

  While `DeferredResult` is used to produce a single result, a `ResponseBodyEmitter` can be used to send multiple objects where each object is written with a compatible `HttpMessageConverter`.

  Supported as a return type on its own as well as within a `ResponseEntity`.

       @RequestMapping(value="/stream", method=RequestMethod.GET)
       public ResponseBodyEmitter handle() {
                 ResponseBodyEmitter emitter = new ResponseBodyEmitter();
                 // Pass the emitter to another component...
                 return emitter;
       }

       // in another thread
       emitter.send(foo1);

       // and again
       emitter.send(foo2);

       // and done
       emitter.complete();

  Since:
    4.2
  Author:
    Rossen Stoyanchev, Juergen Hoeller

- - ### Nested Class Summary

    Nested Classes
    Modifier and Type | Class and Description
    --- | ---
    `static class` | `ResponseBodyEmitter.DataWithMediaType` A simple holder of data to be written along with a MediaType hint for selecting a message converter to write with.

  - ### Constructor Summary

    Constructors
    Constructor and Description
    `ResponseBodyEmitter()` Create a new ResponseBodyEmitter instance.
    `ResponseBodyEmitter(Long timeout)` Create a ResponseBodyEmitter with a custom timeout value.

  - ### Method Summary

    All Methods Instance Methods Concrete Methods
    Modifier and Type | Method and Description
    --- | ---
    `void` | `complete()` Complete request processing by performing a dispatch into the servlet container, where Spring MVC is invoked once more, and completes the request processing lifecycle.
    `void` | `completeWithError(Throwable ex)` Complete request processing with an error.
    `protected void` | `extendResponse(ServerHttpResponse outputMessage)` Invoked after the response is updated with the status code and headers, if the ResponseBodyEmitter is wrapped in a ResponseEntity, but before the response is committed, i.e.
    `Long` | `getTimeout()` Return the configured timeout value, if any.
    `void` | `onCompletion(Runnable callback)` Register code to invoke when the async request completes.
    `void` | `onError(Consumer<Throwable> callback)` Register code to invoke for an error during async request processing.
    `void` | `onTimeout(Runnable callback)` Register code to invoke when the async request times out.
    `void` | `send(Object object)` Write the given object to the response.
    `void` | `send(Object object, MediaType mediaType)` Overloaded variant of `send(Object)` that also accepts a MediaType hint for how to serialize the given Object.
    `String` | `toString()`

    - ### Methods inherited from class java.lang.Object

      `clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait`

- - ### Constructor Detail

    - #### ResponseBodyEmitter

          public ResponseBodyEmitter()

      Create a new ResponseBodyEmitter instance.

    - #### ResponseBodyEmitter

          public ResponseBodyEmitter(Long timeout)

      Create a ResponseBodyEmitter with a custom timeout value.

      By default not set in which case the default configured in the MVC Java Config or the MVC namespace is used, or if that's not set, then the timeout depends on the default of the underlying server.

      Parameters:
        `timeout` - the timeout value in milliseconds

  - ### Method Detail

    - #### getTimeout

          @Nullable
          public Long getTimeout()

      Return the configured timeout value, if any.

    - #### extendResponse

          protected void extendResponse(ServerHttpResponse outputMessage)

      Invoked after the response is updated with the status code and headers, if the ResponseBodyEmitter is wrapped in a ResponseEntity, but before the response is committed, i.e. before the response body has been written to.

      The default implementation is empty.

    - #### send

          public void send(Object object)
                    throws IOException

      Write the given object to the response.

      If any exception occurs a dispatch is made back to the app server where Spring MVC will pass the exception through its exception handling mechanism.

      Note: if the send fails with an IOException, you do not need to call `completeWithError(Throwable)` in order to clean up. Instead the Servlet container creates a notification that results in a dispatch where Spring MVC invokes exception resolvers and completes processing.

      Parameters:
        `object` - the object to write
      Throws:
        `IOException` - raised when an I/O error occurs
        `IllegalStateException` - wraps any other errors

    - #### send

          public void send(Object object,
                           @Nullable
                           MediaType mediaType)
                    throws IOException

      Overloaded variant of `send(Object)` that also accepts a MediaType hint for how to serialize the given Object.
      Parameters:
        `object` - the object to write
        `mediaType` - a MediaType hint for selecting an HttpMessageConverter
      Throws:
        `IOException` - raised when an I/O error occurs
        `IllegalStateException` - wraps any other errors

    - #### complete

          public void complete()

      Complete request processing by performing a dispatch into the servlet container, where Spring MVC is invoked once more, and completes the request processing lifecycle.

      Note: this method should be called by the application to complete request processing. It should not be used after container related events such as an error while `sending`.

    - #### completeWithError

          public void completeWithError(Throwable ex)

      Complete request processing with an error.

      A dispatch is made into the app server where Spring MVC will pass the exception through its exception handling mechanism. Note however that at this stage of request processing, the response is committed and the response status can no longer be changed.

      Note: this method should be called by the application to complete request processing with an error. It should not be used after container related events such as an error while `sending`.

    - #### onTimeout

          public void onTimeout(Runnable callback)

      Register code to invoke when the async request times out. This method is called from a container thread when an async request times out.

    - #### onError

          public void onError(Consumer<Throwable> callback)

      Register code to invoke for an error during async request processing. This method is called from a container thread when an error occurred while processing an async request.
      Since:
        5.0

    - #### onCompletion

          public void onCompletion(Runnable callback)

      Register code to invoke when the async request completes. This method is called from a container thread when an async request completed for any reason including timeout and network error. This method is useful for detecting that a `ResponseBodyEmitter` instance is no longer usable.

    - #### toString

          public String toString()

      Overrides:
        `toString` in class `Object`