org.springframework.web.context.request.async

## Interface DeferredResultProcessingInterceptor

All Known Implementing Classes:
  DeferredResultProcessingInterceptorAdapter, TimeoutDeferredResultProcessingInterceptor

    public interface DeferredResultProcessingInterceptor

Intercepts concurrent request handling, where the concurrent result is obtained by waiting for a `DeferredResult` to be set from a thread chosen by the application (e.g. in response to some external event).

A `DeferredResultProcessingInterceptor` is invoked before the start of async processing, after the `DeferredResult` is set as well as on timeout, or or after completing for any reason including a timeout or network error.

As a general rule exceptions raised by interceptor methods will cause async processing to resume by dispatching back to the container and using the Exception instance as the concurrent result. Such exceptions will then be processed through the `HandlerExceptionResolver` mechanism.

The `afterTimeout` method can set the `DeferredResult` in order to resume processing.

Since:
  3.2
Author:
  Rossen Stoyanchev, Rob Winch

### Method Summary

Methods
`<T> void` `afterCompletion(NativeWebRequest request, DeferredResult<T> deferredResult)` Invoked from a container thread when an async request completed for any reason including timeout and network error.
`<T> void` `beforeConcurrentHandling(NativeWebRequest request, DeferredResult<T> deferredResult)` Invoked immediately before the start of concurrent handling, in the same thread that started it.
`<T> boolean` `handleTimeout(NativeWebRequest request, DeferredResult<T> deferredResult)` Invoked from a container thread when an async request times out before the `DeferredResult` has been set.
`<T> void` `postProcess(NativeWebRequest request, DeferredResult<T> deferredResult, Object concurrentResult)` Invoked after a `DeferredResult` has been set, via `DeferredResult.setResult(Object)` or `DeferredResult.setErrorResult(Object)`, and is also ready to handle the concurrent result.
`<T> void` `preProcess(NativeWebRequest request, DeferredResult<T> deferredResult)` Invoked immediately after the start of concurrent handling, in the same thread that started it.

### Method Detail

#### beforeConcurrentHandling

    <T> void beforeConcurrentHandling(NativeWebRequest request,
                                    DeferredResult<T> deferredResult)
                                  throws Exception

Invoked immediately before the start of concurrent handling, in the same thread that started it. This method may be used to capture state just prior to the start of concurrent processing with the given `DeferredResult`.

Parameters:
  `request` - the current request
  `deferredResult` - the DeferredResult for the current request
Throws:
  `Exception` - in case of errors

#### preProcess

    <T> void preProcess(NativeWebRequest request,
                      DeferredResult<T> deferredResult)
                    throws Exception

Invoked immediately after the start of concurrent handling, in the same thread that started it. This method may be used to detect the start of concurrent processing with the given `DeferredResult`.

The `DeferredResult` may have already been set, for example at the time of its creation or by another thread.

Parameters:
  `request` - the current request
  `deferredResult` - the DeferredResult for the current request
Throws:
  `Exception` - in case of errors

#### postProcess

    <T> void postProcess(NativeWebRequest request,
                       DeferredResult<T> deferredResult,
                       Object concurrentResult)
                     throws Exception

Invoked after a `DeferredResult` has been set, via `DeferredResult.setResult(Object)` or `DeferredResult.setErrorResult(Object)`, and is also ready to handle the concurrent result.

This method may also be invoked after a timeout when the `DeferredResult` was created with a constructor accepting a default timeout result.

Parameters:
  `request` - the current request
  `deferredResult` - the DeferredResult for the current request
  `concurrentResult` - the result to which the `DeferredResult`
Throws:
  `Exception` - in case of errors

#### handleTimeout

    <T> boolean handleTimeout(NativeWebRequest request,
                            DeferredResult<T> deferredResult)
                          throws Exception

Invoked from a container thread when an async request times out before the `DeferredResult` has been set. Implementations may invoke `setResult` or `setErrorResult` to resume processing.

Parameters:
  `request` - the current request
  `deferredResult` - the DeferredResult for the current request; if the `DeferredResult` is set, then concurrent processing is resumed and subsequent interceptors are not invoked
Returns:
  `true` if processing should continue, or `false` if other interceptors should not be invoked
Throws:
  `Exception` - in case of errors

#### afterCompletion

    <T> void afterCompletion(NativeWebRequest request,
                           DeferredResult<T> deferredResult)
                         throws Exception

Invoked 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 `DeferredResult` instance is no longer usable.

Parameters:
  `request` - the current request
  `deferredResult` - the DeferredResult for the current request
Throws:
  `Exception` - in case of errors