org.springframework.web.context.request.async

## Class WebAsyncManager

- java.lang.Object
- - org.springframework.web.context.request.async.WebAsyncManager

-     public final class WebAsyncManager
      extends Object

  The central class for managing asynchronous request processing, mainly intended as an SPI and not typically used directly by application classes.

  An async scenario starts with request processing as usual in a thread (T1). Concurrent request handling can be innitiated by calling startCallableProcessing or startDeferredResultProcessing both of which produce a result in a separate thread (T2). The result is saved and the request dispatched to the container, to resume processing with the saved result in a third thread (T3). Within the dispatched thread (T3), the saved result can be accessed via `getConcurrentResult()` or its presence detected via `hasConcurrentResult()`.

  Since:
    3.2
  Author:
    Rossen Stoyanchev
  See Also:
    `AsyncWebRequestInterceptor`, `AsyncHandlerInterceptor`, `OncePerRequestFilter.shouldNotFilterAsyncDispatch()`, `OncePerRequestFilter.isAsyncDispatch(javax.servlet.http.HttpServletRequest)`

- - ### Method Summary

    Methods
    Modifier and Type | Method and Description
    --- | ---
    `void` | `clearConcurrentResult()` Clear concurrentResult and concurrentResultContext.
    `CallableProcessingInterceptor` | `getCallableInterceptor(Object key)` Get the `CallableProcessingInterceptor` registered under the given key.
    `Object` | `getConcurrentResult()` Provides access to the result from concurrent handling.
    `Object[]` | `getConcurrentResultContext()` Provides access to additional processing context saved at the start of concurrent handling.
    `DeferredResultProcessingInterceptor` | `getDeferredResultInterceptor(Object key)` Get the `DeferredResultProcessingInterceptor` registered under the given key.
    `boolean` | `hasConcurrentResult()` Whether a result value exists as a result of concurrent handling.
    `boolean` | `isConcurrentHandlingStarted()` Whether the selected handler for the current request chose to handle the request asynchronously.
    `void` | `registerCallableInterceptor(Object key, CallableProcessingInterceptor interceptor)` Register a `CallableProcessingInterceptor` under the given key.
    `void` | `registerCallableInterceptors(CallableProcessingInterceptor... interceptors)` Register a `CallableProcessingInterceptor` without a key.
    `void` | `registerDeferredResultInterceptor(Object key, DeferredResultProcessingInterceptor interceptor)` Register a `DeferredResultProcessingInterceptor` under the given key.
    `void` | `registerDeferredResultInterceptors(DeferredResultProcessingInterceptor... interceptors)` Register a `DeferredResultProcessingInterceptor` without a key.
    `void` | `setAsyncWebRequest(AsyncWebRequest asyncWebRequest)` Configure the `AsyncWebRequest` to use.
    `void` | `setTaskExecutor(AsyncTaskExecutor taskExecutor)` Configure an AsyncTaskExecutor for use with concurrent processing via `startCallableProcessing(Callable, Object...)`.
    `void` | `startCallableProcessing(Callable<?> callable, Object... processingContext)` Start concurrent request processing and execute the given task with an `AsyncTaskExecutor`.
    `void` | `startCallableProcessing(WebAsyncTask<?> webAsyncTask, Object... processingContext)` Use the given `WebAsyncTask` to configure the task executor as well as the timeout value of the `AsyncWebRequest` before delegating to `startCallableProcessing(Callable, Object...)`.
    `void` | `startDeferredResultProcessing(DeferredResult<?> deferredResult, Object... processingContext)` Start concurrent request processing and initialize the given `DeferredResult` with a `DeferredResult.DeferredResultHandler` that saves the result and dispatches the request to resume processing of that result.

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

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

- - ### Method Detail

    - #### setAsyncWebRequest

          public void setAsyncWebRequest(AsyncWebRequest asyncWebRequest)

      Configure the `AsyncWebRequest` to use. This property may be set more than once during a single request to accurately reflect the current state of the request (e.g. following a forward, request/response wrapping, etc). However, it should not be set while concurrent handling is in progress, i.e. while `isConcurrentHandlingStarted()` is `true`.
      Parameters:
        `asyncWebRequest` - the web request to use

    - #### setTaskExecutor

          public void setTaskExecutor(AsyncTaskExecutor taskExecutor)

      Configure an AsyncTaskExecutor for use with concurrent processing via `startCallableProcessing(Callable, Object...)`.

      By default a `SimpleAsyncTaskExecutor` instance is used.

    - #### isConcurrentHandlingStarted

          public boolean isConcurrentHandlingStarted()

      Whether the selected handler for the current request chose to handle the request asynchronously. A return value of "true" indicates concurrent handling is under way and the response will remain open. A return value of "false" means concurrent handling was either not started or possibly that it has completed and the request was dispatched for further processing of the concurrent result.

    - #### hasConcurrentResult

          public boolean hasConcurrentResult()

      Whether a result value exists as a result of concurrent handling.

    - #### getConcurrentResult

          public Object getConcurrentResult()

      Provides access to the result from concurrent handling.
      Returns:
        an Object, possibly an `Exception` or `Throwable` if concurrent handling raised one.
      See Also:
        `clearConcurrentResult()`

    - #### getConcurrentResultContext

          public Object[] getConcurrentResultContext()

      Provides access to additional processing context saved at the start of concurrent handling.
      See Also:
        `clearConcurrentResult()`

    - #### getCallableInterceptor

          public CallableProcessingInterceptor getCallableInterceptor(Object key)

      Get the `CallableProcessingInterceptor` registered under the given key.
      Parameters:
        `key` - the key
      Returns:
        the interceptor registered under that key or `null`

    - #### getDeferredResultInterceptor

          public DeferredResultProcessingInterceptor getDeferredResultInterceptor(Object key)

      Get the `DeferredResultProcessingInterceptor` registered under the given key.
      Parameters:
        `key` - the key
      Returns:
        the interceptor registered under that key or `null`

    - #### registerCallableInterceptor

          public void registerCallableInterceptor(Object key,
                                         CallableProcessingInterceptor interceptor)

      Register a `CallableProcessingInterceptor` under the given key.
      Parameters:
        `key` - the key
        `interceptor` - the interceptor to register

    - #### registerCallableInterceptors

          public void registerCallableInterceptors(CallableProcessingInterceptor... interceptors)

      Register a `CallableProcessingInterceptor` without a key. The key is derived from the class name and hashcode.
      Parameters:
        `interceptors` - one or more interceptors to register

    - #### registerDeferredResultInterceptor

          public void registerDeferredResultInterceptor(Object key,
                                               DeferredResultProcessingInterceptor interceptor)

      Register a `DeferredResultProcessingInterceptor` under the given key.
      Parameters:
        `key` - the key
        `interceptor` - the interceptor to register

    - #### registerDeferredResultInterceptors

          public void registerDeferredResultInterceptors(DeferredResultProcessingInterceptor... interceptors)

      Register a `DeferredResultProcessingInterceptor` without a key. The key is derived from the class name and hashcode.
      Parameters:
        `interceptors` - one or more interceptors to register

    - #### clearConcurrentResult

          public void clearConcurrentResult()

      Clear concurrentResult and concurrentResultContext.

    - #### startCallableProcessing

          public void startCallableProcessing(Callable<?> callable,
                                     Object... processingContext)
                                       throws Exception

      Start concurrent request processing and execute the given task with an `AsyncTaskExecutor`. The result from the task execution is saved and the request dispatched in order to resume processing of that result. If the task raises an Exception then the saved result will be the raised Exception.
      Parameters:
        `callable` - a unit of work to be executed asynchronously
        `processingContext` - additional context to save that can be accessed via `getConcurrentResultContext()`
      Throws:
        `Exception` - If concurrent processing failed to start
      See Also:
        `getConcurrentResult()`, `getConcurrentResultContext()`

    - #### startCallableProcessing

          public void startCallableProcessing(WebAsyncTask<?> webAsyncTask,
                                     Object... processingContext)
                                       throws Exception

      Use the given `WebAsyncTask` to configure the task executor as well as the timeout value of the `AsyncWebRequest` before delegating to `startCallableProcessing(Callable, Object...)`.
      Parameters:
        `webAsyncTask` - an WebAsyncTask containing the target `Callable`
        `processingContext` - additional context to save that can be accessed via `getConcurrentResultContext()`
      Throws:
        `Exception` - If concurrent processing failed to start

    - #### startDeferredResultProcessing

          public void startDeferredResultProcessing(DeferredResult<?> deferredResult,
                                           Object... processingContext)
                                             throws Exception

      Start concurrent request processing and initialize the given `DeferredResult` with a `DeferredResult.DeferredResultHandler` that saves the result and dispatches the request to resume processing of that result. The `AsyncWebRequest` is also updated with a completion handler that expires the `DeferredResult` and a timeout handler assuming the `DeferredResult` has a default timeout result.
      Parameters:
        `deferredResult` - the DeferredResult instance to initialize
        `processingContext` - additional context to save that can be accessed via `getConcurrentResultContext()`
      Throws:
        `Exception` - If concurrent processing failed to start
      See Also:
        `getConcurrentResult()`, `getConcurrentResultContext()`