org.springframework.web.context.request.async

Class DeferredResult<T>

java.lang.Object

org.springframework.web.context.request.async.DeferredResult<T>

public class DeferredResult<T>
extends Object

DeferredResult provides an alternative to using a Callable for asynchronous request processing. While a Callable is executed concurrently on behalf of the application, with a DeferredResult the application can produce the result from a thread of its choice.

Subclasses can extend this class to easily associate additional data or behavior with the DeferredResult. For example, one might want to associate the user used to create the DeferredResult by extending the class and adding an additional property for the user. In this way, the user could easily be accessed later without the need to use a data structure to do the mapping.

An example of associating additional behavior to this class might be realized by extending the class to implement an additional interface. For example, one might want to implement Comparable so that when the DeferredResult is added to a PriorityQueue it is handled in the correct order.

Since:

3.2

Author:

Rossen Stoyanchev, Rob Winch

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static interface	DeferredResult.DeferredResultHandler Handles a DeferredResult value when set.

Constructor Summary

Constructors

Constructor and Description
DeferredResult() Create a DeferredResult.
DeferredResult(long timeout) Create a DeferredResult with a timeout value.
DeferredResult(Long timeout, Object timeoutResult) Create a DeferredResult with a timeout value and a default result to use in case of timeout.

Method Summary

Modifier and Type	Method and Description
Object	getResult()
boolean	hasResult()
boolean	isSetOrExpired() Return true if this DeferredResult is no longer usable either because it was previously set or because the underlying request expired.
void	onCompletion(Runnable callback) Register code to invoke when the async request completes.
void	onTimeout(Runnable callback) Register code to invoke when the async request times out.
boolean	setErrorResult(Object result) Set an error value for the DeferredResult and handle it.
boolean	setResult(T result) Set the value for the DeferredResult and handle it.
void	setResultHandler(DeferredResult.DeferredResultHandler resultHandler) Provide a handler to use to handle the result value.

Methods inherited from class java.lang.Object

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

Constructor Detail

DeferredResult

public DeferredResult()

Create a DeferredResult.

DeferredResult

public DeferredResult(long timeout)

Create a DeferredResult with a timeout value.

Parameters:

timeout - timeout value in milliseconds

DeferredResult

public DeferredResult(Long timeout,
                      Object timeoutResult)

Create a DeferredResult with a timeout value and a default result to use in case of timeout.

Parameters:

timeout - timeout value in milliseconds; ignored if null

timeoutResult - the result to use

Method Detail

isSetOrExpired

public final boolean isSetOrExpired()

Return true if this DeferredResult is no longer usable either because it was previously set or because the underlying request expired.

The result may have been set with a call to setResult(Object), or setErrorResult(Object), or as a result of a timeout, if a timeout result was provided to the constructor. The request may also expire due to a timeout or network error.

hasResult

public boolean hasResult()

Returns:

true if the DeferredResult has been set.

getResult

public Object getResult()

Returns:

the result or null if the result wasn't set; since the result can also be null, it is recommended to use hasResult() first to check if there is a result prior to calling this method.

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 before the DeferredResult has been set. It may invoke setResult or setErrorResult to resume processing.

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 DeferredResult instance is no longer usable.

setResultHandler

public final void setResultHandler(DeferredResult.DeferredResultHandler resultHandler)

Provide a handler to use to handle the result value.

Parameters:

resultHandler - the handler

See Also:

DeferredResultProcessingInterceptor

setResult

public boolean setResult(T result)

Set the value for the DeferredResult and handle it.

Parameters:

result - the value to set

Returns:

"true" if the result was set and passed on for handling; "false" if the result was already set or the async request expired.

See Also:

isSetOrExpired()

setErrorResult

public boolean setErrorResult(Object result)

Set an error value for the DeferredResult and handle it. The value may be an Exception or Throwable in which case it will be processed as if a handler raised the exception.

Parameters:

result - the error result value

Returns:

"true" if the result was set to the error value and passed on for handling; "false" if the result was already set or the async request expired.

See Also:

isSetOrExpired()