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| <h2 title="Annotation Type Asynchronous" class="title">Annotation Type Asynchronous</h2> |
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| <pre>@Documented |
| @Retention(value=RUNTIME) |
| @Target(value={METHOD,TYPE}) |
| @Inherited |
| public @interface <span class="memberNameLabel">Asynchronous</span></pre> |
| <div class="block">Wrap the execution and invoke it asynchronously. The context for <code>jakarta.enterprise.context.RequestScoped</code> |
| must be active during the method invocation, which means the method with the <code>@Asynchronous</code> annotation is |
| allowed to use the beans with <code>jakarta.enterprise.context.RequestScoped</code>. Any methods marked with this |
| annotation must return one of: |
| <ul> |
| <li><code>Future</code></li> |
| <li><code>CompletionStage</code></li> |
| </ul> |
| |
| Otherwise, <a href="../../../../org/eclipse/microprofile/faulttolerance/exceptions/FaultToleranceDefinitionException.html" title="class in org.eclipse.microprofile.faulttolerance.exceptions"><code>FaultToleranceDefinitionException</code></a> occurs during |
| deployment. The return type <code>CompletionStage</code> is preferred over |
| <code>Future</code> as a <code>Future</code> that completes exceptionally will not |
| trigger other Fault Tolerance operations even if specified (e.g. Retry), while a |
| <code>CompletionStage</code> that completes exceptionally will trigger other Fault Tolerance |
| capabilities if specified (e.g. Retry). |
| |
| <p> |
| When a method marked with this annotation is called from one thread (which we will call Thread A), the method call is |
| intercepted, and execution of the method is submitted to run asynchronously on another thread (which we will call |
| Thread B). |
| <p> |
| On Thread A, a Future or CompletionStage is returned immediately and can be used to get the result of the execution |
| taking place on Thread B, once it is complete. |
| <p> |
| Before the execution on Thread B completes, the Future or CompletionStage returned in Thread A will report itself as |
| incomplete. At this point, <code>Future.cancel(boolean)</code> can be used to abort the execution. |
| <p> |
| Once the execution on Thread B is complete, the Future or CompletionStage returned in Thread A behaves differently |
| depending on whether the execution in Thread B threw an exception: |
| <ul> |
| <li>If the execution threw an exception, the Future or CompletionStage will be completed with that exception.</li> |
| <li>If the execution returned normally, the Future or CompletionStage returned in Thread A will behave in the same |
| way as the Future or CompletionStage returned from the execution in Thread B, i.e. it can be: |
| <ul> |
| <li>not complete yet</li> |
| <li>completed successfully with a return value</li> |
| <li>completed exceptionally</li> |
| </ul> |
| <p> |
| At this point, any calls to the Future or CompletionStage returned in Thread A will be delegated to the Future or |
| CompletionStage returned from the execution in Thread B.</li> |
| </ul> |
| |
| <p> |
| The call made on Thread A will never throw an exception, even if the method declares that it throws checked |
| exceptions, because the execution is going to occur on Thread B and hasn't happened yet. To avoid unnecessary |
| <code>try..catch</code> blocks around these method calls, it's recommended that methods annotated with |
| <code>@Asynchronous</code> do not declare that they throw checked exceptions. |
| <p> |
| Any exception thrown from the execution on Thread B, or raised by another Fault Tolerance component such as |
| <a href="../../../../org/eclipse/microprofile/faulttolerance/Bulkhead.html" title="annotation in org.eclipse.microprofile.faulttolerance"><code>Bulkhead</code></a> or <a href="../../../../org/eclipse/microprofile/faulttolerance/CircuitBreaker.html" title="annotation in org.eclipse.microprofile.faulttolerance"><code>CircuitBreaker</code></a>, can be retrieved in the following ways: |
| <ul> |
| <li>If the method declares <code>Future</code> as the return type, calling |
| <code>Future.get()</code> on the Future returned in Thread A will throw an |
| <code>ExecutionException</code> wrapping the original exception.</li> |
| <li>If the method declares <code>CompletionStage</code> as the return type, the CompletionStage |
| returned in Thread A is completed exceptionally with the exception.</li> |
| </ul> |
| |
| <p> |
| If a class is annotated with this annotation, all class methods are treated as if they were marked with this |
| annotation. If one of the methods doesn't return either Future or CompletionStage, |
| <a href="../../../../org/eclipse/microprofile/faulttolerance/exceptions/FaultToleranceDefinitionException.html" title="class in org.eclipse.microprofile.faulttolerance.exceptions"><code>FaultToleranceDefinitionException</code></a> occurs (at deploy time |
| if the bean is discovered during deployment). |
| </p> |
| |
| <p> |
| Example usage: |
| </p> |
| |
| <pre> |
| <code>@Asynchronous |
| public CompletionStage<String> getString() { |
| return CompletableFuture.completedFuture("hello"); |
| }</code> |
| </pre> |
| |
| <p> |
| Example call with exception handling: |
| </p> |
| |
| <pre> |
| <code>CompletionStage stage = getString().exceptionally(e -> { |
| handleException(e); |
| return null; |
| });</code> |
| </pre></div> |
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