The @asynchronous annotation was introduced in EJB 3.1 as a simple way of creating asynchronous processing.
Asynchronous Processing is when a caller returns immediately without waiting for the invoked method to complete.
Here, in JobProcessorTest,
final Future<String> red = processor.addJob("red");
proceeds to the next statement,
final Future<String> orange = processor.addJob("orange");
without waiting for the addJob() method to complete. And later we could ask for the result using the Future<?>.get() method like
assertEquals("blue", blue.get());
It waits for the processing to complete (if its not completed already) and gets the result. If you did not care about the result, you could simply have your asynchronous method as a void method.
Future Object from docs,
A Future represents the result of an asynchronous computation. Methods are provided to check if the computation is complete, to wait for its completion, and to retrieve the result of the computation. The result can only be retrieved using method get when the computation has completed, blocking if necessary until it is ready. Cancellation is performed by the cancel method. Additional methods are provided to determine if the task completed normally or was cancelled. Once a computation has completed, the computation cannot be cancelled. If you would like to use a Future for the sake of cancellability but not provide a usable result, you can declare types of the form Future<?> and return null as a result of the underlying task
@Singleton
public class JobProcessor {
@Asynchronous
@Lock(READ)
@AccessTimeout(-1)
public Future addJob(String jobName) {
// Pretend this job takes a while
doSomeHeavyLifting();
// Return our result
return new AsyncResult(jobName);
}
private void doSomeHeavyLifting() {
try {
Thread.sleep(SECONDS.toMillis(10));
} catch (InterruptedException e) {
Thread.interrupted();
throw new IllegalStateException(e);
}
}
}
public class JobProcessorTest extends TestCase {
public void test() throws Exception {
final Context context = EJBContainer.createEJBContainer().getContext();
final JobProcessor processor = (JobProcessor) context.lookup("java:global/async-methods/JobProcessor");
final long start = System.nanoTime();
// Queue up a bunch of work
final Future red = processor.addJob("red");
final Future orange = processor.addJob("orange");
final Future yellow = processor.addJob("yellow");
final Future green = processor.addJob("green");
final Future blue = processor.addJob("blue");
final Future violet = processor.addJob("violet");
// Wait for the result -- 1 minute worth of work
assertEquals("blue", blue.get());
assertEquals("orange", orange.get());
assertEquals("green", green.get());
assertEquals("red", red.get());
assertEquals("yellow", yellow.get());
assertEquals("violet", violet.get());
// How long did it take?
final long total = TimeUnit.NANOSECONDS.toSeconds(System.nanoTime() - start);
// Execution should be around 9 - 21 seconds
assertTrue("" + total, total > 9);
assertTrue("" + total, total < 21);
}
}
#Running
-------------------------------------------------------
T E S T S
-------------------------------------------------------
Running org.superbiz.async.JobProcessorTest
Apache OpenEJB 4.0.0-SNAPSHOT build: 20110801-04:02
http://openejb.apache.org/
INFO - openejb.home = G:\Workspace\fullproject\openejb3\examples\async-methods
INFO - openejb.base = G:\Workspace\fullproject\openejb3\examples\async-methods
INFO - Using 'javax.ejb.embeddable.EJBContainer=true'
INFO - Configuring Service(id=Default Security Service, type=SecurityService, provider-id=Default Security Service)
INFO - Configuring Service(id=Default Transaction Manager, type=TransactionManager, provider-id=Default Transaction Manager)
INFO - Found EjbModule in classpath: g:\Workspace\fullproject\openejb3\examples\async-methods\target\classes
INFO - Beginning load: g:\Workspace\fullproject\openejb3\examples\async-methods\target\classes
INFO - Configuring enterprise application: g:\Workspace\fullproject\openejb3\examples\async-methods
INFO - Configuring Service(id=Default Singleton Container, type=Container, provider-id=Default Singleton Container)
INFO - Auto-creating a container for bean JobProcessor: Container(type=SINGLETON, id=Default Singleton Container)
INFO - Configuring Service(id=Default Managed Container, type=Container, provider-id=Default Managed Container)
INFO - Auto-creating a container for bean org.superbiz.async.JobProcessorTest: Container(type=MANAGED, id=Default Managed Container)
INFO - Enterprise application "g:\Workspace\fullproject\openejb3\examples\async-methods" loaded.
INFO - Assembling app: g:\Workspace\fullproject\openejb3\examples\async-methods
INFO - Jndi(name="java:global/async-methods/JobProcessor!org.superbiz.async.JobProcessor")
INFO - Jndi(name="java:global/async-methods/JobProcessor")
INFO - Jndi(name="java:global/EjbModule100568296/org.superbiz.async.JobProcessorTest!org.superbiz.async.JobProcessorTest")
INFO - Jndi(name="java:global/EjbModule100568296/org.superbiz.async.JobProcessorTest")
INFO - Created Ejb(deployment-id=org.superbiz.async.JobProcessorTest, ejb-name=org.superbiz.async.JobProcessorTest, container=Default Managed Container)
INFO - Created Ejb(deployment-id=JobProcessor, ejb-name=JobProcessor, container=Default Singleton Container)
INFO - Started Ejb(deployment-id=org.superbiz.async.JobProcessorTest, ejb-name=org.superbiz.async.JobProcessorTest, container=Default Managed Container)
INFO - Started Ejb(deployment-id=JobProcessor, ejb-name=JobProcessor, container=Default Singleton Container)
INFO - Deployed Application(path=g:\Workspace\fullproject\openejb3\examples\async-methods)
Tests run: 1, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 13.305 sec
Results :
Tests run: 1, Failures: 0, Errors: 0, Skipped: 0
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 21.097s
[INFO] Finished at: Wed Aug 03 22:48:26 IST 2011
[INFO] Final Memory: 13M/145M
[INFO] ------------------------------------------------------------------------
#Related Examples
For complex asynchronous processing, JavaEE's answer is MessageDrivenBean. Have a look at the simple-mdb example