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<small><a href="./../../index.html">Home</a>&nbsp;&raquo&nbsp;<a href="./../../examples-trunk/">Examples Trunk</a>&nbsp;&raquo&nbsp;<a href="./../../examples-trunk/async-postconstruct/">Async Postconstruct</a></small><br>
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<h1>@Asynchronous @PostConstruct
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<p>Placing <code>@Asynchronous</code> on the <code>@PostConstruct</code> of an EJB is not a supported part of Java EE, but this example shows a pattern which works just as well with little effort.</p>
<p>The heart of this pattern is to:</p>
<ul>
<li>pass the construction "logic" to an <code>@Asynchronous</code> method via a <code>java.util.concurrent.Callable</code></li>
<li>ensure the bean does not process invocations till construction is complete via an <code>@AroundInvoke</code> method on the bean and the <code>java.util.concurrent.Future</code></li>
</ul>
<p>Simple and effective. The result is a faster starting application that is still thread-safe.</p>
<pre><code>package org.superbiz.asyncpost;
import javax.annotation.PostConstruct;
import javax.ejb.EJB;
import javax.ejb.Lock;
import javax.ejb.LockType;
import javax.ejb.Singleton;
import javax.interceptor.AroundInvoke;
import javax.interceptor.InvocationContext;
import java.util.concurrent.Callable;
import java.util.concurrent.Future;
import static java.util.concurrent.TimeUnit.SECONDS;
@Singleton
@Lock(LockType.READ)
public class SlowStarter {
@EJB
private Executor executor;
private Future construct;
private String color;
private String shape;
@PostConstruct
private void construct() throws Exception {
construct = executor.submit(new Callable() {
@Override
public Object call() throws Exception {
Thread.sleep(SECONDS.toMillis(10));
SlowStarter.this.color = "orange";
SlowStarter.this.shape = "circle";
return null;
}
});
}
@AroundInvoke
private Object guaranteeConstructionComplete(InvocationContext context) throws Exception {
construct.get();
return context.proceed();
}
public String getColor() {
return color;
}
public String getShape() {
return shape;
}
}
</code></pre>
<p>The <code>Executor</code> is a simple pattern, useful for many things, which exposes an interface functionaly equivalent to <code>java.util.concurrent.ExecutorService</code>, but
with the underlying thread pool controlled by the container.</p>
<pre><code>package org.superbiz.asyncpost;
import javax.ejb.AsyncResult;
import javax.ejb.Asynchronous;
import javax.ejb.Lock;
import javax.ejb.LockType;
import javax.ejb.Singleton;
import java.util.concurrent.Callable;
import java.util.concurrent.Future;
@Singleton
@Lock(LockType.READ)
public class Executor {
@Asynchronous
public &lt;T&gt; Future&lt;T&gt; submit(Callable&lt;T&gt; task) throws Exception {
return new AsyncResult&lt;T&gt;(task.call());
}
}
</code></pre>
<p>Finally a test case shows the usefulness of <code>@AroundInvoke</code> call in our bean that calls <code>construct.get()</code></p>
<pre><code>package org.superbiz.asyncpost;
import junit.framework.Assert;
import org.junit.Test;
import javax.ejb.EJB;
import javax.ejb.embeddable.EJBContainer;
public class SlowStarterTest {
@EJB
private SlowStarter slowStarter;
@Test
public void test() throws Exception {
// Start the Container
EJBContainer.createEJBContainer().getContext().bind("inject", this);
// Immediately access the fields initialized in the PostConstruct
// This will fail without the @AroundInvoke call to construct.get()
Assert.assertEquals("orange", slowStarter.getColor());
Assert.assertEquals("circle", slowStarter.getShape());
}
}
</code></pre>
<div class="page-header">&nbsp;</div>
<h4>APIs Used</h4>
<ul><li><a href="http://docs.oracle.com/javaee/6/api/javax/annotation/PostConstruct.html">javax.annotation.PostConstruct</a></li>
<li><a href="http://docs.oracle.com/javaee/6/api/javax/ejb/AsyncResult.html">javax.ejb.AsyncResult</a></li>
<li><a href="http://docs.oracle.com/javaee/6/api/javax/ejb/Asynchronous.html">javax.ejb.Asynchronous</a></li>
<li><a href="http://docs.oracle.com/javaee/6/api/javax/ejb/EJB.html">javax.ejb.EJB</a></li>
<li><a href="http://docs.oracle.com/javaee/6/api/javax/ejb/Lock.html">javax.ejb.Lock</a></li>
<li><a href="http://docs.oracle.com/javaee/6/api/javax/ejb/LockType.html">javax.ejb.LockType</a></li>
<li><a href="http://docs.oracle.com/javaee/6/api/javax/ejb/Singleton.html">javax.ejb.Singleton</a></li>
<li><a href="http://docs.oracle.com/javaee/6/api/javax/ejb/embeddable/EJBContainer.html">javax.ejb.embeddable.EJBContainer</a></li>
<li><a href="http://docs.oracle.com/javaee/6/api/javax/interceptor/AroundInvoke.html">javax.interceptor.AroundInvoke</a></li>
<li><a href="http://docs.oracle.com/javaee/6/api/javax/interceptor/AroundTimeout.html">javax.interceptor.AroundTimeout</a></li>
<li><a href="http://docs.oracle.com/javaee/6/api/javax/interceptor/InvocationContext.html">javax.interceptor.InvocationContext</a></li>
</ul>
<h3>Source</h3>
<ul>
<li>Apache <a href="http://svn.apache.org/repos/asf/tomee/tomee/trunk/examples/async-postconstruct">async-postconstruct</a></li>
<li>Github <a href="https://github.com/apache/tomee/tree/trunk/examples/async-postconstruct">async-postconstruct</a></li>
</ul>
<pre>
svn co http://svn.apache.org/repos/asf/tomee/tomee/trunk/examples/async-postconstruct
cd async-postconstruct
mvn clean install
</pre>
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