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<h1>@Asynchronous @PostConstruct</h1>
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<div class="paragraph">
<p>Colocar <code>@ Asynchronous</code> no <code>@ PostConstruct</code> de um EJB não é uma
parte suportada do Java EE, mas neste exemplo mostraremos um padrão que funciona
tão bem com pouco esforço.</p>
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<div class="paragraph">
<p>O coração deste padrão é para:</p>
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<ul>
<li>
<p>passar a construção <code> logic</code> para um método <code>@ Asynchronous</code> através de um
<code>java.util.concurrent.Callable</code></p>
</li>
<li>
<p>garantir que o bean não processe invocações até que a construção seja
completada através de um método <code>@ AroundInvoke</code> no bean e no
<code>java.util.concurrent.Future</code></p>
</li>
</ul>
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<div class="paragraph">
<p>Simples e efetiva. O resultado é um inicialização rápida da aplicação que ainda é thread-safe.</p>
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<pre class="highlight"><code class="language-java" data-lang="java">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>
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<div class="paragraph">
<p>O <code>Executor</code> é um simples padrão, útil para muitas coisas, que expõe uma
interface funcionalmente equivalente a <code>java.util.concurrent.ExecutorService</code>,
mas com o conjunto de encadeamentos subjacente controlado pelo contêiner.</p>
</div>
<div class="listingblock">
<div class="content">
<pre class="highlight"><code class="language-java" data-lang="java">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>
</div>
</div>
<div class="paragraph">
<p>Finalmente um caso de teste mostrando a utilidade do <code>@AroundInvoke</code> chamado no nosso
bean que chama o <code>construct.get()</code></p>
</div>
<div class="listingblock">
<div class="content">
<pre class="highlight"><code class="language-java" data-lang="java">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 {
// Inicia o Container
EJBContainer.createEJBContainer().getContext().bind("inject", this);
// Imaediatamente acessa os campos inicializado no PostConstruct
// Isso falhará sem a chamada @AroundInvoke para construct.get ()
Assert.assertEquals("orange", slowStarter.getColor());
Assert.assertEquals("circle", slowStarter.getShape());
}
}</code></pre>
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