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| |
| <h1>@Asynchronous @PostConstruct</h1> |
| </div> |
| </div> |
| </div> |
| <div class="row"> |
| |
| <div class="col-md-12"> |
| <div class="paragraph"> |
| <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> |
| </div> |
| <div class="paragraph"> |
| <p>The heart of this pattern is to:</p> |
| </div> |
| <div class="ulist"> |
| <ul> |
| <li> |
| <p>pass the construction <code>logic</code> to an <code>@Asynchronous</code> method via a |
| <code>java.util.concurrent.Callable</code></p> |
| </li> |
| <li> |
| <p>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></p> |
| </li> |
| </ul> |
| </div> |
| <div class="paragraph"> |
| <p>Simple and effective. The result is a faster starting application that |
| is still thread-safe.</p> |
| </div> |
| <div class="listingblock"> |
| <div class="content"> |
| <pre class="highlight"><code class="language-java" data-lang="java">package org.superbiz.asyncpost; |
| |
| import jakarta.annotation.PostConstruct; |
| import jakarta.ejb.EJB; |
| import jakarta.ejb.Lock; |
| import jakarta.ejb.LockType; |
| import jakarta.ejb.Singleton; |
| import jakarta.interceptor.AroundInvoke; |
| import jakarta.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> |
| </div> |
| </div> |
| <div class="paragraph"> |
| <p>The <code>Executor</code> is a simple pattern, useful for many things, which |
| exposes an interface functionally equivalent to |
| <code>java.util.concurrent.ExecutorService</code>, but with the underlying thread |
| pool controlled by the container.</p> |
| </div> |
| <div class="listingblock"> |
| <div class="content"> |
| <pre class="highlight"><code class="language-java" data-lang="java">package org.superbiz.asyncpost; |
| |
| import jakarta.ejb.AsyncResult; |
| import jakarta.ejb.Asynchronous; |
| import jakarta.ejb.Lock; |
| import jakarta.ejb.LockType; |
| import jakarta.ejb.Singleton; |
| import java.util.concurrent.Callable; |
| import java.util.concurrent.Future; |
| |
| @Singleton |
| @Lock(LockType.READ) |
| public class Executor { |
| |
| @Asynchronous |
| public <T> Future<T> submit(Callable<T> task) throws Exception { |
| return new AsyncResult<T>(task.call()); |
| } |
| |
| }</code></pre> |
| </div> |
| </div> |
| <div class="paragraph"> |
| <p>Finally a test case shows the usefulness of <code>@AroundInvoke</code> call in our |
| bean that calls <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 jakarta.ejb.EJB; |
| import jakarta.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> |
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