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<h1>CDI Interceptors</h1>
</div>
</div>
</div>
<div class="row">
<div class="col-md-12">
<div id="preamble">
<div class="sectionbody">
<div class="paragraph">
<p>Let&#8217;s write a simple application that would allow us to book tickets for a movie show. As with all applications, logging is one cross-cutting concern that we have. Apart from that, there are some methods in our application, that can be accessed only in the working hours. If accessed at non-working-hours we&#8217;ll throw out an AccessDeniedException.</p>
</div>
<div class="paragraph">
<p>How do we mark which methods are to be intercepted? Wouldn&#8217;t it be handy to annotate a method like</p>
</div>
<div class="literalblock">
<div class="content">
<pre>@Log
public void aMethod(){...}</pre>
</div>
</div>
<div class="paragraph">
<p>or</p>
</div>
<div class="literalblock">
<div class="content">
<pre>@TimeRestricted
public void bMethod(){...}</pre>
</div>
</div>
<div class="paragraph">
<p>Let&#8217;s create these annotations that would "mark" a method for interception.</p>
</div>
<div class="literalblock">
<div class="content">
<pre>@InterceptorBinding
@Target({ TYPE, METHOD })
@Retention(RUNTIME)
public @interface Log {
}</pre>
</div>
</div>
<div class="paragraph">
<p>And</p>
</div>
<div class="literalblock">
<div class="content">
<pre>@InterceptorBinding
@Target({ TYPE, METHOD })
@Retention(RUNTIME)
public @interface TimeRestricted {
}</pre>
</div>
</div>
<div class="paragraph">
<p>Sure, you haven&#8217;t missed the <code>@InterceptorBinding</code> annotation above! Now that our custom annotations are created, lets attach them (or to use a better term for it, "bind them") to interceptors.</p>
</div>
<div class="paragraph">
<p>So here&#8217;s our logging interceptor. An <code>@AroundInvoke</code> method and we are almost done.</p>
</div>
<div class="literalblock">
<div class="content">
<pre>@Interceptor
@Log //binding the interceptor here. now any method annotated with @Log would be intercepted by logMethodEntry
public class BookForAShowLoggingInterceptor implements Serializable {
private static final long serialVersionUID = 8139854519874743530L;
private Logger logger = Logger.getLogger("BookForAShowApplicationLogger");
@AroundInvoke
public Object logMethodEntry(InvocationContext ctx) throws Exception {
logger.info("Before entering method:" + ctx.getMethod().getName());
InterceptionOrderTracker.getMethodsInterceptedList().add(ctx.getMethod().getName());
InterceptionOrderTracker.getInterceptedByList().add(this.getClass().getSimpleName());
return ctx.proceed();
}
}</pre>
</div>
</div>
<div class="paragraph">
<p>Now the <code>@Log</code> annotation we created is bound to this interceptor. (Likewise we bind <code>@TimeRestrict</code> for <code>TimeBasedRestrictingInterceptor</code>. See links below for source)</p>
</div>
<div class="paragraph">
<p>That done, let&#8217;s annotate at class-level or method-level and have fun intercepting!</p>
</div>
<div class="literalblock">
<div class="content">
<pre>@Log
@Stateful
public class BookForAShowOneInterceptorApplied implements Serializable {
private static final long serialVersionUID = 6350400892234496909L;
public List&lt;String&gt; getMoviesList() {
List&lt;String&gt; moviesAvailable = new ArrayList&lt;String&gt;();
moviesAvailable.add("12 Angry Men");
moviesAvailable.add("Kings speech");
return moviesAvailable;
}
public Integer getDiscountedPrice(int ticketPrice) {
return ticketPrice - 50;
}
// assume more methods are present
}</pre>
</div>
</div>
<div class="paragraph">
<p>The <code>@Log</code> annotation applied at class level denotes that all the methods should be intercepted with <code>BookForAShowLoggingInterceptor</code>.</p>
</div>
<div class="paragraph">
<p>Before we say "all done" there&#8217;s one last thing we are left with! To enable the interceptors!</p>
</div>
<div class="paragraph">
<p>Lets quickly put up a <code>beans.xml</code> file like the following in <code>src/main/resources/META-INF/beans.xml</code>:</p>
</div>
<div class="literalblock">
<div class="content">
<pre>&lt;beans&gt;
&lt;interceptors&gt;
&lt;class&gt;org.superbiz.cdi.bookshow.interceptors.BookForAShowLoggingInterceptor
&lt;/class&gt;
&lt;class&gt;org.superbiz.cdi.bookshow.interceptors.TimeBasedRestrictingInterceptor
&lt;/class&gt;
&lt;/interceptors&gt;
&lt;/beans&gt;</pre>
</div>
</div>
<div class="paragraph">
<p>By default, a bean archive has no enabled interceptors; an interceptor must be explicitly enabled by listing its class
in the <code>beans.xml</code>.</p>
</div>
<div class="paragraph">
<p>The order of the interceptor annotations has no real significance.
Eg:</p>
</div>
<div class="literalblock">
<div class="content">
<pre>@TimeRestrict
@Log
void cMethod(){}</pre>
</div>
</div>
<div class="paragraph">
<p>It is the <code>interceptor</code> elements in <code>beans.xml</code> that not only "enable" the interceptors, but also define the "order of execution" of the interceptors. In this case the <code>BookForAShowLoggingInterceptor</code> would be applied first and then <code>TimeBasedRestrictingInterceptor</code></p>
</div>
<div class="paragraph">
<p>So now you know that the order is only determined by the order within the <code>interceptors</code> element within the <code>beans.xml</code>. The rule is simple, interceptors which occur earlier in the list are called first.</p>
</div>
<div class="paragraph">
<p>Also note that a method can be marked for interception using multiple interceptors by applying multiple annotations as above.</p>
</div>
<div class="paragraph">
<p>This brings us to another question. In the above case there were two interceptors applied together. What if I would require about 4 such interceptors that would go along&#8230;&#8203;. Having to annotate so much makes the code a little clumsy?</p>
</div>
<div class="paragraph">
<p>No worries! Just create a custom annotation which inherits from others</p>
</div>
<div class="literalblock">
<div class="content">
<pre>@Inherited
@InterceptorBinding
@Target({ TYPE, METHOD })
@Retention(RUNTIME)
@Log
@TimeRestricted
public @interface TimeRestrictAndLog {
}</pre>
</div>
</div>
<div class="paragraph">
<p>This is interceptor binding inheritance.</p>
</div>
<div class="paragraph">
<p>The code below demonstrates the many cases that we have discussed.</p>
</div>
<div class="paragraph">
<p>Not to forget, the old style binding with <code>@Interceptors(WhicheverInterceptor.class)</code> is also supported. Have a look at <code>BookForAShowOldStyleInterceptorBinding</code> where the comments explain how the newer way discussed above is better.</p>
</div>
</div>
</div>
<div class="sect1">
<h2 id="_the_code">The Code</h2>
<div class="sectionbody">
<div class="sect2">
<h3 id="_bookforashowoneinterceptorapplied">BookForAShowOneInterceptorApplied</h3>
<div class="paragraph">
<p><code>BookForAShowOneInterceptorApplied</code> shows a simple <code>@Log</code> interceptor applied.</p>
</div>
<div class="listingblock">
<div class="content">
<pre class="highlight"><code class="language-java" data-lang="java">package org.superbiz.cdi.bookshow.beans;
import org.superbiz.cdi.bookshow.interceptorbinding.Log;
import javax.ejb.Stateful;
import java.io.Serializable;
import java.util.ArrayList;
import java.util.List;
@Log
@Stateful
public class BookForAShowOneInterceptorApplied implements Serializable {
private static final long serialVersionUID = 6350400892234496909L;
public List&lt;String&gt; getMoviesList() {
List&lt;String&gt; moviesAvailable = new ArrayList&lt;String&gt;();
moviesAvailable.add("12 Angry Men");
moviesAvailable.add("Kings speech");
return moviesAvailable;
}
public Integer getDiscountedPrice(int ticketPrice) {
return ticketPrice - 50;
}
}</code></pre>
</div>
</div>
</div>
<div class="sect2">
<h3 id="_bookforashowtwointerceptorsapplied">BookForAShowTwoInterceptorsApplied</h3>
<div class="paragraph">
<p><code>BookForAShowTwoInterceptorsApplied</code> shows both <code>@Log</code> and <code>@TimeRestricted</code> being applied.</p>
</div>
<div class="listingblock">
<div class="content">
<pre class="highlight"><code class="language-java" data-lang="java">package org.superbiz.cdi.bookshow.beans;
import org.superbiz.cdi.bookshow.interceptorbinding.Log;
import org.superbiz.cdi.bookshow.interceptorbinding.TimeRestricted;
import javax.ejb.Stateful;
import java.io.Serializable;
import java.util.ArrayList;
import java.util.List;
@Log
@Stateful
public class BookForAShowTwoInterceptorsApplied implements Serializable {
private static final long serialVersionUID = 6350400892234496909L;
public List&lt;String&gt; getMoviesList() {
List&lt;String&gt; moviesAvailable = new ArrayList&lt;String&gt;();
moviesAvailable.add("12 Angry Men");
moviesAvailable.add("Kings speech");
return moviesAvailable;
}
@TimeRestricted
public Integer getDiscountedPrice(int ticketPrice) {
return ticketPrice - 50;
}
}</code></pre>
</div>
</div>
</div>
<div class="sect2">
<h3 id="_bookshowinterceptorbindinginheritanceexplored">BookShowInterceptorBindingInheritanceExplored</h3>
<div class="paragraph">
<p><code>BookShowInterceptorBindingInheritanceExplored</code> shows how <code>@TimeRestrictAndLog</code> (interceptor-binding-inheritance) can be used as an alternative for annotating a method with multiple annotations explicitly.</p>
</div>
<div class="listingblock">
<div class="content">
<pre class="highlight"><code class="language-java" data-lang="java">package org.superbiz.cdi.bookshow.beans;
import org.superbiz.cdi.bookshow.interceptorbinding.TimeRestrictAndLog;
import javax.ejb.Stateful;
import java.io.Serializable;
import java.util.ArrayList;
import java.util.List;
@Stateful
public class BookShowInterceptorBindingInheritanceExplored implements Serializable {
private static final long serialVersionUID = 6350400892234496909L;
public List&lt;String&gt; getMoviesList() {
List&lt;String&gt; moviesAvailable = new ArrayList&lt;String&gt;();
moviesAvailable.add("12 Angry Men");
moviesAvailable.add("Kings speech");
return moviesAvailable;
}
@TimeRestrictAndLog
public Integer getDiscountedPrice(int ticketPrice) {
return ticketPrice - 50;
}
}</code></pre>
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