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 &nbsp;
 <div class="page-header">
 <h1>CDI Interceptors

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 <p>Let'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'll throw out an AccessDeniedException.</p>

 <p>How do we mark which methods are to be intercepted? Wouldn't it be handy to annotate a method like</p>

 <pre><code>@Log
 public void aMethod(){...}
 </code></pre>

 <p>or</p>

 <pre><code>@TimeRestricted
 public void bMethod(){...}
 </code></pre>

 <p>Let's create these annotations that would "mark" a method for interception.</p>

 <pre><code>@InterceptorBinding
 @Target({ TYPE, METHOD })
 @Retention(RUNTIME)
 public @interface Log {
 }
 </code></pre>

 <p>And</p>

 <pre><code>@InterceptorBinding
 @Target({ TYPE, METHOD })
 @Retention(RUNTIME)
 public @interface TimeRestricted {
 }
 </code></pre>

 <p>Sure, you haven'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>

 <p>So here's our logging interceptor. An <code>@AroundInvoke</code> method and we are almost done.</p>

 <pre><code>@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();
     }
 }
 </code></pre>

 <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>

 <p>That done, let's annotate at class-level or method-level and have fun intercepting!</p>

 <pre><code>@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
 }
 </code></pre>

 <p>The <code>@Log</code> annotation applied at class level denotes that all the methods should be intercepted with <code>BookForAShowLoggingInterceptor</code>.</p>

 <p>Before we say "all done" there's one last thing we are left with! To enable the interceptors!</p>

 <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>

 <pre><code>&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;
 </code></pre>

 <p>By default, a bean archive has no enabled interceptors bound via interceptor
 bindings. An interceptor must be explicitly enabled by listing its class
 in the <code>beans.xml</code>.</p>

 <p>Those lines in <code>beans.xml</code> not only "enable" the interceptors, but also define the "order of execution" of the interceptors.</p>

 <p>The order in with a method is annotated has no real significance.
 Eg:</p>

 <pre><code>@TimeRestrict
 @Log
 void cMethod(){}
 </code></pre>

 <p>Here the <code>BookForAShowLoggingInterceptor</code> would be applied first and then <code>TimeBasedRestrictingInterceptor</code></p>

 <p>So now you know that the order is only determined by the order of definition in <code>beans.xml</code>. Interceptors which occur earlier in the list are called first.</p>

 <p>Also note that a method can be marked for interception by multiple interceptors by applying multiple annotations as above.</p>

 <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.... Having to annotate so much makes the code a little clumsy?</p>

 <p>No worries! Just create a custom annotation which inherits from others</p>

 <pre><code>@Inherited
 @InterceptorBinding
 @Target({ TYPE, METHOD })
 @Retention(RUNTIME)
 @Log
 @TimeRestricted
 public @interface TimeRestrictAndLog {
 }
 </code></pre>

 <p>This is interceptor binding inheritance.</p>

 <p>The code below demonstrates the many cases that we have discussed.</p>

 <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>

 <h1>The Code</h1>

 <h2>BookForAShowOneInterceptorApplied</h2>

 <p><code>BookForAShowOneInterceptorApplied</code> shows a simple <code>@Log</code> interceptor applied.</p>

 <pre><code>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>

 <h2>BookForAShowTwoInterceptorsApplied</h2>

 <p><code>BookForAShowTwoInterceptorsApplied</code> shows both <code>@Log</code> and <code>@TimeRestricted</code> being applied.</p>

 <pre><code>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>

 <h2>BookShowInterceptorBindingInheritanceExplored</h2>

 <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>

 <pre><code>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>


 <div class="page-header">&nbsp;</div>
 <h4>APIs Used</h4>
 <ul><li><a href="http://docs.oracle.com/javaee/6/api/javax/ejb/ApplicationException.html">javax.ejb.ApplicationException</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/Stateful.html">javax.ejb.Stateful</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/Interceptor.html">javax.interceptor.Interceptor</a></li>
 <li><a href="http://docs.oracle.com/javaee/6/api/javax/interceptor/InterceptorBinding.html">javax.interceptor.InterceptorBinding</a></li>
 <li><a href="http://docs.oracle.com/javaee/6/api/javax/interceptor/Interceptors.html">javax.interceptor.Interceptors</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/cdi-interceptors">cdi-interceptors</a></li>
       <li>Github <a href="https://github.com/apache/tomee/tree/trunk/examples/cdi-interceptors">cdi-interceptors</a></li>
   </ul>
 <pre>
 svn co http://svn.apache.org/repos/asf/tomee/tomee/trunk/examples/cdi-interceptors
 cd cdi-interceptors
 mvn clean install
 </pre>


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	<h1>CDI Interceptors

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	<p>Let'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'll throw out an AccessDeniedException.</p>

	<p>How do we mark which methods are to be intercepted? Wouldn't it be handy to annotate a method like</p>

	<pre><code>@Log
	public void aMethod(){...}
	</code></pre>

	<p>or</p>

	<pre><code>@TimeRestricted
	public void bMethod(){...}
	</code></pre>

	<p>Let's create these annotations that would "mark" a method for interception.</p>

	<pre><code>@InterceptorBinding
	@Target({ TYPE, METHOD })
	@Retention(RUNTIME)
	public @interface Log {
	}
	</code></pre>

	<p>And</p>

	<pre><code>@InterceptorBinding
	@Target({ TYPE, METHOD })
	@Retention(RUNTIME)
	public @interface TimeRestricted {
	}
	</code></pre>

	<p>Sure, you haven'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>

	<p>So here's our logging interceptor. An <code>@AroundInvoke</code> method and we are almost done.</p>

	<pre><code>@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();
	}
	}
	</code></pre>

	<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>

	<p>That done, let's annotate at class-level or method-level and have fun intercepting!</p>

	<pre><code>@Log
	@Stateful
	public class BookForAShowOneInterceptorApplied implements Serializable {
	private static final long serialVersionUID = 6350400892234496909L;
	public List<String> getMoviesList() {
	List<String> moviesAvailable = new ArrayList<String>();
	moviesAvailable.add("12 Angry Men");
	moviesAvailable.add("Kings speech");
	return moviesAvailable;
	}
	public Integer getDiscountedPrice(int ticketPrice) {
	return ticketPrice - 50;
	}
	// assume more methods are present
	}
	</code></pre>

	<p>The <code>@Log</code> annotation applied at class level denotes that all the methods should be intercepted with <code>BookForAShowLoggingInterceptor</code>.</p>

	<p>Before we say "all done" there's one last thing we are left with! To enable the interceptors!</p>

	<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>

	<pre><code><beans>
	<interceptors>
	<class>org.superbiz.cdi.bookshow.interceptors.BookForAShowLoggingInterceptor
	</class>
	<class>org.superbiz.cdi.bookshow.interceptors.TimeBasedRestrictingInterceptor
	</class>
	</interceptors>
	</beans>
	</code></pre>

	<p>By default, a bean archive has no enabled interceptors bound via interceptor
	bindings. An interceptor must be explicitly enabled by listing its class
	in the <code>beans.xml</code>.</p>

	<p>Those lines in <code>beans.xml</code> not only "enable" the interceptors, but also define the "order of execution" of the interceptors.</p>

	<p>The order in with a method is annotated has no real significance.
	Eg:</p>

	<pre><code>@TimeRestrict
	@Log
	void cMethod(){}
	</code></pre>

	<p>Here the <code>BookForAShowLoggingInterceptor</code> would be applied first and then <code>TimeBasedRestrictingInterceptor</code></p>

	<p>So now you know that the order is only determined by the order of definition in <code>beans.xml</code>. Interceptors which occur earlier in the list are called first.</p>

	<p>Also note that a method can be marked for interception by multiple interceptors by applying multiple annotations as above.</p>

	<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.... Having to annotate so much makes the code a little clumsy?</p>

	<p>No worries! Just create a custom annotation which inherits from others</p>

	<pre><code>@Inherited
	@InterceptorBinding
	@Target({ TYPE, METHOD })
	@Retention(RUNTIME)
	@Log
	@TimeRestricted
	public @interface TimeRestrictAndLog {
	}
	</code></pre>

	<p>This is interceptor binding inheritance.</p>

	<p>The code below demonstrates the many cases that we have discussed.</p>

	<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>

	<h1>The Code</h1>

	<h2>BookForAShowOneInterceptorApplied</h2>

	<p><code>BookForAShowOneInterceptorApplied</code> shows a simple <code>@Log</code> interceptor applied.</p>

	<pre><code>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<String> getMoviesList() {
	List<String> moviesAvailable = new ArrayList<String>();
	moviesAvailable.add("12 Angry Men");
	moviesAvailable.add("Kings speech");
	return moviesAvailable;
	}

	public Integer getDiscountedPrice(int ticketPrice) {
	return ticketPrice - 50;
	}
	}
	</code></pre>

	<h2>BookForAShowTwoInterceptorsApplied</h2>

	<p><code>BookForAShowTwoInterceptorsApplied</code> shows both <code>@Log</code> and <code>@TimeRestricted</code> being applied.</p>

	<pre><code>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<String> getMoviesList() {
	List<String> moviesAvailable = new ArrayList<String>();
	moviesAvailable.add("12 Angry Men");
	moviesAvailable.add("Kings speech");
	return moviesAvailable;
	}

	@TimeRestricted
	public Integer getDiscountedPrice(int ticketPrice) {
	return ticketPrice - 50;
	}
	}
	</code></pre>

	<h2>BookShowInterceptorBindingInheritanceExplored</h2>

	<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>

	<pre><code>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<String> getMoviesList() {
	List<String> moviesAvailable = new ArrayList<String>();
	moviesAvailable.add("12 Angry Men");
	moviesAvailable.add("Kings speech");
	return moviesAvailable;
	}

	@TimeRestrictAndLog
	public Integer getDiscountedPrice(int ticketPrice) {
	return ticketPrice - 50;
	}
	}
	</code></pre>


	<div class="page-header"> </div>
	<h4>APIs Used</h4>
	<ul><li><a href="http://docs.oracle.com/javaee/6/api/javax/ejb/ApplicationException.html">javax.ejb.ApplicationException</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/Stateful.html">javax.ejb.Stateful</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/Interceptor.html">javax.interceptor.Interceptor</a></li>
	<li><a href="http://docs.oracle.com/javaee/6/api/javax/interceptor/InterceptorBinding.html">javax.interceptor.InterceptorBinding</a></li>
	<li><a href="http://docs.oracle.com/javaee/6/api/javax/interceptor/Interceptors.html">javax.interceptor.Interceptors</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/cdi-interceptors">cdi-interceptors</a></li>
	<li>Github <a href="https://github.com/apache/tomee/tree/trunk/examples/cdi-interceptors">cdi-interceptors</a></li>
	</ul>
	<pre>
	svn co http://svn.apache.org/repos/asf/tomee/tomee/trunk/examples/cdi-interceptors
	cd cdi-interceptors
	mvn clean install
	</pre>


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