Interceptor types

One of the interesting features in CDI is that we can introduce interceptors using qualifiers. Let's define one interceptor called LoggedInterceptor, which is supposed to perform logging functionalities on a big set of CDI beans in some enterprise application:

@Interceptor 
@Logged 
public class LoggedInterceptor { 
 
    @AroundInvoke 
    public Object interceptMethod(InvocationContext ctx) throws Exception { 
        Object retValue = ctx.proceed(); 
        return "intercepted " + retValue; 
    } 
} 

Note that in this example, we have annotated the interceptor with the @Logged annotation. This is a qualifier annotation that we will define as shown earlier, in the Using qualifiers section, as follows:

@InterceptorBinding 
@Target({TYPE, METHOD}) 
@Retention(RUNTIME) 
public @interface Logged { 
} 

By annotating LoggedInterceptor with the qualifier @Logged, we can later annotate any CDI bean with the @Logged qualifier, to tell the container that we wish to use the LoggedInterceptor with that CDI bean, as follows:

@Dependent 
@Logged 
public class MyPojo { ... } 

This is equivalent to the previous example, where we annotated MyPojo with the @Interceptors annotation. However, by using the qualifier rather than the interceptor class itself, we have abstracted MyPojo from the real interceptor implementation, and thus we can later alter this class type, or replace it among deployment modes (production or testing).

All CDI interceptors defined in this way are disabled by default. To make them enabled, you should define a WEB-INF/beans.xml file as the final step, with the following XML code:

<?xml version="1.0" encoding="UTF-8"?> 
<beans xmlns="http://xmlns.jcp.org/xml/ns/javaee" 
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
       xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee          http://xmlns.jcp.org/xml/ns/javaee/beans_1_1.xsd" 
       bean-discovery-mode="annotated"> 
    <interceptors> 
        <class>com.example6.LoggedInterceptor</class> 
    </interceptors> 
</beans> 

We can also apply qualified interceptors on singular methods as follows:

@Dependent 
public class MyPojo { 
 
    @Logged 
    public String getMessage1() { 
        return "MyPojo first message!"; 
    } 
    ... 
}