[[Container_interceptors]]
= Container interceptors

[abstract]

JBoss AS versions prior to WildFly8 allowed a JBoss specific way to
plug-in user application specific interceptors on the server side so
that those interceptors get invoked during an EJB invocation. Such
interceptors differed from the typical (portable) spec provided Jakarta EE
interceptors. The Jakarta Interceptors are expected to run after the
container has done necessary invocation processing which involves
security context propagation, transaction management and other such
duties. As a result, these Jakarta Interceptors come too late into the
picture, if the user applications have to intercept the call before
certain container specific interceptor(s) are run.

[[typical-ejb-invocation-call-path-on-the-server]]
== Typical EJB invocation call path on the server

A typical EJB invocation looks like this:

Client application

[source,java,options="nowrap"]
----
MyBeanInterface bean = lookupBean();
 
bean.doSomething();
----

The invocation on the bean.doSomething() triggers the following (only
relevant portion of the flow shown below):

1.  WildFly specific interceptor (a.k.a container interceptor) 1
2.  WildFly specific interceptor (a.k.a container interceptor) 2
3.  ....
4.  WildFly specific interceptor (a.k.a container interceptor) N
5.  User application specific Jakarta EE interceptor(s) (if any)
6.  Invocation on the EJB instance's method

The WildFly specific interceptors include the security context
propagation, transaction management and other container provided
services. In some cases, the " `container interceptors`" (let's call
them that) might even decide break the invocation flow and not let the
invocation proceed (for example: due to the invoking caller not being
among the allowed user roles who can invoke the method on the bean).

Previous versions of JBoss AS allowed a way to plug-in the user
application specific interceptors (which relied on JBoss AS specific
libraries) into this invocation flow so that they do run some
application specific logic before the control reaches step#5 above. For
example, AS5 allowed the use of JBoss AOP interceptors to do this.

As of WildFly 8, this feature was implemented.

[[configuring-container-interceptors]]
== Configuring container interceptors

As you can see from the JIRA https://issues.redhat.com/browse/AS7-5897,
one of the goals of this feature implementation was to make sure that we
don't introduce any new WildFly specific library dependencies for the
container interceptors. So we decided to allow the Jakarta Interceptors
(which are just POJO classes with lifecycle callback annotations) to be
used as container interceptors. As such you won't need any dependency on
any WildFly specific libraries. That will allow us to support this
feature for a longer time in future versions of WildFly.

Furthermore, configuring these container interceptors is similar to
configuring the Jakarta Interceptors for EJBs. In fact, it uses the same
xsd elements that are allowed in ejb-jar.xml for 3.1 version of ejb-jar
deployment descriptor.

[IMPORTANT]

Container interceptors can only be configured via deployment
descriptors. There's no annotation based way to configure container
interceptors. This was an intentional decision, taken to avoid
introducing any WildFly specific library dependency for the annotation.

Configuring the container interceptors can be done in jboss-ejb3.xml
file, which then gets placed under the META-INF folder of the EJB
deployment, just like the ejb-jar.xml. Here's an example of how the
container interceptor(s) can be configured in jboss-ejb3.xml:

.jboss-ejb3.xml

[source,xml,options="nowrap"]
----
<jboss xmlns="http://www.jboss.com/xml/ns/javaee"
       xmlns:jee="http://java.sun.com/xml/ns/javaee"
       xmlns:ci ="urn:container-interceptors:1.0">
    <jee:assembly-descriptor>
        <ci:container-interceptors>
            <!-- Default interceptor -->
            <jee:interceptor-binding>
                <ejb-name>*</ejb-name>
                <interceptor-class>org.jboss.as.test.integration.ejb.container.interceptor.ContainerInterceptorOne</interceptor-class>
            </jee:interceptor-binding>
            <!-- Class level container-interceptor -->
            <jee:interceptor-binding>
                <ejb-name>AnotherFlowTrackingBean</ejb-name>
                <interceptor-class>org.jboss.as.test.integration.ejb.container.interceptor.ClassLevelContainerInterceptor</interceptor-class>
            </jee:interceptor-binding>
            <!-- Method specific container-interceptor -->
            <jee:interceptor-binding>
                <ejb-name>AnotherFlowTrackingBean</ejb-name>
                <interceptor-class>org.jboss.as.test.integration.ejb.container.interceptor.MethodSpecificContainerInterceptor</interceptor-class>
                <method>
                    <method-name>echoWithMethodSpecificContainerInterceptor</method-name>
                </method>
            </jee:interceptor-binding>
            <!-- container interceptors in a specific order -->
            <jee:interceptor-binding>
                <ejb-name>AnotherFlowTrackingBean</ejb-name>
                <interceptor-order>
                    <interceptor-class>org.jboss.as.test.integration.ejb.container.interceptor.ClassLevelContainerInterceptor</interceptor-class>
                    <interceptor-class>org.jboss.as.test.integration.ejb.container.interceptor.MethodSpecificContainerInterceptor</interceptor-class>
                    <interceptor-class>org.jboss.as.test.integration.ejb.container.interceptor.ContainerInterceptorOne</interceptor-class>
                </interceptor-order>
                <method>
                    <method-name>echoInSpecificOrderOfContainerInterceptors</method-name>
                </method>
            </jee:interceptor-binding>
        </ci:container-interceptors>
    </jee:assembly-descriptor>
</jboss>
----

* The usage of urn:container-interceptors:1.0 namespace which allows the
container-interceptors elements to be configured
* The container-interceptors element which contain the interceptor
bindings
* The interceptor bindings themselves are the same elements as what the
EJB3.1 xsd allows for standard Jakarta Interceptors
* The interceptors can be bound either to all EJBs in the deployment
(using the * wildcard) or individual bean level (using the specific
EJB name) or at specific method level for the EJBs.

[IMPORTANT]

The xsd for the urn:container-interceptors:1.0 namespace is available
here
https://github.com/wildfly/wildfly/blob/main/ejb3/src/main/resources/schema/jboss-ejb-container-interceptors_1_0.xsd

The interceptor classes themselves are simple POJOs and use the
`@javax.annotation.AroundInvoke` to mark the around invoke method which
will get invoked during the invocation on the bean. Here's an example of
the interceptor:

.Example of container interceptor

[source,java,options="nowrap"]
----
public class ClassLevelContainerInterceptor {
    @AroundInvoke
    private Object iAmAround(final InvocationContext invocationContext) throws Exception {
        return this.getClass().getName() + " " + invocationContext.proceed();
    }
}
----

[[container-interceptor-positioning-in-the-interceptor-chain]]
== Container interceptor positioning in the interceptor chain

The container interceptors configured for a EJB are guaranteed to be run
before the WildFly provided security interceptors, transaction
management interceptors and other such interceptors thus allowing the
user application specific container interceptors to setup any relevant
context data before the invocation proceeds.

[[semantic-difference-between-container-interceptors-and-Jakarta-Interceptors-api]]
== Semantic difference between container interceptor(s) and Jakarta Interceptors API

Although the container interceptors are modeled to be similar to the
Jakarta Interceptors, there are some differences in the API semantics.
One such difference is that invoking on
javax.interceptor.InvocationContext.getTarget() method is illegal for
container interceptors since these interceptors are invoked way before
the EJB components are setup or instantiated.

[[testcase]]
== Testcase

This testcase in the WildFly codebase can be used for reference for
implementing container interceptors in user applications
https://github.com/wildfly/wildfly/blob/main/testsuite/integration/basic/src/test/java/org/jboss/as/test/integration/ejb/container/interceptor/ContainerInterceptorsTestCase.java

NOTE: References in this document to Enterprise JavaBeans(EJB) refer to the Jakarta Enterprise Beans unless otherwise noted.
