EJB3 With WebWork | {"Mat's Random Thoughts"}

The letters ‘E J B’ cause me to slouch back and say “oh no…”. But after a few encouraging words to myself, I gave it a shot. If you look at my previous blog on WebWork you will see that WebWork was used as the web-tier framework and Spring was used to manage the business/service tier. On the service tier there existed a ‘TimeService’ which would (you are right) return the time of the day. One WebWork action, named Timer, would “talk” to the business tier to get the time. WebWork can be configured to inject Spring objects into the action. That is the mechanism I used to get the job done there.

Now I decided to use the exact same sample in the EJB example here.Instead of the Spring based service tier I wrote up the service tier as EJB (only stateless sessions beans). My aim was to inject the EJB service into the WebWork action. There is no Spring in this example.Spring is gone. I am neither from the Spring camp or the EJB3 camp. I am from ‘lets get the job done camp’. And with EJB3 I do see a good alternate programming model. Its all dependency injection in EJB3 so it will smell and feel a little like Spring. BTW I ran this example on JBoss 4.0.5.

Here is the service interface for the time service.

 package com.aver.service.timer;
 public interface TimeService {
      public String getTime();
 }

package com.aver.service.timer;

public interface TimeService {

public String getTime();

}

And here is the stateless session bean implementation of the service.As you can see its clearly a POJO. No pesky interfaces and callbacks to implement. Here is where it smells and feels like Spring (or any other decent IOC engine).

 package com.aver.service.timer;
 import java.text.SimpleDateFormat;
 import java.util.Calendar;
 import javax.ejb.Local;
 import javax.ejb.Stateless;
 @Stateless
 @Local(TimeService.class)
 public class TimeServiceBean implements TimeService {
      public String getTime() {
           SimpleDateFormat formatter = new SimpleDateFormat("MM/dd/yyyy HH:mm:ss");
           return "EJB3-SSB-" + formatter.format(Calendar.getInstance().getTime());
      }
 }

package com.aver.service.timer;

import java.text.SimpleDateFormat;

import java.util.Calendar;

import javax.ejb.Local;

import javax.ejb.Stateless;

@Stateless

@Local(TimeService.class)

public class TimeServiceBean implements TimeService {

public String getTime() {

SimpleDateFormat formatter = new SimpleDateFormat("MM/dd/yyyy HH:mm:ss");

return "EJB3-SSB-" + formatter.format(Calendar.getInstance().getTime());

}

The only thing that tells me this is an EJB is the annotations. This is marked as a stateless session bean with a local interface of TimeService.

Now lets see the Timer action class in the web tier. This is the WebWork action class.

 package com.aver.web;
 import com.aver.service.timer.TimeService;
 import com.aver.web.annotation.InjectService;
 import com.opensymphony.xwork.ActionSupport;
 public class Timer extends ActionSupport {
      private String userName;
      private String message;
      @InjectService
      TimeService timeService;
      public String getTime() {
           message = timeService.getTime();
           return SUCCESS;
      }
      public String askForTime() {
           return SUCCESS;
      }
      public String getMessage() {
           return message;
      }
      public String getUserName() {
           return userName;
      }
      public void setUserName(String userName) {
           this.userName = userName;
      }
 }

package com.aver.web;

import com.aver.service.timer.TimeService;

import com.aver.web.annotation.InjectService;

import com.opensymphony.xwork.ActionSupport;

public class Timer extends ActionSupport {

private String userName;

private String message;

@InjectService

TimeService timeService;

public String getTime() {

message = timeService.getTime();

return SUCCESS;

}

public String askForTime() {

return SUCCESS;

}

public String getMessage() {

return message;

}

public String getUserName() {

return userName;

}

public void setUserName(String userName) {

this.userName = userName;

}

As you can see its really simple. Wait … what is the @InjectService annotation here. You can see that in the getTime method I call out to the service to get the time. In the WebWork+Springblog I could depend on the WebWork+Spring integration for the service to be injected in. Not any more. Now my TimeService is an EJB. I could do away with the @InjectService and instead directly lookup the JNDIcontext for the EJB. But that would not be a good architectural approach. You want to consolidate the service locator feature into one place. With the introduction of annotations in Java 5 you now have apowerful way of moving such features into annotations. Note in EJB3 you can do dependency injection within and between container managed objects. The Timer class is not an EJB3 managed object. So you are on your own.

Here is the annotation.

 package com.aver.web.annotation;
 import java.lang.annotation.ElementType;
 import java.lang.annotation.Retention;
 import java.lang.annotation.RetentionPolicy;
 import java.lang.annotation.Target;
 @Retention(RetentionPolicy.RUNTIME)
 @Target(ElementType.FIELD)
 public @interface InjectService {
 }

package com.aver.web.annotation;

import java.lang.annotation.ElementType;

import java.lang.annotation.Retention;

import java.lang.annotation.RetentionPolicy;

import java.lang.annotation.Target;

@Retention(RetentionPolicy.RUNTIME)

@Target(ElementType.FIELD)

public @interface InjectService {

}

This is a marker annotation used to mark where service injection is required at the field level. I am not a fan of setter injection for such things. Why write a setTimeService method just to have injection done there and a false sense of OO compliance?

Finally, to inject the service I wrote up a quick WebWork interceptor that looked up the JNDI context and injected the desired service. This code can be more robust, but this works.

 package com.aver.web;
 import static java.lang.System.out;
 import java.lang.reflect.Field;
 import javax.naming.Context;
 import javax.naming.InitialContext;
 import javax.naming.NamingException;
 import com.aver.service.timer.TimeService;
 import com.aver.web.annotation.InjectService;
 import com.opensymphony.xwork.ActionInvocation;
 import com.opensymphony.xwork.interceptor.AroundInterceptor;
 public class ServiceInjector extends AroundInterceptor {
      protected void after(ActionInvocation arg0, String arg1) throws Exception {
      }
      protected void before(ActionInvocation invocation) throws Exception {
           Object action = invocation.getAction();
           Class clazz = action.getClass();
           out.println(action.getClass().getName());
           for (Field field : clazz.getDeclaredFields()) {
                out.println("&gt;&gt;&gt; " + field.getName());
                if (field.isAnnotationPresent(InjectService.class)) {
                     out.println("FIELD " + field.getName()
                               + " IS ANNOTATED WITH @InjectService");
                     field.set(action, getService(field.getType().getName()));
                }
           }
      }
      private Object getService(String serviceJndiName) {
           Context ctx;
           try {
                ctx = new InitialContext();
                return ctx.lookup(serviceJndiName);
           } catch (NamingException e) {
                e.printStackTrace();
           }
           return null;
      }
 }

package com.aver.web;

import static java.lang.System.out;

import java.lang.reflect.Field;

import javax.naming.Context;

import javax.naming.InitialContext;

import javax.naming.NamingException;

import com.aver.service.timer.TimeService;

import com.aver.web.annotation.InjectService;

import com.opensymphony.xwork.ActionInvocation;

import com.opensymphony.xwork.interceptor.AroundInterceptor;

public class ServiceInjector extends AroundInterceptor {

protected void after(ActionInvocation arg0, String arg1) throws Exception {

}

protected void before(ActionInvocation invocation) throws Exception {

Object action = invocation.getAction();

Class clazz = action.getClass();

out.println(action.getClass().getName());

for (Field field : clazz.getDeclaredFields()) {

out.println(">>> " + field.getName());

if (field.isAnnotationPresent(InjectService.class)) {

out.println("FIELD " + field.getName()

+ " IS ANNOTATED WITH @InjectService");

field.set(action, getService(field.getType().getName()));

}

private Object getService(String serviceJndiName) {

Context ctx;

try {

ctx = new InitialContext();

return ctx.lookup(serviceJndiName);

} catch (NamingException e) {

e.printStackTrace();

}

return null;

}

To configure the interceptor, update the xwork.xml file as follows.

 .. other stuff ...
 &lt;interceptors&gt;
  &lt;interceptor name="appUserInterceptor" class="com.aver.web.ExecutionTimeInterceptor"/&gt;
  &lt;interceptor name="serviceInjector" class="com.aver.web.ServiceInjector"/&gt;
  &lt;interceptor-stack name="appInterceptorStack"&gt;
   &lt;interceptor-ref name="serviceInjector"/&gt;
   &lt;interceptor-ref name="appUserInterceptor"/&gt;
   &lt;interceptor-ref name="defaultStack"/&gt;
  &lt;/interceptor-stack&gt;
 &lt;/interceptors&gt;
 &lt;default-interceptor-ref name="appInterceptorStack"/&gt;
 .. other stuff ...

.. other stuff ...

<interceptor-stack name="appInterceptorStack">

<interceptor-ref name="serviceInjector"/>

<interceptor-ref name="appUserInterceptor"/>

<interceptor-ref name="defaultStack"/>

</interceptor-stack>

</interceptors>

<default-interceptor-ref name="appInterceptorStack"/>

.. other stuff ...

Compile and deploy the application. The download jar contains the full source and the ant script to create the ear file. Now when you hit the URL localhost:9090/webworks/askfortime.jsp you will see.

Enter name and hit ‘Get Time’. You should now see:

To download the code click here. The code is missing all of the external jar files for EJB3. This project was built with JBoss. The generated ear file myapp.ear will contain

– service.ejb3 (this is a jar file named with .ejb3 extension so that JBoss knows to look inside for all EJB3 beans).
– webworks.war (all of the code and libraries for the WebWork supported client tier).
– META-INF/application.xml (contains references to the web module and ejb module)

Also I had the following JBoss libraries in my eclipse/Ant classpath for compilation. Don’t package these with the ear file please.

jboss-4.0.5.GA/server/all/deploy/ejb3.deployer/ejb3-persistence.jar
jboss-4.0.5.GA/server/all/deploy/ejb3.deployer/jboss-ejb3x.jar
jboss-4.0.5.GA/server/all/deploy/ejb3.deployer/jboss-ejb3.jar

Other than this I had the following jars for WebWork support in the war file. You can drop them in the lib folder of the project:

xwork.jar
webwork-2.2.4.jar
tiles-core.jar
rife-continuations.jar
oscore.jar
ognl.jar
freemarker.jar
commons-logging-1.0.4.jar
commons-digester-1.6.jar
commons-beanutils-1.7.0.jar

I started JBoss with run.sh -c all.

As you can see its clearly possible to build a system around EJB3 (this is for those of us for whom EJB1 and 2 left a bad taste in our mouths).For those starting new from EJB3 … it does not matter.