GWT with EJB

A better and updated version is maintained here (http://grprakash.googlepages.com/gwtwithejb).
In this post, I thought I’ll explain how to use GWT with EJB. GWT addresses the web layer and EJB the middle layer, its natural to use both of them to have a neat J2ee app.

I assume that you know how to create EJB project and Web project with Googlipse. For the second one, I’ve written a post here.

If you are an advanced EJB developer and have used GWT for a while, “Use the RemoteServiceImpl as a EJB client and continue in the as usual way”. If you are not, then the rest of the post is for you.

What we are trying now is to have a text box in the web page and a button. When you key in a person’s name there and press the button, it will show the age of the person.

The first step is to create a Stateless Session Bean. The Remote & Home interface will look like this:

public interface AgeServiceEjb
extends EJBObject, Remote {

public int getAge(String name);
}

public interface AgeServiceHome
extends EJBHome {
public AgeService create()
throws …;
}

The EJB looks something like:

public class AgeServiceBean
implements SessionBean {

//All EJB members here
public int getAge(String name){

int age;

if(name.equals(“Pranni”))
age = 18; //Pranni is always 18🙂
else if(name.equals(“Bill Gates”))
age = 51;
else
age = 40; // default value

return age;
}
}

I opted for a very simple implementation. Of course you have do the normal way of contacting the Data Layer. Use Entity beans or try plain JDBC or use Hibernate. Check whether name is null or not, throw a NameNotFound exception. Its the plain old normal EJB code. GWT never restricts anything here. If you already have some EJB, exposing it to a servlet or a swing client, very well, you can reuse that also.

Now let us create a Remote service in the Web layer.

The GWT’s RemoteService is very similar to the RemoteInterface of EJB:

public interface AgeServiceGwt
extends RemoteService {

public int getAge(String name);

// Other members Util, SERVICE_URI etc
}

The RemoteService’s Impl is the key which connects GWT and EJB:

public interface AgeServiceGwtImpl
extends RemoteServiceServlet
implements AgeServiceGwt{

public int getAge(String name){
Context ctx = new InitialContext();
AgeServiceHome hme =
(AgeServiceHome)ctx.lookup(“<JNDI name>”);
AgeServiceEjb ageService = hme.create();
return ageService.getAge(name);
}
}

You can do all the normal EJB client stuff here. Add parameters to create initial context, configure the JNDI name, cache the home interface, etc. If you have ever used JSP/servlets calling EJB code, think it in the same way. Treat the Impl class as a servlet (in fact it is!) and do the usual way.

Common problems:

  • How do I deploy the EJB in the GWT’s embedded Tomcat server?


You can’t. In fact you can’t deploy it even on an external Tomcat. Its just a web container. You need an app server like WebLogic or JBoss

  • How do I create a EAR file?


Create an EAR project and add these projects (EJB & Web) to it. Select File->Export->Export as EAR file

  • Can I deploy the application in an app server and still debug in hosted mode?


Yes. Look at “Deploying to an external server” in the GWT tutorial. Its the same way.

2 Responses to “GWT with EJB”

  1. aparup Says:

    I really liked it. Very good job!

  2. Mateusz Szczap Says:

    Is it possible to expose domain objects as well. In your example the value that is returned to client is simply an integer. Is is possible to return let’s say typical domain model object, such as customer, address, etc?

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s


%d bloggers like this: