Web Services support

EJBs provide seamless support for exposing business functionality as web services - REST and SOAP being two variants. The annotations responsible to this magic are

  • @Path
  • @WebService

@Path and @WebService are not a part of the EJB specification. They belong to JSR 311 (JAX-RS) and JSR 181 (JAX-WS) specifications respectively

@WebService

The real beauty lies in the fact that session beans can be decorated with this annotation and the EJB container automagically exposes their functionality as SOAP based web services.

package ejbap.ws;

import java.util.Date;
import javax.ejb.Stateless;
import javax.jws.WebMethod;
import javax.jws.WebParam;
import javax.jws.WebResult;
import javax.jws.WebService;


@Stateless
@WebService
public class EJBasSOAPWebService {

    @WebMethod
    public String getDate(){
        return new Date().toString();
    }

    @WebMethod
    @WebResult(name = "response")
    public String greet(@WebParam String greeting){
        return greeting + " World !";
    }
}

As you might have already noticed in the above example, JSR 181 exposes other annotations like @WebMethod, @WebResult, @WebParam etc. to help further refine your web service methods.

In order to gain more flexibility and ease of extension, a better approach would be to provide a layer of indirection with the help of an additional session bean

  • Delegate actual service calls to an injected EJB instance
  • Avoid tight coupling between your Web Service layer and EJB business tier logic

@Path

REST web services cannot lag behind SOAP. Can they ! Java EE provides you the ability to use the @Path annotation to expose session beans over a RESTful interface. I guess you have already realized that the idea is not very different compared to the SOAP based web service interface approach.

package ejbap.ws;

import javax.ejb.Stateless;
import javax.ws.rs.GET;
import javax.ws.rs.POST;
import javax.ws.rs.Path;
import javax.ws.rs.QueryParam;


@Stateless
@Path("test")
public class EJBonREST {

    @GET
    public String get(@QueryParam("name") String propName){
        return System.getProperty(propName);
    }

    @POST
    public String greet(final String greeting){
        return greeting + " World !";
    }

}

Similar to SOAP based approach

  • Avoid coupling b/w your EJB and RESTful interface by introducing another layer of abstraction/facade
  • Continue to enrich your EJB methods with additional annotations from the JAX-RS API e.g. @PUT, @DELETE, @PathParam etc.

Up ahead...

The next chapter covers exception handling and its one and only annotation

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