# EJB 3.1 And REST - The Lightweight Hybrid

The Local / Remote interfaces in EJB 3.1 are optional. You can still, however, expose a Session bean as a RESTFul (JSR-311) service.

package com.abien.patterns.business.rest.boundary;

import com.abien.patterns.business.rest.control.Service;
import javax.ejb.EJB;
import javax.ejb.Stateless;
import javax.ws.rs.GET;
import javax.ws.rs.Path;

@Stateless
@Path("current")
public class ServiceFacade {

    @EJB
    Service service;

    @GET
    public String getDate(){
        return service.getCurrentDate().toString();
    }

}



The Service is just another, usual, @Local bean:

@Stateless
public class Service {

    public Date getCurrentDate(){
        return new Date();
    }
}

A ServiceFacade becomes available via REST, just denoting it with the JAR-RS annotations. Its both an EJB 3.1 and a REST-resource - it is available under http://localhost:8080/EJBRestHybrid/resources/current (tested with Glassfish v3 preview). It will return the current time as String (Mon Jun 29 08:19:32 CEST 2009). The additional @Stateless has the following advantages:Injection capabilities: you can easily inject other EJBs, EntityManagers, JMS-resources, DataSources or JCA connectorsTransactions: all changes made in a REST-call will be automatically and transparently synchronized with the databaseSingle threading programming model -> the old EJB goodness.Monitoring: an EJB is visible in JMXThrottling: its easy to restrict the concurrency of an EJB using ThreadPools or bean poolsVendor-independence: EJB 3 runs on multiple containers, without any modification (and without any XML in particular :-))Exposing a protocol-neutral ServiceFacade directly via REST can make it REST-dependent. E.g. you may pass JAXB-enabled classes as parameters / return - values. It will be hard then to expose the ServiceFacade through other channels. On the other hand - if REST is all you need, it is the simplest and leanest approach. There are no additional libraries needed - everything is already included in a Java EE 6 container (in Glassfish v3 the whole EJB 3.1 container is < 1 MB...). The whole example project (tested with Netbeans 6.7rc3 and Glassfish v3 Preview) with source code was pushed into http://kenai.com/projects/javaee-patterns. In Netbeans 6.7 you will have to enable Glassfish v3 capabilities. If you are using vi or emacs :-), you will have to include the Java EE 6 API to the classpath.[This sample is based on the ServiceFacade pattern from the "Real World Java EE Patterns" book]