Question

Sorry, this questions sounds silly, but after developing some of my RESTful services using Jersey, I asked myself the question — If REST is just an architecture, and not a protocol like SOAP, why do we need a specification like JAX-RS?

I actually googled for questions like “What is the difference between servlets and RESTful services over HTTP” and to sum up the community answers, I got:

1. RESTful service development (on Jersey) is an architecture, which inherently uses servlets.
2. JAX-RS compliant tools like Jersey provide easy marshalling-unmarshalling of XML/JSON data, helping the developers.
3. REST helps us use GET/POST/PUT/DELETE in a fashion that is far efficient than normal servlets.

According to these answers, I guess if I write a servlet which uses JAXB (for dealing with automatic serialization), and I efficiently use GET/POST/PUT/DELETE in my servlet code, I don’t use a tool like Jersey, and hence JAX-RS.

I know I am terribly wrong passing this statement, please correct me.

PS: This doubt actually came in when I had to develop some RESTful services in PHP. After going on through some of the RESTful PHP codes, I realized they are just the same old PHP scripts, with some helper methods for handling XML/JSON.

Answer 1

Why use JAX-RS / Jersey?

Short Answer

Because it makes the development of RESTful services easier.

Long Answer

JAX-RS is a standard that makes it easy to create a RESTful service that can be deployed to any Java application server: GlassFish, WebLogic, WebSphere, JBoss, etc.

JAX-RS is part of Java EE, and when JAX-RS is used with other Java EE technologies it becomes even easier to create your RESTful service:

• EJB – A session bean is used as the service implementation and also handles the transaction semantics.
• JAX-RS – Used to expose the session bean as a RESTful service
• JPA – Used to persist the POJOs to the database. Note how the EntityManager is injected onto the session bean.
• JAXB – Used to convert the POJO to/from XML (in GlassFish it can also be used to convert the POJO to/from JSON). JAX-RS by default handles the interaction with the JAXB implementation.

Sample JAX-RS Service

package org.example;

import java.util.List;

import javax.ejb.*;
import javax.persistence.*;
import javax.ws.rs.*;
import javax.ws.rs.core.MediaType;

@Stateless
@LocalBean
@Path("/customers")
public class CustomerService {

    @PersistenceContext(unitName="CustomerService",
                        type=PersistenceContextType.TRANSACTION)
    EntityManager entityManager;

    @POST
    @Consumes(MediaType.APPLICATION_XML)
    public void create(Customer customer) {
        entityManager.persist(customer);
    }

    @GET
    @Produces(MediaType.APPLICATION_XML)
    @Path("{id}")
    public Customer read(@PathParam("id") long id) {
        return entityManager.find(Customer.class, id);
    }

    @PUT
    @Consumes(MediaType.APPLICATION_XML)
    public void update(Customer customer) {
        entityManager.merge(customer);
    }

    @DELETE
    @Path("{id}")
    public void delete(@PathParam("id") long id) {
        Customer customer = read(id);
        if(null != customer) {
            entityManager.remove(customer);
        }
    }

    @GET
    @Produces(MediaType.APPLICATION_XML)
    @Path("findCustomersByCity/{city}")
    public List<Customer> findCustomersByCity(@PathParam("city") String city) {
        Query query = entityManager.createNamedQuery("findCustomersByCity");
        query.setParameter("city", city);
        return query.getResultList();
    }

}

For More Information:

• http://blog.bdoughan.com/2010/08/creating-restful-web-service-part-45.html