JAX-RS on Google App Engine

Last week I’ve been playing around with Google App Engine (GAE). Setting up the SDK with Eclipse and the Google Plugin for Eclipse was a breeze. Creating a simple webapp, testing it locally, and deploying it to appspot was a piece of cake. But then I figured I wanted to add a REST interface to my application…

I did not want to use GAE’s Google Cloud Endpoints – using the @Api annotation – because I didn’t want to tie myself to GAE. I wanted to use the JAX-RS standard so my application is portable across different Java application servers.

So the first option I looked at was Jersey, because I’ve use it before. But because of a incompatibility between asm versions (see stackoverflow for more details) I quickly decided to look for alternative JAX-RS implementations.

Next, I figured I’d give JBoss’ RESTEasy a try. But for some reason I just couldn’t get it to run on GAE. So after 10 minutes or so, I gave up.

So finally I decided to give Restlet a go, mainly because they offer a GAE edition. And within a couple of minutes I had a very basic REST service up and running. Here’s what I did:

1. Fire up Eclipse and create a new Google Web Application project.
2. Go to Restlet and download and unzip the GAE Edition of Restlet.
3. Add the following jar files from the Restlet distribution to the war/WEB-INF/lib folder of the project and to its build path: javax.ws.rs.jar, org.restlet.jar, org.restlet.ext.servlet.jar, org.restlet.ext.jaxrs.jar, and org.json.jar.
4. Add a very basic POJO:
   
   Java

   package it.jdev.appengine; public class Product { String name; int quantity; public String getName() { return name; } public void setName(String name) { this.name = name; } public int getQuantity() { return quantity; } public void setQuantity(int q) { this.quantity = q; } }

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   package it.jdev.appengine;   public class Product {   String name; int quantity;   public String getName() { return name; }   public void setName(String name) { this.name = name; }   public int getQuantity() { return quantity; }   public void setQuantity(int q) { this.quantity = q; }   }

5. Add a simple REST service:
   
   Java

   package it.jdev.appengine; import javax.ws.rs.Consumes; import javax.ws.rs.GET; import javax.ws.rs.POST; import javax.ws.rs.Path; import javax.ws.rs.Produces; import javax.ws.rs.core.Response; @Path("products") public class ProductResource { @GET @Produces("application/json") public Product getProduct() { Product product = new Product(); product.setName("Nexus 7"); product.setQuantity(999); return product; } @POST @Consumes("application/json") public Response createProduct(Product product) { String result = "Product created : " + product; return Response.status(201).entity(result).build(); } }

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   package it.jdev.appengine;   import javax.ws.rs.Consumes; import javax.ws.rs.GET; import javax.ws.rs.POST; import javax.ws.rs.Path; import javax.ws.rs.Produces; import javax.ws.rs.core.Response;   @Path("products") public class ProductResource {   @GET @Produces("application/json") public Product getProduct() { Product product = new Product(); product.setName("Nexus 7"); product.setQuantity(999); return product; }   @POST @Consumes("application/json") public Response createProduct(Product product) { String result = "Product created : " + product; return Response.status(201).entity(result).build(); }   }

6. Create the JAX-RS Application:
   
   Java

   package it.jdev.appengine; import java.util.HashSet; import java.util.Set; import javax.ws.rs.core.Application; public class ExampleApplication extends Application { @Override public Set<class<?>&gt; getClasses() { Set<class<?>&gt; classes = new HashSet<class<?>&gt;(); classes.add(ProductResource.class); return classes; } }</class<?></class<?></class<?>

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   package it.jdev.appengine;   import java.util.HashSet; import java.util.Set;   import javax.ws.rs.core.Application;   public class ExampleApplication extends Application {   @Override public Set<class<?>&gt; getClasses() { Set<class<?>&gt; classes = new HashSet<class<?>&gt;();          classes.add(ProductResource.class);          return classes; }   }</class<?></class<?></class<?>

7. Next, it is necessary to make the JAX-RS application known to Restlet by extending org.restlet.ext.jaxrs.JaxRsApplication
   
   Java

   package it.jdev.appengine; import org.restlet.Context; import org.restlet.ext.jaxrs.JaxRsApplication; public class MyJaxRsApplication extends JaxRsApplication { public MyJaxRsApplication(Context context) { super(context); this.add(new ExampleApplication()); } }

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   package it.jdev.appengine;   import org.restlet.Context; import org.restlet.ext.jaxrs.JaxRsApplication;   public class MyJaxRsApplication extends JaxRsApplication {   public MyJaxRsApplication(Context context) { super(context); this.add(new ExampleApplication()); }   }

8. Finally, configure your application to use Restlet in your web.xml deployment descriptor:
   
   XHTML

   ... <servlet> <servlet-name>RestletServlet</servlet-name> <servlet-class>org.restlet.ext.servlet.ServerServlet</servlet-class> <init-param> <param-name>org.restlet.application</param-name> <param-value>it.jdev.appengine.MyJaxRsApplication</param-value> </init-param> </servlet> <servlet-mapping> <servlet-name>RestletServlet</servlet-name> <url-pattern>/*</url-pattern> </servlet-mapping> ...

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   ...   <servlet> <servlet-name>RestletServlet</servlet-name> <servlet-class>org.restlet.ext.servlet.ServerServlet</servlet-class> <init-param> <param-name>org.restlet.application</param-name> <param-value>it.jdev.appengine.MyJaxRsApplication</param-value> </init-param> </servlet>   <servlet-mapping> <servlet-name>RestletServlet</servlet-name> <url-pattern>/*</url-pattern> </servlet-mapping>   ...

If you now start your application locally by selecting Run As > (Google) Web Application and point your web browser to http://localhost:8888/products you should see the following response:
{“name”:”Nexus 7″,”quantity”:999}