RESTful Java with JAX-RS by Bill Burke

Author:Bill Burke [Bill Burke]
Language: eng
Format: epub, mobi
Tags: COMPUTERS / Programming Languages / Java
ISBN: 9781449377519
Publisher: O'Reilly Media
Published: 2009-11-09T16:00:00+00:00

The Application Class

Before looking at what we have to do to configure a web.xml file, we need to learn about the javax.ws.rs.core.Application class. Although Java EE 6 has additional discovery options, the Application class is the only portable way of telling JAX-RS which web services (@Path annotated classes) as well as which MessageBodyReaders, MessageBodyWriters, and ContextResolvers (@Provider annotated classes) you want deployed. I first introduced you to the Application class back in Chapter 3:

package javax.ws.rs.core; import java.util.Collections; import java.util.Set; public abstract class Application { private static final Set<Object> emptySet = Collections.emptySet(); public abstract Set<Class<?>> getClasses(); public Set<Object> getSingletons() { return emptySet; } }

The Application class is very simple. All it does is list classes and objects that JAX-RS is supposed to deploy. The getClasses() method returns a list of JAX-RS web service and @Provider-annotated classes. JAX-RS web service classes follow the per-request model mentioned Chapter 3. @Provider classes are instantiated by the JAX-RS container and registered once per application.

The getSingletons() method returns a list of preallocated JAX-RS web services and @Provider-annotated classes. You, as the application programmer, are responsible for creating these objects. The JAX-RS runtime will iterate through the list of objects and register them internally. When these objects are registered, JAX-RS will also inject values for @Context annotated fields and setter methods.

Let’s look at a simple example of an Application class:

import javax.ws.rs.core.Application; public class ShoppingApplication extends Application { public ShoppingApplication() {} public Set<Class<?>> getClasses() { HashSet<Class<?>> set = new HashSet<Class<?>>(); set.add(CustomerResource.class); set.add(OrderResource.class); set.add(ProduceResource.class); return set; } public Set<Object> getSingletons() { JsonWriter json = new JsonWriter(); CreditCardResource service = new CreditCardResource(); HashSet<Object> set = new HashSet(); set.add(json); set.add(service); return set; } }

Here, we have a class ShoppingApplication that extends the Application class. The getClasses() method allocates a HashSet and populates it with @Path annotated classes and returns the set. The getSingletons() method allocates a MessageBodyWriter class named JsonWriter and an @Path annotated class CreditCardResource. It then creates a HashSet and adds these instances to it. This set is returned by the method.

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