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Implementing the JAX-RS service of the adapter

To implement the JAX-RS service of the adapter, we must first implement the JAX-RS application class, then implement the JAX-RS resources classes.

Parent topic: Developing Java adapter code

Implementing the JAX-RS application class


The JAX-RS application class tells the JAX-RS framework which resources are included in the application. Any resource can have a separate set of URLs. Traditionally the application class should extend and implement the method getClasses or getSingletons that will be called by the JAX-RS framework to get information about this application.

In the following example, a JAX-RS application defines three resources: Resource1, UsersResource, and MyResourceSingleton. The first two are provided by the getClasses method, while the last is provided by getSingletons.

import java.util.HashSet; import java.util.Set; import; public class MyApplication extends Application{ @Override public Set<Class<?>> getClasses() { HashSet<Class<?>> classes = new HashSet<Class<?>>(); classes.add(Resource1.class); classes.add(UsersResource.class); return classes; } @Override public Set<Object> getSingletons() { Set<Object> singletons = new HashSet<Object>(); singletons.add(MyResourceSingleton.getInstance()); return singletons; } }

Note: The example demonstrates how to write a pure JAX-RS application using getClasses and getSingletons. A quicker alternative is to use extends MFPJAXRSApplication. The MFPJAXRSApplication class scans the package for JAX-RS 2.0 resources and automatically creates a list. Additionally, its init method is called by MobileFirst Server as soon as the adapter is deployed, before it starts serving, and when the MobileFirst runtime starts up.

Implementing a JAX-RS resource


A JAX-RS resource is a POJO (plain old Java object) which is mapped to a root URL and has Java methods for serving requests to this root URL and its sub-URLs. For example:

import java.util.ArrayList; import; import; import; import; import; import; import; import; import; import; import; @Path("/users") //This is the root URL of the resource ("/users") public class UsersResource { //Instead of this static field, it could be a users DAO that works with Database or cloud storage static ArrayList<User> users = new ArrayList<User>(); @GET @Produces(MediaType.APPLICATION_JSON) //This will serve: GET /users public ArrayList<User> getUsers(){ return users; } @Path("/{userId}") @Produces(MediaType.APPLICATION_JSON) //This will serve: GET /users/{userId} public User getUser(@PathParam("userId") String userId){ return findUserById(userId); } @POST @Consumes(MediaType.APPLICATION_JSON) //This will serve: POST /users public void addUser(User u) { users.add(u); } @PUT @Consumes(MediaType.APPLICATION_JSON) //This will serve: PUT /users public Response updateUser(User u) { User user = findUserById(u.getId()); if (user == null){ return Response.status(Status.NOT_FOUND) .entity("User with ID: "+u.getId()+" not found") .build(); } users.remove(user); users.add(u); return Response.ok().build(); } @DELETE @Path("/{userId}") //This will serve: DELETE /users/{userId} public void deleteUser(@PathParam("userId") String userId){ User user = findUserById(userId); users.remove(user); } private User findUserById(String userId) { //TODO implement... return null; } } The resource just shown is mapped to the URL /users and serves the following requests:

Table 1. Resource requests
Request Description
GET /users Gets all users list
POST /user Adds a new user
GET /users/{userId} Gets a specific user with id userId
PUT /users Updates an existing user
DELETE /users/{userId} Deletes a user with id userId

The JAX-RS framework does the mapping from the simple Java object User to a JSON object and conversely, thereby making it easier for the service developer to use without taking care of repeating conversion-related code. The implementation also helps in extracting parameter values from the URL and from the query string without having to parse it manually.

Configuring protection of JAX-RS resources


A JAX-RS adapter resource is protected by default by the MobileFirst security framework, meaning that access to the resource requires a valid access token. See OAuth resource protection. We can configure the resource protection by using the @OAuthSecurity annotation to assign a custom security scope, or to disable resource protection. For a complete reference, see Interface OAuthSecurity. For detailed configuration instructions, see Configure protection of Java API for RESTful Web Services (JAX-RS) resources.