What is JAX-RS?

Inclusion in Java EE 

JAX-RS is like a set of interfaces and annotations that Java EE (Enterprise Edition) offers, and indeed we have the implementations; some of the more well-known are RESTEasy and Jersey.

Let us think of a case where you want to build an application server that is JEE-compliant, and then your server has to provide a JAX-RS implementation for the deployed apps to use. That is why it is called a Java Enterprise Edition Platform.

Your Server Recognition

Generally, it is advised that the platform we are using, we should take advantage of the platform that we're offered. At least for Production environments, we should see what JAX-RS implementation (like name, vendor, version, and known bugs) exists in the server before deciding to use it. For example, Wildfly or Jboss comes with RESTEasy, while Glassfish comes with Jersey.

So, at the beginning of the project or when you are migrating to another server, you should, at least once, have a piece of knowledge about all the points discussed above.

An Example

Let us see an instance where we are using JAX-RS. There are certain ways, but the shortest path is: to have a Maven web app project with the following dependency in the pom.xml:

<dependency>
    <groupId>javax</groupId>
    <artifactId>javaee-api</artifactId>
    <version>7.0</version>
    <scope>provided</scope>
</dependency>

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We have used JavaEE 7 because there are already plenty of application servers implementing it. Most of the annotations that you need to use are present in the API jar, which is located in package javax.ws.rs. The scope is "provided" because this jar is required at compile time and doesn't need to be in the final build. The server provides it for the run time.

After successfully adding the dependency, the entry class is first written: an empty class that extends javax.ws.rs.core. Application and is annotated with javax.ws.rs.ApplicationPath:

@ApplicationPath("/api")
public class RestApplication extends Application {
}

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We have declared the entry path as being /api. The other ways we declare for our resources, will be prefixed with /api.

Next, let's see a resource:

@Path("/notifications")
public class NotificationsResource {
    @GET
    @Path("/ping")
    public Response ping() {
        return Response.ok().entity("Service online").build();
    }
 
    @GET
    @Path("/get/{id}")
    @Produces(MediaType.APPLICATION_JSON)
    public Response getNotification(@PathParam("id") int id) {
        return Response.ok()
          .entity(new Notification(id, "jack", "test notification"))
          .build();
    }
 
    @POST
    @Path("/post/")
    @Consumes(MediaType.APPLICATION_JSON)
    @Produces(MediaType.APPLICATION_JSON)
    public Response postNotification(Notification notification) {
        return Response.status(201).entity(notification).build();
    }
}

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File Download Example: RESTful JAX-RS 

JAX-RS API in Java can be used to download various types of files like text, images, pdf, etc. Just a few lines of code can do this.

You need to specify the different content types to download additional files. The @Produces annotation is used to identify the type of file content.

1. @Produces("text/plain"): for downloading text file.
2. @Produces("image/png"): for downloading png image file.jo
3. @Produces("application/pdf"): for downloading PDF file.
4. @Produces("application/vnd.ms-excel"): for downloading excel file.
5. @Produces("application/msword"): for downloading ms word file.

RESTful JAX-RS File Upload Example

We saw in the previous topic that we can download files; likewise, we can easily upload a file. The @FormDataParam("file") annotation mentions the file parameter in the service class. The @Consumes(MediaType.MULTIPART_FORM_DATA) provides information about the file upload.

Frequently Asked Questions

What is a RESTful API?

A RESTful API can be defined as an architectural style that is primarily used for an application program interface (API). HTTP requests are used to access and, use data. That data can be used to GET, PUT, POST and, DELETE data types, which refers to the reading, updating, creating and deleting of operations concerning resources.

What is a web service?

A Web Service is defined as a client-server application. It is the method of communication between two devices over the network and a collection of standards for exchanging information between two devices or application.

What are the advantages of RESTful web services?

RESTful web services are fast, language and platform dependent and permit different data formats.

Conclusion

So, we can conclude that JAX-RS is a powerful API, and your web server may already implement many of the things you may need. This makes it easy as you no more need to turn your deployable code into an unmanageable pile of libraries.

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