Warm up

This lesson is to get you started and give you an idea about JAX-RS in general. Feel free to skip this if you're not new to the framework.

What exactly is JAX-RS ?

JAX-RS is a POJO based, annotation driven framework for building web services which comply with RESTful principles. Imagine writing all the low level code to parse a HTTP request and the logic just to wire these requests to appropriate Java classes/methods. The beauty of the JAX-RS API is that it insulates the developer from the complexity and allows them to concentrate on business logic - that's precisely where the use of POJOs and annotations come into play! It has annotations to bind specific URI patterns and HTTP operations to individual methods of your Java class.

Other notable points

• More on POJO and Annotation driven approach - POJOs can be modelled as Resources with core business logic (in methods) and can be easily wired up with the HTTP request URI (/books?isbn=1234567) and HTTP verb (GET)

• Both for server and client side - The latest version of the API i.e. JAX-RS 2.0 (JSR ???) provides a client side API as well

• Standards driven - The beauty of a standards based API like JAX-RS lies in portability and vendor neutrality. One can easily switch from one implementation to another.

History

Here is a historical snapshot

Release version	Year	Java EE version	MR
JAX-RS 1.0	Oct 2008	Java EE 6	Nov 2009
JAX-RS 2.0	May 2013	Java EE 7	Sep 2014
JAX-RS 2.1	TBD	Java EE 8	TBD

• JAX-RS 2.1 is work in progress

• MR stands for Maintenance Release

Implementations

Here is a list of implementations of the JAX-RS standard

Name	Website	Latest Release (at time of writing)	Packaged with Java EE server
Jersey	jersey.java.net	2.2.22	Glassfish, Weblogic
RESTEasy	http://resteasy.jboss.org/	3.0.12	Wildfly, JBoss
Apache CXF	https://cxf.apache.org/	3.1.6	Apache TomEE

• Jersey serves as the Reference Implementation

• In addition to JAX-RS specification compliance, each implementation also adds it's own proprietary features

Basic tenets of RESTful services

This is the only section which talks about REST in a conceptual manner. Throughout the rest of the book, you'll not see references to abstract concepts

REST stands for Representational State Transfer. Let's quickly zip through some of the important good-to-know-terminologies associated with REST

• Resources - They are the cornerstone of REST based services. Server and client exchange representations of the resource. REST is not about making RPC based calls by simply using XML/JSON payloads (of course no one cab prevent you from doing so - but that cannot be called RESTful)

• Addressable - The resource(s) should be reachable via a URI e.g. https://api.github.com/search/repositories

• HTTP based - One must be able to interact with resources (CRUD) using standard HTTP (GET,PUT,POST, DELETE etc) e.g. Issue a HTTP GET to the URI https://api.github.com/search/repositories?q=user:abhirockzz

• Stateless - HTTP (which is the cornerstone of REST) is inherently stateless protocol and each RESTful payload should contain the related state. There is no co-relation b/w two subsequent requests even if they are the same. Also, a RESTful API should not depend on previous state related data to be sent by the client

• Interaction via Hyperlinks - Let hyperlinks drive the application. Client friendly practice popularly known as HATEOAS (Hypermedia As The Engine Of Application State)

What's important to know is that the JAX-RS framework embraces these principles and helps you create RESTful services and APIs