REST introduction

Topics 

• What is and Why REST? 
• Principles of RESTful architecture 
• REST is everywhere 
• REST vs SOAP 
• JAX-RS 
• Tools 
• SpringMVC REST APIs vs Spring REST/JAX-RS APIs

What is and Why REST?

The World Before REST 

• Many different communication standards 
  • RMI, SOAP, CORBA, DCOM, etc. 
• From many different parties 
  • Sun, Microsoft, IBM, etc 
• Caused many problems 
  • Bad interoperability
  • Hard to implement 
  • Vendor 'lock-in'

What is and Why REST?

• REpresentational State Transfer 
  • Introduced by Roy Fielding's in his doctoral thesis “Architectural Styles and the Design of Network-based Software Architecture” 
• He tried to address the following questions 
  • Why is the Web so prevalent and ubiquitous? 
  • What makes Web scale? 
  • How can I apply the architecture of the Web to the “applications”? 
• He found the same set of architectural styles that make Web so successful can be applied to the development/deployment/usage of “applications” and he calls it REST

Benefits of REST: Deployment standpoint

• Scalable 
• High performance 
• Loosely coupled 
• Fault-tolerant 
• Secure 
• Interoperable

Benefits of REST: Development standpoint

• Simple, intuitive, consistent 
• Friendly to developer 
• Programming language independent 
• Most languages have REST support 
• Explorable via HTTP too

REST Architectural Principles

• Addressability 
• Uniform interface 
• Representation-oriented 
• Stateless 
• HATEOAS (Hypermedia As The Engine Of Application State) 
• Cacheable

Addressability

• Every resource has a unique address in the form of a URI 
• URI structure 
  • http://host:port/path?query1=value1&query2=value2#fragment 
  • https://host:port/path?query1=value1&qiery2=value2#fragment 
• Characters allowed 
  • a-z, A-Z, 0-9, ., -, *, _ 
  • Other characters get encoded (space to +, others to %xx) 
• Each resource having a unique URI enables “resources linking” (HATEOAS) 
  • These links can be embedded into the document 
  • The links embedded in the document carry states

Uniform Interface

• HTTP has a fixed set of methods, each of which has specific purpose and pre-defined behavior 
  • GET, PUT, DELETE, POST, HEAD, PATCH, OPTIONS 
• Safety and Idempotency 
  • Safe methods are HTTP methods that do not modify resources 
  • An idempotent HTTP method is a HTTP method that can be called many times without different outcomes

Benefits of Uniform Interface

• Simplicity 
  • There is no need for IDL-like contract (IDL in CORBA, WSDL in SOAP) that specifies what methods are available 
• Easy accessibility 
  • The client does not need any special library or stub (like in the case of SOAP) in order to access the service: all they need is HTTP client library 
• Interoperability 
  • Due to simple requirements, REST clients and REST services are highly interoperable (since there are a lot less moving parts) 
• Scalability 
  • You can take advantage of built-in caching capability of HTTP

CRUD Operations are Performed through HTTP method + URI

Representation-oriented

• Each service (or resource) is addressable through a specific URI and representations are exchanged between client and server 
• With GET, you get current representation of the resource 
• With PUT or POST, you pass a representation of a resource to the server so that the underlying resource state can change 
• The representation has self-descriptive messages

Stateless Communication

• What does “stateless” mean? 
  • It does NOT mean your RESTful application can't have a state – it simply means the server does not maintain client session data 
  • If client session data needs to be maintained, it should be maintained by the client and transferred to the server with each request as needed 
• Benefits of stateless communication 
  • Scalability (because server does not maintain the client session) 
  • Reliability (because there is no lost client session data in case of server crash)

HATEOAS

• Hypermedia As The Engine of Application State (HATEOAS) 
• It enables document centric approach with embedding links (for other resources) within that document 
  • In the same way the web pages we, humans, visited contains links 
• Each document that is returned guides the client to the other resources 
  • In the same way the web pages we, humans, visited gave us the links to click through

Cacheable

• Response messages from the service to its consumers are explicitly labeled as cacheable or non-cacheable 
• The service, the consumer, or one of the intermediary middleware components can cache the response for reuse in later requests

REST is Everywhere

Pretty much all services on the internet are exposed as RESTful services 

• Amazon 
• Google 
• Facebook 
• Tweeter 
• LinkedIn

programmableweb.com

Maintains all REST APIs on the net

Lab: Exercise 2: Explore REST APIs 4361_javarest_introduction.zip

REST vs. SOAP

• SOAP-based web service 
  • Few URIs (nouns), many custom methods (verbs) 
    • musicPort.getRecordings(“beatles”) 
  • Uses HTTP as transport for SOAP messages 
• RESTful web service 
  • Many resources (nouns), few fixed methods(verbs) 
    • GET /music/artists/beatles/recordings 
  • HTTP is the protocol

SOAP Service and REST Resource

• SOAP based web services is about services 
  • Stock quote service
• quoteService.purchase(“goog”, 2000); 
• REST is Resource-Oriented Architecture 
  • Stock quote resource 
  • Resources are manipulated by exchanging representations 
  • Eg. purchasing stock 
    • Manipulate my portfolio resource 
    • Handle a POST in a stock resource that I own 
    • POST /mystocks/goog

Advantages of SOAP over REST

• Transport independence 
  • You can use SOAP over any kind of transport (HTTP/S, JMS, SMTP) while REST works only over HTTP/S 
• Well-defined standards 
  • SOAP has well-defined standards in the area of security, transaction, reliability while REST lacks the standards in these areas 
  • SOAP better suits with stateful operations 
• Well-defined service contact via WSDL 
  • REST now has WADL

Advantages of REST over SOAP

• Simplicity 
• REST works with different representations (XML, JSON, XHTML, etc) while SOAP works only with XML (unless you use different encoding style)

JAX-RS (Java Specification for REST)

Problem in Using Servlet API For Exposing a Resource (Too much coding)

Design Goals of JAX-RS: Java API for RESTful Web Services

• Support REST concepts 
  • Everything is a resource 
  • Every resource is address'able via URI
  • HTTP methods provides uniform interface 
  • Representations (formats) 
  • HATEOAS 
• Support High level and Declarative programming model
  • Use @ annotation in POJOs 
• Generate or hide the boilerplate code 
  • No need to write boilerplate code for every app

Implementations of JAX-RS (JSR 311)

• Jersey – reference implementation of JAX-RS 
  • Download it from http://jersey.dev.java.net 
  • Comes with Glassfish, other Java EE 6+ servers 
• Other open source implementations of JAX-RS 
  • Apache CXF 
  • JBoss RESTEasy
  • Restlet

Development Tools

• IDE – for general purpose RESTful Web service development 
  • Eclipse, Intellij IDEA, NetBeans 
• Client tools – for sending HTTP requests 
  • “Postman” Chrome Application 
  • RESTClient 
  • Several command line tools
    •  curl http://curl.haxx.se/ 
  • soapUI 
• Browser

Lab: Exercise 1: Tools 4361_javarest_introduction.zip

SpringMVC REST APIs vs Spring REST/JAX-RS APIs

Comparison

• JAX-RS is designed with REST in mind 
  • SpringMVC REST is an extension to MVC with REST features 
• JAX-RS is more feature rich than SpringMVC REST 
  • More APIs are available 
• JAX-RS more portable than SpringMVC REST 
  • It is Java standard

You can build Spring REST application using either SpringMVC REST APIs or JAX-RS APIs

How to use JAX-RS APIs in Spring

Add the following dependency
<dependency>
 <groupId>org.springframework.boot</groupId>
 <artifactId>spring-boot-starter-jersey</artifactId>
</dependency>
• Add JerseyConfig.java
@Component
@ApplicationPath("/resources")
public class JerseyConfig extends ResourceConfig {
 public JerseyConfig() {
 register(CustomersResource.class);
 register(OrdersResource.class);
 }
}

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