RESTful Web Services in JEE, JDBC, J2EE, JAVA Software

RESTful Web Services in JEE By Omprakash Pandey

What is REST?

What is REST
Representational State Transfer
Architectural Style to leverage modern Web (HTTP and XML) and a Design Pattern
Wide spread vendor and open source support
Used by Developer, Architect, Manager and Executives
Emphasizes on Scalability of Component interactions

REST defined
Resources are identified by uniform resource identifiers (URIs)
Resources are manipulated through their representations
Messages are self-descriptive and stateless
Multiple representations are accepted or sent
Hypertext is the engine of application state

Credits
The guts of this presentation comes from the writings of:
Roy Fielding
Ryan Tomayko
Paul Prescod
Mark Baker
Jeff Bone (conversus)
All the contributors to RestWiki

REST style
Client-server
Stateless
Cached
Uniform interface
Layered system
(Code on demand)

REST Features
Generality of interfaces
Independent deployment of components
Intermediary components to reduce interaction latency
Enforce Security
Encapsulate legacy systems
Clean separation of client interface from server implementation
Statelessness
Cache ability

REST Features
REST requires the use of a common, generalized, generic interface.
Does not permit application-specific interfaces.
In the Web world, the REST interface is defined by the HTTP interface, which supports four basic application methods: GET, POST, PUT, and DELETE.“
Provides full control over development
REST has Noun orientation and works around Data – centric model

REST Features
REST is a lightweight alternative to mechanisms like RPC (Remote Procedure Calls) and Web Services (SOAP, WSDL, etc.)
REST is not a standard
REST service is:
Language-independent
Standards-based (runs on top of HTTP)
Can easily be used in the presence of firewalls

Restful Web Service Principles
Resources and representations
Addressability and connectedness
Uniform interface
Statelessness

SQL and HTTP Verbs Action SQL HTTP Create Insert PUT Read Select GET Update Update POST Delete Delete DELETE

RESTful Applications
RESTful applications use
HTTP requests to post data (create and/or update),
read data (e.g., make queries),
and delete data.
REST uses HTTP for all four CRUD (Create/Read/Update/Delete) operations.
Offers no built-in security features, encryption, session management, QoS guarantees, etc.
.

Web Service Issues
Complex Web Service Specifications and Standards
Web services development is unnecessarily complex, slow and laborious
Based on SOAP message format
Based on WSDL schema and proxy generation
XML-RPC is based on verb orientation as command to a service

SOAP vs REST
<?xml version="1.0"?> <soap:Envelope xmlns:soap="http://www.w3.org/2001/12/soap-envelope" soap:encodingStyle="http://www.w3.org/2001/12/soap-encoding"> <soap:body pb="http://www.acme.com/phonebook"> <pb:GetUserDetails> <pb:UserID>12345</pb:UserID> </pb:GetUserDetails> </soap:Body> </soap:Envelope>
SOAP is similar to a mailing letter with envelope
http://www.acme.com/phonebook/UserDetails/12345
REST can easily handle more complex requests, including multiple parameters
REST is similar to a postcard

REST Response Format
Server response in REST is often an XML file
REST can use CSV or JSON format
HTML is in fact the most common REST response format

Real REST Examples
The famous Twitter API is all REST.
Yahoo! offer most of their services using REST. This includes
Search API, Maps, Photos, Traffic
Flickr ,
Amazon.com offer several REST services, e.g., for their S3 storage solution
Atom is a RESTful alternative to RSS.

This ain't the REST Design Pattern Premier Members Frequent Flyer Members Regular Members Reservation Web Service Determine Priority Premier Customer F.F. Customer Regular Customer client client client

This is the REST Design Pattern Premier Members Frequent Flyer Members Regular Members client client client http://www.kings-air/reservations/premier http://www.kings-air/reservations/frequent-flyer http://www.kings-air/reservations/regular Premier Member Reservation Service Frequent Flyer Reservation Service Regular Member Reservation Service

REST Architecture Components
Resources – identified by logical URLs
Resources are the key element of a true RESTful design
Appropriately linked resources
Client Server
Stateless
Cacheable
Proxy Server

AJAX and REST
AJAX, requests are sent to the server using XMLHttpRequest objects
Each XMLHttpRequest can be viewed as a REST service request, sent using GET.
The response is often in JSON, a popular response format for REST

REST Design Guidelines
Do not use physical url, Use Logical URL
http://www.abc.com/inventory/product/003
Queries should not return an overload of data
Provide Paging instead
REST response should be well documented
Include the actual URLs with REST responses
http://www.acme.com/product/001263
GET access requests should never cause a state change. State Change should be a POST request.
Use Web Application Description Language (WADL )

When to use REST
Check if interaction can survive server restart
A caching infrastructure can be leveraged for performance
The service producer and service consumer have a mutual understanding of the context and content being passed along
REST is particularly useful for limited-profile devices such as PDAs and mobile phones
Web service delivery or aggregation into existing web sites can be enabled easily with a RESTful style

REST in Java
The key class here is HttpURLConnection , obtained by invoking openConnection on a URL object
public static String httpGet(String urlStr) throws IOException {
URL url = new URL(urlStr);
HttpURLConnection conn = (HttpURLConnection) url.openConnection();
if (conn.getResponseCode() != 200) {
throw new IOException
(conn.getResponseMessage()); }
BufferedReader rd = new BufferedReader( new InputStreamReader(conn.getInputStream()));
StringBuilder sb = new StringBuilder();
String line;
while ((line = rd.readLine()) != null) {
sb.append(line); }
rd.close();
conn.disconnect();
return sb.toString();
}

public static String httpPost(String urlStr, String[] paramName, String[] paramVal) throws Exception {
URL url = new URL(urlStr);
HttpURLConnection conn = (HttpURLConnection) url.openConnection(); conn.setRequestMethod("POST");
conn.setDoOutput(true);
conn.setDoInput(true);
conn.setUseCaches(false);
conn.setAllowUserInteraction(false);
conn.setRequestProperty("Content-Type", "application/x-www-form-urlencoded"); // Create the form content
OutputStream out = conn.getOutputStream();
Writer writer = new OutputStreamWriter(out, "UTF-8");
for (int i = 0; i < paramName.length; i++) {
writer.write(paramName[i]);
writer.write("=");
writer.write(URLEncoder.encode(paramVal[i], "UTF-8")); writer.write("&");
}
writer.close();
out.close();
if (conn.getResponseCode() != 200) {
throw new IOException(conn.getResponseMessage()); }
BufferedReader rd = new BufferedReader( new InputStreamReader(conn.getInputStream()));
StringBuilder sb = new StringBuilder(); String line;
while ((line = rd.readLine()) != null) {
sb.append(line); }
rd.close();
conn.disconnect();
return sb.toString(); }

JAX-RS
HTTP-based architectural style is named Jersey, or JSR-311
ServletAdapto r class in the com.sun.ws.rest.impl.container.servlet package
javax.ws.rs
javax.ws.rs.core
javax.ws.rs.ext

Advantages of REST
Its architectural constraints when applied as a whole , generate:
Scalable component interactions
General interfaces
Independently deployed connectors
Reduced interaction latency
Strengthened security
Safe encapsulation of legacy systems

Advantages of REST
Supports intermediaries (proxies and gateways) as data transformation and caching components
Concentrates the application state within the user agent components, where the surplus disk and cycles are

Advantages of REST
Separates server implementation from the client's perception of resources (“Cool URIs Don’t Change”)
Scales well to large numbers of clients
Enables transfer of data in streams of unlimited size and type

WADL elements
Application
Grammar
Include
Resources
Resource
Resource Type
Method
Request
Response
Representation
Param
Link
Doc
https://wadl.dev.java.net/wadl20090202.pdf

Resource Oriented Architecture
Addressability
Statelessness
Connectedness
Representations
Xml; html; xhtml; json; pdf…
Uniform Interface

RESTful Web Services in JEE, JDBC, J2EE, JAVA Software

by Synergetics India on Aug 05, 2010

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RESTful Web Services in JEE, JDBC, J2EE, JAVA Software Presentation Transcript