J2EE WebServices

Introduction to Web Services

Why Web Services and advantages over conventional equivalent system ?

Core concepts

J2EE web services – various frameworks/technologies

“ Web services are software components that interact with one another dynamically via standard internet technologies making it possible to build bridges between IT systems that otherwise would require extensive development efforts.”

Easy way to define web services is: It is s/w component which can be exposed as service on web. Can be consumed by any client in a language independent way by the use

of standard xml specification.

INTRODUCTION TO WEBSERVICES

WSDL

Web Service(J2EE, PL/SQL,

.NET,C/C++,Legacy …)

Web Service(J2EE, PL/SQL,

.NET,C/C++,Legacy …)

Web ServiceClient

(J2EE, .NET,PL/SQL …)

Web ServiceClient

(J2EE, .NET,PL/SQL …)

Points to description

DescribesService

FindsService

Invokes withXML Messages

SOAP

UDDI Registry

Points to service

Conventional Approaches of exposing/consuming a service

RMI in JavaWhen we want to expose certain service in Java , we can expose it thru

RMIThe client can later consume that service using RMI protocol.

Problem ?

ConceptsConcepts related to J2EE servlet (how it works) –

In web.xml servlet url mapping and servlet class is configured.Servlet class(basically user defined class) extends HttpServlet and Implement one of the methods doGet/doPost.

About HTTP HTTP packet – has header part & body partHTTP methods – GET/POST/PUT/DELETE/TRACE/OPTIONSGET – generally used for requesting some infoPOST – used for processing part for e.x saving form data in DB.

So, how does the request works??? – a demo

HOW J2EE web services are related with it?

Few terminologies/technology used in web services

XML SOAP – basically a xml based message format(protocol) <soap:Envelope xmlns:soap="http://www.w3.org/2001/12/soap-envelope"

soap:encodingStyle="http://www.w3.org/2001/12/soap-encoding"><soap:Header> ... ... </soap:Header><soap:Body> ... ...

<soap:Fault> ... ... </soap:Fault> </soap:Body>

</soap:Envelope> UDDI- Universal Description Discovery Integration – place where webservices are published WSDL – web services description language, this is what makes web services language independent. Its basically contract what server and client has to follow. JAX-RPC – Java API for XML-based RPC

Supports component-based Web-service development JAXP – Java API for XML Processing

framework for parsing and transforming XML docs JAXB – Java Architecture for XML Binding

Mechanism for creating Java objects corresponding to XML Schema elements and attributes SAAJ – SOAP with Attachments API for JAVA

Simple object model for managing SOAP message content

J2EE web services implementation

JAX- RPC – implementations -> axis (from Apache)

JAX-WS – implementations -> Metro(from Sun), JBOSS JAX-WS, Weblogic JAX-WS, IBM JAX-WS

JWSDP – Java WebServices Developer Pack

Ways of creating webservices

Bottom up approach- creating service endpoint first, then generating WSDL file

Top Down approach – creating wsdl file first, then creating the service class

How does the communication work for J2EE web services

Client follows the contract specified in wsdl file i.e where the service is located and how to invoke the service.

Client invokes the service, the request goes as soap message wired over HTTP and waits for the result. So, which HTTP method?

Server processes the HTTP body which contains soap message which is further de-serialize to invoke the actual class’s method.

Server sends the SOAP response message as HTTP body payload which client receives.

What are these implementation all about?

All are SOAP runtime environment.

All are deployed as servlet i.e the core concept is same

Services are wrapped inside the servlet

Can be used either at server/client side

Processing SOAP message using handlers

When handlers are required ?– can be used for security/logging

Writing handlers – a simple demo

How about security ?

HTTPS

XML Encryption- XML Security Suite from IBM,

Trust Services Integration Kit(TSKIT) from Verisign

Processing SOAP message using handlers

When handlers are required ?– can be used for security/logging

Writing handlers – a simple demo

References

Developing Java Web Services (Wiley Publication)

The Ultimate Guide – J2EE Web Services by Richard Monson-Haefel