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Introduction to Web Services

1. Introduction

2. Web Services Architectures3. Implementing Web Services

4. The Java Web Services Developer Pack

-JWSDP

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1. Introduction

Traditional Web Applications-Traditional web-enabled applications are primarily focused on

presentation and are unable to interact with other applications.

stock.com

Stock

broker

weather.com

Weather

reportsnews.com

Headline

News

-The main reason is that they are built using different web technologies,

and their access is limited through an Internet browser or by using an

application-specific client.

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Web Services Paradigm

-Web services introduce a new paradigm for enabling the exchange ofinformation across the Internet using a wide range of computing

platforms, based on the use of open Internet standards and technologies.

-Web services are self-describing and modular business applicationsthat expose the business logic as services over the Internet through

programmable interfaces and using standard internet protocols.

-As such they can be defined as loosely coupled software componentsdelivered over Internet standard technologies.

-Based onXML standards, web services can achieve interoperability of

applications based on different programming languages and platforms.

-This facilitates the delivery of business applications as a service

accessible to anyone, anytime, at any location, and using any platform.

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Travel

services

registry

Travel

reservation

Serviceprovider

automobile

desktop

organization

Airline reservation

system

Credit card

Payment system

Hotel reservation

system

Rental car reservation

systemServicerequestor

Register

services

Find services

Invoke

services

PDA

Example Scenario of Web Services

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2. Web Services Architecture

Basic Operational Model of Web Services

Service

broker

Service

provider

Service

requestor

Invoke service

Register serviceDiscover service

-Web services operations involve three distinct roles and relationships:Service provider: develop, deploy, and publish the web services.

Service broker: responsible for service registration and discovery.

Service requestor: locate, invoke, and execute the web services.

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-A typical web service architectural model consists of three logical

components as core building blocks:services container, services

registry, and services delivery.

-The logical components are implemented using de facto web services

standards: WSDL, UDDI, and SOAP technologies.

Web service Requester

Service

delivery

Web service provider

Services

container

Web service broker

UDDI

registry

ebXML

Registry/

repository

Discover services

& location ofWSDL

Invoke services using

SOAP/ebXML Messaging

Register services

using WSDL

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Simple Object Access Protocol (SOAP)

-XML-based Messaging protocol for exchanging information betweenthe service provider and service requester.

-It consists of the following:

SOAP Envelope: describes the message contents and processing info.SOAP Transport: defines the binding for the underlying transport

protocol such as HTTP and SMTP.

SOAP Encoding: defines a set of encoding rules for mapping the

instances of the application-specific data types to XML elements.SOAP RPC conventions: defines the representation of the RPC

requests and responses.

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Web Services Description Language (WSDL)

-XML schema-based specification for describing Web services as acollection of operations and data input/output parameters as messages.

-Defines the communication model with a binding mechanism to attach

any transport protocol, data format, or structure to an abstract message

or operation.

Universal Description, Discovery, and Integration (UDDI)-Defines a mechanism to register and categorize Web services in a

registry that users communicate to in order to discover and locate

registered services.

-A query submitted to the UDDI returns the WSDL description of the

service interface. The developer can use this description to construct a

SOAP client interface that can communicate with the service provider.

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ebXML

-Provide a standard framework for building an e-business by enablingthe standardization of business processes and profiles, and partner

agreements.

-Complement other Web services standards such as SOAP, WSDL, andUDDI, in order to provide a reliable framework for e-business tasks.

-Major features include the following:

ebXML Messaging service (MS): SOAP plus reliability and security.

ebXML CPP/CPA: WSDL augmented to enable business partner

profiles and agreements to be described.

ebXML reg/rep: provides registry and repository (UDDI is just aregistry).

ebXML Core components: provide a catalogue of business process

components for the business community.

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Web Services Communication Models

-Web services can be implemented using eitherRPC-basedsynchronous or messaging-based asynchronous communication

models.

RPC-Based Communication ModelRequest

Response

Web service

requester

Web serviceprovider

-The client invokes the Web services by sending parameter values to

the service provider that executes the required methods, and thensends back the return values.

-When the client sends a request, the client waits until a response is

sent back from the server before continuing any operation.

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Messaging-Based Communication Model

Message

Web servicerequester

Web service

provider

-Loosely coupled communication model which supports asynchronous

messaging.

-The client typically sends an entire document to the service provider.

The service provider receives and processes the document, and then

may or may not return a result.

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3. Implementing Web Services

Web Services requester

Service delivery

-SOAP Clients

Web Services Broker

UDDI basedRegistry Services

Web Services Provider

Service container

-SOAP Interfaces

-WSDL Descriptions

1.Create SOAP proxy interfaces

and WSDL based service

descriptions

2.Register/publishservices

3.Stores service descriptions

as binding templates&URL

4.Locates services

and its binding info

5.Invoke & obtain WSDL

6.Exchange data using

SOAP RPC/Messaging

General Approach

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Developing Web Services-Enabled ApplicationsWeb Services Requestor

Service delivery

-SOAP client

preferences

Invoke

services

SOAP

Web Services Provider

Service runtime environment

-SOAP interface classes

-XML descriptors

-WSDL

J2EE

Microsoft.NET

CORBA

- A Web service can be created as a new application or from using an

existing application by re-purposing them as services.

-In either case, the business components (J2EE, CORBA, .Net) must be

encapsulated as service-oriented interfaces using SOAP and exposed

as web services by deploying them in a web service container.

-The service requestor finds the services through UDDI. To invoke the

services exposed by the provider, the requester is required to implement

SOAP-based client interfaces according to the WSDL description.

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4.The Java Web Services Developer Pack -JWSDP

Overview-The combination of Java and XML provides an excellent solution

for developing interoperable, portable, and extensible applications:

XML is a cross-platform neutral data format and Java is a crossplatform programming language.

-The integration of both technologies requires the development of

parsers and other supporting technologies to process the XML data.The JWSDP proposed by SUN is one such technology.

-The core components of JWSDP include the following:

Java XML packApache Tomcat container

JWSDP Registry server

JavaServer Pages Standard Tag libraries

ANT Build tool

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Java XML Pack

-Consists of a set of high-level APIs and reference implementationsthat abstract the complexities behind XML processing. The following

APIs are available:

Java API for XML Parsing (JAXP)

Java API for XML Registries (JAXR)Java API for XML-based RPC (JAX-RPC)

SOAP with Attachments API for Java (SAAJ)

Java API for XML Messaging (JAXM)

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Java API for XML Processing (JAXP)

-Used for the parsing and transformation of XML documents:Parsing: the process of interpreting the content of a structured XML

document ->SAX, DOM

Transformation: consists of applying a template to the XML data in

order to produce a document in a desired format->XSLT

Simple Access for XML (SAX) API

-Event-driven processing model where data elements are interpreted on

a sequential basis and events are triggered based on selected constructs.

-Since it does not load any XML documents into memory it is very fast

and lightweight.

JAXP

Compliant

Parser

Default

Handler

event

event

event

input

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Document Object Model (DOM) API

-Its processing model consists of reading the entire document intomemory and building a tree representation of the structured data,

which can be used to manipulate the data by inserting, deleting or

editing elements.

JAXP

Compliant

Parser

BuildDOMinput

Document

Extensible Stylesheet Language Transformation (XSLT)-eXstensible Stylesheet Language (XSL) is used to describe templates

for converting XML documents in desired formats (XML, HTML,

PDF, WML etc.).

-XSLT is the processor that performs the formatting task.

JAXP Compliant

XSLT Processor

input

wml

html

pdfXSL

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Java Architecture for XML Binding (JAXB)

-Provides application developers with a way to generate Java objects

based on XML definitions and vice versa, more specifically:Marshalling: converting a Java object tree into an XML document.

Unmarshalling: converting an XML document into a Java object tree.

Validation:checking an XML document for conformance with a DTD.

XML schema

Instance Of

marshalling

unmarshalling

XML

document

Java Object

Java Object

compiling

Conforms to

Java classJava class

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Java API for XML Messaging (JAXM)

-Lightweight XML messaging API for application-to-application (A2A)

integration and business-to-business (B2B) communication.

JAXM API JAXM API

JAXM Messaging

Provider

JAXM Messaging

ProviderSOAP

message HTTPHTTP

Receiver ApplicationSender Application

Java API for XML Remote Procedure Calls (JAX-RPC)-Set of high-level Java APIs enabling XML-based Java applications

to interoperate using RPC.

UDDI

Application server

-JAX-RPC runtime

-JAX-RPC API

-Service endpoint

3. Soap/http request

4. Soap/http response1. Lookup

service

2. Return

information

Client

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ANT Build Tool

-Build tool similar to make and gnumake, that uses XML for specifyingthe various tasks that must be executed in the build process.

-Provides many defined tasks that can be used by the developer while

compiling, building, or deploying the application code.

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Developing RPC Web Services with JAX-RPC-JAX-RPC defines an API framework and runtime environment forcreating and executing XML-based remote procedure calls.

-The Web Service requestors invoke the service providers methodsand transmit parameters and then receive return values as XML-based

requests and responses.

-The JAX-RPC-based Web services can be deployed in java servlet

2.2- or the J2EE 1.3-compliant server providers. JAX-RPC-based

services and clients are developed and deployed as J2EE

components.

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JAX-RPC Application Architecture

-A typical JAX-RPC application architecture model involves:

JAX-RPC Service: Java business component (e.g. servlet, bean).

JAX-RPC Service client: access exposed Web service.

Serialization/Deserialization:Java-to-XML and XML-to-Java mappings

JAX-RPC Runtime Environment: runtime mechanisms and executionenvironment for the Web services and service clients.

J2SE Environment

JAX-RPC Client

Invocation

Stubs/Dynamic Proxy/DLL

JAX-RPC Runtime

JWSDP Environment

JAX-RPC-based Service

TIES

JAX-RPC Runtime

WSDL

Request/Response

Soap over HTTP

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JAX-RPC-based Service Implementation

-JAX-RPC services can be implemented using Java classes ( RMI)

or by using a WSDL document.

Developing a JAX-RPC Service from Java Classes

-The key steps include the following:1. Define the Remote interface (Service Definition).

2. Implement the remote interface (Service Implementation).

3. Configure the Service.

4. Generate the Stubs and ties.

5. Package and deploy the service.

Developing a JAX-RPC-based Service from a WSDL Document

-This consists of developing a JAX-RPC-based service using a WSDL

document exposed by an existing Web services environment.

-The key steps include the following:1. Create a service configuration referring to the WSDL.

2. Generate the client-side stubs and server-side ties.3. Package and deploy the service.

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JAX-RPC Client Implementation

-Can be implemented either as stub-based or dynamic proxy-based or

dynamic invocation interface based.

Stub-based Client

-Uses the local stub classes generated by thexrpcc tool.

Dynamic Proxy-based Client

-Enables the invocation of a target service endpoint dynamically at

runtime, without requiring a local stub class.

Dynamic Invocation Interface (DII) Client

-Enables the client to discover and invoke target services dynamically

at runtime.

-The client uses a set of operations and parameters, and a search

criterion to discover the target service. Hence a client can invoke

a service and its methods without knowing its data types.