Enterprise Computing:Web Services

Exercise

What is wrong with JEE?

Why would you not use it for web-based application integration?

Why would you not use it for intranet-based application integration?

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Web Services: Definitions

A Web service is a collection of functions that are packaged as a single entity and published to the network for use by other programs.

Web services are building blocks for creating open distributed systems, and allow companies and individuals to quickly and cheaply make their digital assets available worldwide.

Web Service standards form a platform-independent, open framework for describing services, discovering businesses, and integrating business services.

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eXtensible Markup Language

A common data format derived from SGML Language independent, hierarchical and self-describing Uses tag-based structure similar to HTML to define XML

documents<?xml version="1.0" encoding="ISO-8859-1" ?> <bankaccount type=“Current”>  <name>John Smith</name>   <address>

<line 1>1 Grafton Street </line1><line 2>Dublin 2, Ireland </line2></address>

</bankaccount>

Supports arbitrarily complex data formats Schema (defined in xsd files) can be used to define document

formats Fragment defining a BankAccount as a type of financial record

<xsd:element name="purchaseOrder" type="PurchaseOrderType"/>

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eXtensible Markup Language

Independent of IT infrastructure Separates the what from the how

Many industry based schema standards have been developed For example, Financial Services:

ISO15022 (SWIFT, FIX, FpML) XBRL (business reporting)

Any XML based infrastructure can handle multiple and evolving schema standards without excessive cost Due to changes in business relationships Due to regulatory changes (e.g. Basil II) Due to evolution of the schemas themselves

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The Web Services architecture

UDDIRegistry

2. Request contract information

3. Retrieve WSDL definition

4. Exchange SOAP messages

WSDL

1. Register contract information

ServiceConsumer

ServiceProvider

WSDL

Web Services is based on three standards

Simple Object Access Protocol (SOAP) defines the communication mechanism

Universal Directory Discovery Interface (UDDI) defines the registry of interface definitions

Web Service Definition Language defines the actual interfaces

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SOAP- Simple Object Access Protocol

XML based protocol for exchange of information Encoding rules for datatype

instances Convention for representing

RPC invocations

Used with XML Schema Normally HTTP-based

Uses Request/Response Two different modes

RPC Document

SOAP with Attachments allow arbitrary data to be packaged.

SOAP1.1 MessageStructure

SOAPEnvelope

HeaderEntries

Header

Body

FaultElement

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SOAP Example: Request

Sample SOAP Message embedded in an HTTP Request

POST /StockQuote HTTP/1.1Host: www.stockquoteserver.comContent-Type: text/xml; charset="utf-8"Content-Length: 1024SOAPAction: "http://example.org/2001/06/quotes"

<env:Envelope xmlns:env="http://www.w3.org/2001/06/soap-envelope" ><env:Body><m:GetLastTradePrice env:encodingStyle="http://www.w3.org/2001/06/soap-encoding" xmlns:m="http://example.org/2001/06/quotes"><symbol>IBM</symbol></m:GetLastTradePrice></env:Body></env:Envelope>

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SOAP Example: Response

SOAP message sent by the StockQuote service in the corresponding HTTP response to the request

HTTP/1.1 200 OKContent-Type: text/xml; charset="utf-8"Content-Length: 512

<env:Envelope xmlns:env="http://www.w3.org/2001/06/soap-envelope" ><env:Body><m:GetLastTradePriceResponse env:encodingStyle="http://www.w3.org/2001/06/soap-encoding" xmlns:m="http://example.org/2001/06/quotes"><Price>97.5</Price></m:GetLastTradePriceResponse></env:Body></env:Envelope>

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UDDI• Universal Description, Discovery and Integration

• Platform-independent, open framework for describing services, discovering businesses, and integrating business services.

• A DNS-like model implementation of the directory

• Originally intended to support global registries

• Created during the .com bubble.

• Includes White, Green and Yellow Pages for search purposes

• Now primarily inside organisations if at all

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Web Service Description Language (WSDL)

Interface definition language in XML Conceptually, no different from Enterprise Java Bean or

Common Gateway Interface Based on XML Schema Can appear to be very verbose

An interface description is a contract between the server developers and the client developers WSDL describes the web service Similar to Java method signatures

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Interoperability Challenges

Interoperability remains the chief challenge of web services Complex and imprecise standard Tools generating SOAP, WSDL, UDDI, etc. need to be

interoperable

Web Services Interoperability (WS-I) focus on creating to Interoperability WS-I Basic Profile 1.0 defines an interoperable web services

platform

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WS-I Basic Profile

WS-I Basic Profile 1.1: SOAP 1.1 WSDL 1.1 Must use HTTP binding, should use HTTP 1.1 XML Schema Part 1, Part 2 May use HTTPS SOAP messages should use document/literal

V1.2 in draft form

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Web Services: Another approach to distributed computing

Transport

Messaging

Description

Discovery

Quality Of Service

Builds on the legacy of CORBA, J2EE etc It is not a new component model, programming

model or programming language. UDDI/WSDL/SOAP provide another

distributed computing technology Standards developing for the Quality of

Services and other EAI-type functionality. Exercise: Write down the standards for J2EE

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Web Services: Another approach to distributed computing

Transport

Messaging

Description

Discovery

Quality Of Service

HTTP, MQ, SMTP

XML

SOAP

XSD, WSDL, WS-Policy

UDDI

WS-Reliable

Messaging

WS-Security

WS-BA

WS-Coordination

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Web Services Strengths

Interoperability Based on open standards, utilizes existing infrastructure Can be accessed from any programming language/model

Ubiquity Communicates through XML/HTTP – Any system that supports

these standards, supports Web Services Support from all major software vendors (IBM and Microsoft)

Low barrier to entry Concepts easy to understand, easy to implement Toolkits allow COM, JEE, and CORBA components to be

exposed as Web Services

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Web Services and XML/WS standards Java API for XML Parsing (JAXP)

JAXP enables applications to parse and transform XML documents Independent of XML processor implementation

JAXP includes common industry standard components/interfaces DOM (Document Object Model and SAX (Simple API for XML Processing) XSLT (XML Style Language Transformations)

JAXP adds additional functionality beyond these standards Java API for XML Remote Procedure Call (JAX-RPC) SOAP (Simple Object Access Protocol) 1.1 specification

Java API for XML Registries (JAX-R) APIs to access UDDI Registry