Web Services (Nuts and Bolts)

ITEC 625 Web Development

Fall 2006

Reference:

Building Web Services with Java (Making sense of XML, SOAP, WSDL, and UDDI), “Web Services Basics Part I” (Chapters 1-6),Graham et al., Developers Library, 2004

Service-Oriented Architectures (SOAs)

Main roles• Service provider

• Service description

• Service requestor

• Service registry

Operations• Publish, find, bind

Why the fuss? SOA augments and grows your applications portfolio to a

portfolio of components (services and apps composed of services)

Organizations better able to construct software to integrate business processes and respond rapidly to changes in business environment.

Implicit, seamless software integration Approach makes it easier to focus on business processes

and tasks as services; less need to focus on underlying technical details of a service.

Easy selection of service interface design, most appropriate and existing IT investments for ease of building SOA, and best business processes.

Justifying Web Services

Application integration is faster, cheaper Many options for integration using many types

of devices (PDAs, cell phones, desktops, etc) Time to market is reduced Use of standards provides benefits (choice of

tools, more vendor options) Relatively low cost of entry Interface-based development reduces time to

integrate applications

Web Services vs. SOA

Associated but distinct. SOA

• An architectural concept, approach to building systems that focuses on loosely coupled set of component services that can be dynamically composed.

Web Services• One approach to building an SOA, providing a

standard for a particular set of XML-based technologies that can be used to build SOA systems.

XML

Document-centric vs Data-centric Instances (prolog, elements, attributes) Namespaces Schemas

• Well-formed, iaw rules of XML syntax

• Valid, iaw DTD or Schema

• Parsers can be validating/non-validating

• If Valid, then well-formed

XML Processing Pull parsing: application asks parser to give it the next

piece of info about the doc Push parsing, event-based parsing: parser sends info to

application about XML doc pieces encountered during the parse, sent in order, as they appear. Simple API for XML (SAX v. 2.0)

One-step parsing, DOM parsing. Parser reads whole document, generates a data structure (tree), deeply nested; DOM is language and platform independent. Don’t map well to native data structures, thus JDOM (Java DOM) for simplifying manipulation of doc trees in Java

Hybrid parsing, combinations Issues: Memory efficiency, computational efficiency, ease

of programming Also JAXP, Java API for XML Processing, version 1.2

XML Resources DOM Level 1, 2

• http://www.w3.org/TR/REC-DOM-Level-1 or 2 JAXB

• http://java.sun.com/xml/downloads/jaxb.html JAXP

• http://java.sun.com/xml/xml_jaxp.html JDOM

• http://www.jdom.org/docs/apidocs JSP1.2

• http://java.sun.com/products/jsp SAX

• http://www.saxproject.org/ XML, XML Namespaces, XML schema

• http://www.w3.org/TR/REC-xml• http://www.w3.org/TR/REC-xml-names• http://www.w3.org/TR/xmlschema-0/ or 1 or 2

SOAP Protocol

Version 1.2 Two parts for spec

• Part 1, the Messaging framework, central foundation

• Processing model

• Extensibility model

• Message structure

• Part 2, the Adjuncts

• Optional

• But give enough to developers (core of Part 1 is not enough)

SOAP Resources XML Protocol Working Group

• http://www.w3.org/2000/xp/Group SOAP 1.2 and Primer

• http://www.w3.org/TR/SOAP

• http://www.w3.org/TR/2003/REC-soap12-part0-20030624/ SOAP with attachments

• http://www.w3.org/TR/SOAP-attachments MTOM

• http://www.w3.org/TR/soap12-mtom/ XOP

• http://www.w3.org/TR/xop10/

Describing Web Services

WSDL is an IDL (Interface Description Language)

A WSDL description describes:• What a service does, operations (methods),

data needed (arguments and returns)

• How a service is accessed, data formats and protocols, etc .

• Where a service is located, URL, etc.

Major elements of WSDL

portTypemessagetypesbindingportservice

WSDL Resources

WSDL 1.1 and 2.0• http://www.w3.org/TR/wsdl

• http://www.w3.org/2002/ws/desc/wsdl20

WS-Policy and PolicyAttachment• http://www-106.ibm.com/developerworks/library/ws-pol

fram/

• http://www-106.ibm.com/developerworks/library/ws-polatt/

Implementing Web Services with Apache Axis

One of best Java-based Web services engines

One of most extensible, can be tuned to support new versions of SOAP

Can run on top of simple servlet engine or a full-blown J2EE application server

http://ws.apache.org/axis

Axis Resources Apache Axis

• http://ws.apache.org/axis Log4j

• http://logging.apache.org/log4j/docs/ Jakarta Discovery library and commons

• http://jakarta.apache.org/commons/discovery/

• http://jakarta.apache.org/commons/net/ JUnit

• http://junit.org SOAP builders

• http://groups.yahoo.com/group/soapbuilders

Discovering Web Services

Request copy of service description directly from provider

Centralized service registry (UDDI) Other publication and service discovery

mechanisms• At service provider’s point of offering

• Using WS-Inspection specification (see resources)

• Public repository of WSDL documents• http://www.salcentral.com

• http://www.xmethods.com

UDDI Datatypes

businessEntitybusinessServicebindingTemplatetModelpublisherAssertion

Using a UDDI Registry A UDDI registry is itself an example of a Web Service Entries in the registry can be published and queried using

a SOAP-based interface SOAP-based interface is used for all publish and query

operations Publishing usually requires registration and authentication

token for creating, updating, deleting entries in the registry

For publishing…Each datatype uses Save API and Delete API

For inquiry… Each datatype uses Find API and Get API

WSDL Service Interface Definitions for UDDI Registry

Inquiry API v2.0• http://uddi.org/wsdl/inquire_v2.wsdl

Publication API v2.0• http://uddi.org/wsdl/publish_v2.wsdl

API v3.0 portTypes• http://uddi.org/wsdl/uddi_api_v3_portType.wsdl

API v3.0 Bindings• http://uddi.org/wsdl/uddi_api_v3_binding.wsdl

UDDI Resources UDDI specs

• http://www.oasis-open.org/committees/uddi-spec/doc/tcspecs.htm

UDDI best practices• http://www.oasis-open.org/committees/uddi-spec/doc/bps.ht

m UDDI technical notes

• http://www.oasis-open.org/committees/uddi-spec/doc/tns.htm

WS-Inspection• http://www-106.ibm.com/developerworks/webservices/

library/ws-wsilspec.html