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Web Services (Nuts and Bolts)

This reference guide explores the fundamentals of building web services using Java, including XML, SOAP, WSDL, UDDI, and Apache Axis. It covers the main roles and functionalities of web services and service-oriented architectures (SOAs), justifying the use of web services for application integration and the advantages they offer. The guide also discusses XML processing, SOAP protocol, and describing web services using WSDL.

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Web Services (Nuts and Bolts)

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  1. 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

  2. Service-Oriented Architectures (SOAs) • Main roles • Service provider • Service description • Service requestor • Service registry • Operations • Publish, find, bind

  3. 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.

  4. 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

  5. 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.

  6. 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

  7. 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

  8. 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

  9. 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)

  10. 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/

  11. 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.

  12. Major elements of WSDL • portType • message • types • binding • port • service

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

  14. 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

  15. 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

  16. 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

  17. UDDI Datatypes • businessEntity • businessService • bindingTemplate • tModel • publisherAssertion

  18. 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

  19. 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

  20. 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.htm • 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

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