Building Web Services with Java

1. Building Web Services with Java Neal Ford CTO, The DSW Group, Ltd. Tuesday, September 10, 2002

2. What This Session Will Cover: • Decrypting the alphabet soup of web services • SOAP • Axis • Configuration • Deployment of web services • Simple • Complex • XML <-> Java data mapping • WSDL • UDDI • Application integration • Interoperability

3. The Alphabet Soup • XML • Extensible Markup Language • SOAP • Simple Object Access Protocol • WSDL • Web Services Definition Language • UDDI • Universal Description Discovery and Integration

4. SOAP • Overview of SOAP • SOAP Envelope Framework • SOAP Envelope • SOAP Versioning • SOAP Headers • SOAP Body • SOAP Intermediaries • Defined • Uses • Crossing trust domains • Ensuring scalability • Providing value-added services along the message path

5. SOAP • Error Handling • SOAP Data Encoding • Specifying different encodings • Data encoding rules • SOAP protocol bindings • HTTP/HTTPS • SOAP with attachments • SOAP over SMTP

6. SOAP and Java • Working with XML in Java • XML parsing with Xerces • XSL/XSLT transformations with Xalan • Publishing Frameworks and Cocoon • Apache SOAP v2 • AXIS

7. Axis (Apache Extensible Interaction System • Where to get it • http://xml.apache.org/axis • Axis includes • a simple stand-alone server, • a server which plugs into servlet engines such as Tomcat, • extensive support for the Web Service Description Language (WSDL) • emitter tooling that generates Java classes from WSDL. • some sample programs • a tool for monitoring TCP/IP packets. • General Architecture

8. Axis Components • Axis Engine • Handlers • Chain • Transports • Deployment/configuration • Serializers/deserializers

9. Simple Web Services • Axis handles through JWS files • Axis • Locates the file • Compiles the class • Converts SOAP calls correctly into invocations of your Java class • Example – Simple Web Service

10. Custom Deployment and WSDD Files • Web Service Deployment Descriptor • XML document that defines deployment artifacts <deployment xmlns="http://xml.apache.org/axis/wsdd/" xmlns:java="http://xml.apache.org/axis/wsdd/providers/java">  <service name="MyService" provider="java:RPC">   <parameter name="className“ value="samples.userguide.example3.MyService"/>   <parameter name="allowedMethods" value="*"/>  </service> </deployment> • Deployed (and undeployed) with the AdminClient tool java org.apache.axis.client.AdminClient deploy.wsdd

11. More Advanced Deployment Options • WSDD files can specify specific details about the web service, including handlers and chains <deployment xmlns="http://xml.apache.org/axis/wsdd/"             xmlns:java="http://xml.apache.org/axis/wsdd/providers/java">   <!-- define the logging handler configuration -->  <handler name="track" type="java:samples.userguide.example4.LogHandler">   <parameter name="filename" value="MyService.log"/>  </handler>  <!-- define the service, using the log handler we just defined -->  <service name="LogTestService" provider="java:RPC">   <requestFlow>    <handler type="track"/>   </requestFlow>   <parameter name="className" value="samples.userguide.example4.Service"/>   <parameter name="allowedMethods" value="*"/>  </service> </deployment>

12. XML <-> Java Data Mapping with Axis • Automatic serialization/deserialization for JavaBeans <beanMapping qname="ns:local" xmlns:ns="someNamespace"              languageSpecificType="java:my.java.thingy"/> • It is also possible to write custom serializer/deserializers

13. WSDL (Web Services Description Language) • Primary elements of WSDL schema • PortType • Operation • Message • Binding • Port • Service • Definitions • Documentation

14. Axis Support for WSDL • Axis supports WSDL in three ways • Auto-generation of WSDL via the “?WSDL“ flag • WSDL2Java tool • Java2WSDL tool

15. WSDL2Java • Tool that generates Java stub classes from WSDL descriptions java org.apache.axis.wsdl.WSDL2Java (WSDL-file-URL)

16. WSDL2Java • Given: <xsd:complexType name="phone">   <xsd:all>     <xsd:element name="areaCode" type="xsd:int"/>     <xsd:element name="exchange" type="xsd:string"/>     <xsd:element name="number" type="xsd:string"/>   </xsd:all> </xsd:complexType> • WSDL2Java generates: public class Phone implements java.io.Serializable {     public Phone() {...}     public int getAreaCode() {...}     public void setAreaCode(int areaCode) {...}     public java.lang.String getExchange() {...}     public void setExchange(java.lang.String exchange) {...}     public java.lang.String getNumber() {...}     public void setNumber(java.lang.String number) {...}     public boolean equals(Object obj) {...}     public int hashCode() {...} }

17. Holders • JAX-PRC defines both in and inout parameters • Axis and WSDL2Java handle this by generating holder classes • Works like Helpers in CORBA package samples.addr.holders; public final class PhoneHolder implements javax.xml.rpc.holders.Holder { public samples.addr.Phone value; public PhoneHolder(){ } public PhoneHolder(samples.addr.Phone value) { this.value = value; } }

18. Java2WSDL • Provide a Java interface or class package samples.userguide.example6; /**  * Interface describing a web service to set and get Widget prices.  **/ public interface WidgetPrice {     public void setWidgetPrice(String widgetName, String price);     public String getWidgetPrice(String widgetName); }

19. Java2WSDL • Use Java2WSDL to create a WSDL file java org.apache.axis.wsdl.Java2WSDL -o wp.wsdl  -l"http://localhost:8080/axis/services/WidgetPrice" -n  "urn:Example6" -p"samples.userguide.example6" "urn:Example6"  samples.userguide.example6.WidgetPrice • Where: -o indicates the name of the output WSDL file -l indicates the location of the service -n is the target namespace of the WSDL file -p indicates a mapping from the package to a namespace. There may be multiple mappings. The class specified contains the interface of the webservice.

20. Java2WSDL • Create bindings using WSDL2Java java org.apache.axis.wsdl.WSDL2Java -o . -d Session -s -S true  -Nurn:Example6 samples.userguide.example6 wp.wsdl • Generated files

21. Java2WSDL • Generated files (continued)

22. UDDI (Universal Description Discovery and Integration) • UDDI (logical) registries • Business (businessEntity) • Reference types (tModel) • Business entity • White pages • Yellow pages • Green pages • Technical models • UDDI and Java

23. Retrofitting Existing Applications • Handling web services requirements • Statelessness • Granularity • Existing J2EE applications • Expose select functionality via web services • Web projects • Code must be written in web service calls to handle web service work • Can use either JWS deployment or custom deployment • EJB • Web services (accessed via Axis in the servlet layer) call stateless session beans to perform work • Session beans perform required work

24. Transaction Processing • If you already have EJB’s • Handled via normal transaction semantics via session and entity beans • If you have only servlets • Handled by code written in the web service methods exposed from the application • Two-phase commit is difficult across web service invocations • Impending transaction standards • TIP (Transaction Internet Protocol) • Simple 2-phase commit protocol over TCP/IP • XAML (XML Transaction Authority Markup Language) • Promising concept but still no specification

25. Interoperability • Cross language/framework/platform • Other Java web services • The .NET framework • Other languages/frameworks • Enforcing interoperability • SOAPBuilders • A very active Yahoo list of SOAP developers • Detailed discussions of interoperability issues • The Interoperability Lab • http://www.xmethods.net/ilab • Includes resources such as the SOAP validator test suite, standard ways to test web services

26. Tool Support • Example: Borland’s JBuilder Web Services Preview Kit • Integrates Axis into JBuilder • Wizards for • Creating SOAP Server • Importing WSDL • Exporting a class as a web service • Application Servers • BEA WebLogic • IBM Websphere • IONA XMLBus

27. Axis Alternatives • GLUE • Commercial product from Mind Electric, addresses the same space as Axis • Contains numerous features to make developing web services very easy • Customizable serialization/deserialization via decorated XMLSchema files • Custom XML parser (ElectricXML) • Java <-> XML persistence engine • Built in servlet engine • WASP • http://www.idoox.com • SOAP RMI • http://www.extreme.indiana.edu/soap

28. Web Services Reliability • Peter Deutsch’s Eight Fallacies of Distributed Computing • The network is reliable • Latency is zero • Bandwidth is infinite • The network is secure • Topology doesn't change • There is one administrator • Transport cost is zero • The network is homogeneous

29. The Future • Web services will be the defining paradigm for distributed computing in the near term • It is important that all web services interoperate successfully • Web services and Java • Full support from the open source and commercial communities • Built on top of an existing proven infrastructure (J2EE) • Very high scalability • Multiple vendor support • Cross platform • Tools are making it easier and easier to publish web services from Java applications, both J2EE and otherwise

30. Questions?To download samples:http://www.thedswgroup.com/conferences Neal Ford CTO The DSW Group, Ltd. nford@thedswgroup.com