XML, Web Services, and the Data Revolution

By Frank  P.  Coyle

J2EE is a standard for building robust enterprise applications based on an evolving vision of application-server technology centered around the Java programming language. It has historically been used to build Web sites and applications around Enterprise JavaBeans (EJB). Recently it has been extended to include support for XML and Web services.

While J2EE originated with Sun, changes to the J2EE specification are under the collaborative umbrella of the Java Community Process with input from vendors who have J2EE-compliant server products. Also as part of the Java Community Process, Sun is rolling out its Web Services Pack, a combination of applications and APIs designed to integrate Sun's Java programming language with XML and Web services. The Web Services Pack, illustrated in Figure 6.4, includes the following APIs:

• Java API for XML Processing (JAXP): JAXP gives developers flexibility by letting them easily swap out XML parsers, which they may want to do if a parser that performs better for their application becomes available. Without JAXP, it's easy to get locked into one vendor's XML parser.

• Java Architecture for XML Binding (JAXB): JAXB is a Java API and toolset for creating two-way mapping between XML documents and Java objects. JAXB simplifies the task of going from an XML document type definition or schema and creating a program to process a conformant XML document. For example, an XML schema for mortgage banking created by the Mortgage Industry Standards Maintenance Organization (MISMO) is used by the mortgage industry to exchange loan information. JAXB enables the creation of Java classes from the schema that will support the processing of XML data encoded in the MISMO format. Prior to JAXB, programmers were required to write Java code to format the parsed XML data into Java objects based on the XML schema. JAXB greatly simplifies the process, which was complex, error prone, and often not portable.

• Java API for XML Messaging (JAXM): JAXM is designed to allow access to emerging XML messaging standards such as Electronic Business XML (ebXML) Transport/Packaging and Routing. It typically will be used along with JAX-RPC, which will give Java programmers a single interface to any XML-based Remote Procedure Call (RPC) mechanism, including the SOAP standard. Although SOAP is the acknowledged XML transport standard for Web services, developers using JAX-RPC will be better able to switch to any future XML-based RPC mechanism.

• Java API for XML Remote Procedure Calls (JAX-RPC): JAX-RPC is the API for doing XML-based procedure calls via XML-RPC in Java. XML-RPC allows one network node to execute code on another node by transferring XML data. XML-RPC is discussed in detail in Chapter 4.

• Java API for XML Registries (JAXR): JAXR provides a uniform standard interface to registries of XML business data such as the UDDI protocol. JAXR simplifies the development of e-business applications that can register and extract data from various registries, including those used with the ebXML modular business framework for global e-commerce.

Vendors with server products that are based on J2EE include Sun, IBM, BEA, Oracle, and HP. Each vendor provides additional features not found in the J2EE specification, which may create problems for organizations looking to switch J2EE vendors. In the following sections, we'll look at how some vendors have used J2EE to integrate their application server offerings with the world of Web services.

Sun ONE and Web Services

Sun has been quick to respond to Microsoft's embrace of XML and Web services (although it can be argued that Sun's initial cautious attitude toward XML is attributable to its solid positioning on the code side of the code-data divide discussed in Chapter 1). Sun's answer to Microsoft's .NET is Sun ONE, the Sun Open Net Environment, a framework for creating and deploying Web services from Sun's J2EE framework. Sun ONE is intended to be a template for interoperability between various devices and networks, bridging the gap between the loosely coupled Web and more tightly coupled object frameworks. To bring things together it relies on XML, SOAP, and Java to add Web services extensions from within J2EE. For developers, this means that from a Sun perspective Web services will be built using servlets, Java Server Pages, and EJB technology.

The integration of Web services with more conventional middleware offerings is based on Sun's iPlanet integration platform that incorporates Java, SOAP, and XML and supports message queuing for asynchronous message routing between disparate applications.