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Over the past three years, the Java 2 Platform, Enterprise Edition (J2EE) has evolved into the premiere server-side solution for reliable, scalable enterprise applications. In that same time, the standardization and explosive adoption of XML-based protocols have paved the way for Web services and spawned an industry-wide focus on cross-platform interoperability. This article explores the intersection of these two phenomena in the next release of the enterprise Java platform, J2EE 1.4.
Sun Microsystems is expected to finalize the J2EE 1.4 specification this fall, with highly anticipated vendor implementations hitting the market in first quarter 2003. Core technologies, including servlets, JSP (JavaServer Pages), and EJB (Enterprise JavaBeans), are being revised; however, most changes focus on integrating extensive XML support throughout the platform. The various specification revisions include a few hidden gems, like EJB 2.1's new container-managed timer service. But the most high-profile changes involve XML support and new Web services semantics within the J2EE client and server environments.
This article assumes some familiarity with basic J2EE, XML, and Web services concepts. Whether you're a project manager, Web application developer, or a hard-core middleware and distributed applications guru, this article provides a clear understanding of the enterprise Java platform's direction and how J2EE 1.4 will support emerging Web services standards.
Sun introduced the Java APIs for XML, or Java XML Pack, at JavaOne in June 2000, reintroduced them as part of the Web Services Developer Pack (WSDP) in summer 2001, and will include many of these APIs in the J2EE 1.4 platform this winter. The Java XML Pack enriches the Java platform with a wide spectrum of XML support. A brief recap of a Web service's lifecycle serves as a good template for understanding where each of the various Java APIs for XML fits into the J2EE platform.
Web services must provide their service's definition, usually in the form of a WSDL (Web Services Description Language) document. They also must advertise their availability in a registry such as UDDI (Universal Description, Discovery, and Integration) or ebXML, both of which are evolving through the nonprofit e-business consortium OASIS (Organization for the Advancement of Structured Information). Ultimately, Web services require runtime binding and RPC (remote procedure call)-style interaction, both synchronous and asynchronous. This involves the exchange, processing, and potential transformation of XML documents.
The Java API for XML-based RPC (JAX-RPC) is the backbone of J2EE 1.4's Web services support, offering a fairly complete Java-to-SOAP (Simple Object Access Protocol) abstraction with the RMI (Remote Method Invocation) programming model's familiar semantics. JAX-RPC also includes tools for generating a WSDL document from a Java Web services interface and vice versa. The Java API for XML Registries (JAXR) provides a pluggable abstraction for Web services registry operation, lookup, and interaction. Finally, the Java API for XML Processing (JAXP) is the glue that binds all things XML, giving J2EE portable APIs for XML processing with support for pluggable parsers and transformers.