Java is an outstanding language for building components, services, and many applications that are vendor and platform neutral. The vast adoption of Java technology by the industry in the past decade is a testament to the power of Java. Development of new applications, services, and components using Java is not going away, but many organizations have progressively moved to the next phase in maturing their IT Infrastructure. This phase is driven by many factors including how businesses operate today, having to constantly adjust to market trends, and that IT has moved from being a support organization to being the backbone of business and, hence, needs to keep pace with the organization. Continuous and faster alignment with changing business needs, time-to-market, and cost are the factors that determine success in this phase.

There are some technologies that are starting to play a critical role in this phase, for example, service-oriented architecture (SOA) is a key enabler. Java EE technology is a natural service-enabler of existing applications, thereby forming the foundation of SOA. Service-enabled applications create the opportunity to compose functions from disparate and cross-functional applications to model business processes that transcend application and enterprise boundaries. Web Services Business Process Execution Language (WS-BPEL) provides a faster way to compose and orchestrate services by reuse. Java and WS-BPEL complement each other perfectly and provide a solid foundation for integrating services and delivering composite applications.

This article will briefly explain what these technologies are and how they can work together to improve developer productivity and business agility.

The Technologies - Java, WS-BPEL, and SOA
There are no globally accepted definitions for the technologies that this article will explore. So let's clarify them now as a common understanding is needed before getting into the details.

Service-oriented architecture is a technical pattern for implementing cohesive and loosely coupled business and technical functions with well-defined interfaces. Such services are consumed through the details specified in the interface and without any knowledge about the implementation.

While the SOA-based infrastructure model shown in Figure 1 has a few, but well-defined, layers of services, in reality there may be many more layers, as the services are reused and composed to create coarser-grained services. As illustrated in the diagram, services can consume each other to provide layers of services and such a model can be implemented using any language including Java. The service is not technology-dependent as long as it can be consumed through the well-defined interface. Java EE 5 is a set of coordinated technologies that enable solutions for developing, deploying, and managing server-centric applications. WS-BPEL is an XML-based execution language that can be used to compose the coarse-grained services into broader services or complete applications.

Tough Decisions
Technology without the right set of tools often does more damage than good. Identifying the right set of tools for a technology is as important as choosing the technology.

The science of delivering composite applications becomes more of an art when architects try to understand when to switch from Java to WS-BPEL. This decision often determines the agility of the composite application.

The Right Set of Tools
Sun Microsystems provides a bundle of tools and servers that we will be using for this article to build our composite application, specifically the Java EE 5 SDK Update 2 Tools Bundle. This can be found at http://java.sun.com/javaee/downloads/ and includes:

• Java EE 5 Application Server
• NetBeans 5.5 with NetBeans Enterprise Pack 5.5
• Java Business Integration (JBI) runtime and WS-BPEL Service Engine

In effect this bundle provides the capability to support the complete life cycle to develop, deploy, and manage applications and business processes, composing services from Java EE applications and Web services.

Putting the Technology into Action Use Case
To put the technology and the tools in context, let's take a scenario that you must be very familiar with, a scenario in which a new external-facing application is being developed iteratively by reusing functions from existing Java EE applications and external Web services.

In the architecture depicted in Figure 2, there are three existing Java EE Applications: 1) the Performance Evaluator - provides evaluations on the fiscal performance of existing customers; 2) the Vehicle Information Server - evaluates market conditions and vehicle history and serves a detailed report on the worthiness of the vehicle; and 3) the Financial Index Server - provides the current running rates and values that should be used to compute the loan details.

The new application should provide a service to receive loan applications over the Web and respond with a decision. The loan decision should be arrived at by applying predefined processing rules on the following data: 1) applicant's financial worthiness, 2) vehicle's value, 3) loan amount, and 4) current policies and indices for loans.

Design
The new application could be completely implemented in Java technology with just servlets, JSPs, EJBs, and POJOs. However, WS-BPEL is a more suitable language for service composition and business process execution. As mentioned earlier, the decision about when to start composing services using WS-BPEL can be tricky. The general rule is that Java can be used for extending existing services or composing fine-grained Java EE services to create more services that may not yet provide a cohesive and complete business or technical function. Should the new processing unit implement business or technical logic, which is more than invoking services and basic data transformations between invocations, that's an indication that it may be more suitable to implement Java. However, when the application or composition needed is process-centric and involves invoking services and hooking them together with flow logic and simple mappings, WS-BPEL may be the best way to implement this layer of the application.

The new application requires the development of the following services: 1) Applicant Evaluator - a service that aggregates an internal report if the applicant is an existing customer with an external credit report; 2) Loan Approval Processor - a service that takes an applicant's fiscal performance, vehicle report, and current indicators and comes up with a decision; and 3) the Vehicle Loan Application Process that will be exposed to the external world. This process will receive an incoming credit application, invoke the Applicant Evaluator Service, Vehicle Information Service, and Financial Index Service in that order and pass the results from all these services to the Loan Approval Processor service and return the decision to the caller.