Reviewing External Resources and Legacy Systems
In an ideal world, your entire application might only contain Java components and applications, but it is not an ideal world. Very few architects have the opportunity to design entire Java systems from the ground-up, and very few enterprise developers have the opportunity to solely work on these types of systems. In reality, systems are heterogeneous in nature; that is, they are made up of many different parts. Figure 19.1 shows a complex heterogeneous environment that shows an array of clients attempting to access the services provided by a vast array of non-Java applications and systems.
Figure 19.1. A complex heterogeneous environment.
As you can see, the system consists of Enterprise Information Systems, such as ERP, SAP, and mainframe transaction processing systems. In addition, the enterprise services must call on the services provided by legacy code libraries, remote objects written in non-Java programming languages, and code written in lower-level programming languages.
The needs of business and the pressures of the application development cycle means that it is simply not feasible to rewrite all these elements so that they consist of pure Java. The only feasible option is that enterprise services provide mechanisms that integrate with these legacy and non-Java elements. Luckily, there are a number of Java technologies that allow you to integrate J2EE applications with these elements. It is these technologies that you will explore in today's lesson.