J2EE Design Patterns

Chapter 11. Messaging

Your application is done. Time to sit back and relax, right? Well, generally, no. You see, there’s this thing that people in business tend to do when confronted with new applications. “Wonderful,” they say. “Now can we connect it with our other system?” And the dance of development begins again.

In fact, the future often arrives before the application is even finished. More and more, the usefulness of any given system depends on how well it can connect to other systems, sharing data and participating in ever more elaborate processes. Sometimes every system is shiny and modern, and all the interactions take place directly in Java. But usually many of the systems are old, incompatible, or both: they could include COBOL, thick Client/Server, and even Java and .NET applications created by other developers or spread across many organizations and isolated by heavy-duty firewalls. Each of these systems has different interfaces and different data formats. Some are always accessible, and some are available only transiently. Some interactions are vitally time sensitive, and some aren’t. It’s like a railway through a jungle—hard enough to navigate to begin with, but even worse when most of the tracks are a different gauge. The task of the enterprise integrator is to keep the traffic moving effectively.

In earlier chapters, we talked about remote procedure calls and web services as an approach for addressing integration issues. This chapter focuses on solving these problems ...