Untangling Enterprise Java

Abstract

S eparation of concerns is one of the oldest concepts in computer science. The term was coined by Dijkstra in 1974. 1 It is important because it simplifi es software, making it easier to develop and maintain. Separation of concerns is commonly achieved by decomposing an application into components. There are, however, crosscutting concerns, which span (or cut across) multiple components. These kinds of concerns cannot be handled by traditional forms of modularization and can make the application more complex and diffi cult to maintain. Examples of crosscutting concerns in enterprise Java applications include transaction management, security, persistence, and application assembly. Scattering the code that handles those concerns across multiple components is undesirable, however. This is because doing so would make each component more complex. Also, duplicating code in multiple modules can cause maintenance problems. Consequently, there has been a fl urry of activity in recent years to develop frameworks and new forms of modularity that try to untangle these crosscutting concerns from the application's business logic. In this article we look at the evolution of enterprise Java frameworks that tackle crosscutting concerns. We address how dissatisfaction with the fi rst-generation frameworks, which were based on the EJB (Enterprise JavaBeans) programming model, prompted the development of dramatically better frameworks. These newergeneration frameworks are based on the POJO (Plain Old Java Object) programming model. Even though the focus of this article is Java, it contains many useful lessons for developers of frameworks and applications written in other languages.

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“…The translation process adds annotations by matching PBSE regular expression patterns against program constructs. Figure 8 demonstrates the translator's process flow, in which input files-a set of Plain Old Java Objects (POJOs) [25] and PBSE metadata-parameterize the translator, and annotated POJOs serve as an intermediate build step. Once the automatically annotated files are compiled, they can be deployed to be executed by their respective frameworksmost modern frameworks do use annotations as their metadata format.…”

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“…Separation of Concerns (SoC) [14] is both a principle and a process for building software systems, which states that each constituent part of a system should be free of behaviors not inherent to its functional nature. Traditionally, SoC has been achieved by using modularity, encapsulation and information hiding techniques in the context of object-oriented programming, or layered designs Permission to make digital or hard copies of all or part of this work for personal or classroom use is granted without fee provided that copies are not made or distributed for profit or commercial advantage and that copies bear this notice and the full citation on the first page.…”