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The application programming model (APM) is a J2EE programming model that provides guidelines to an application component provider. JPM is used to build software for business functions based on the functionality and system requirements that business requires.
A J2EE APM focuses on creating components to access a company's enterprise information system (EIS) and establish and manage connections to that system. APM also strives to develop components that can provide security to the enterprise application and support secure transactions.
The APM defines an outline for developing Web-centered, distributed and Java-based applications.
An APM outlines the best practices for building a J2EE enterprise application, most of which are based on a three-tier model:
A bank can be used as a simplified example of a three-tier structure. Teller machines (PCs) serve as the first tier. The mainframe is the third tier and the storage facility for the most critical data. Although the bank’s IT department manages these computers, it is not always possible to upgrade systems deploying the latest applications, due to the potential for data loss and/or other issues.
However, based on APM guidelines, a solution may be employed with Web/application servers and distributed component containers as middle-tier machines. With this middle tier, new functionalities can be provided to the first and third tiers without upgrading the first and third-tier systems or installing new software. By defining the middle tier, APM supports a movement toward thin Web-based clients.
Another important APM concept is the container. The major difference between JavaBean and J2EE components is that J2EE components do not often interact with each other, but do interact with their respective containers.