Spring s Impacts on Application Portability

Spring's Impacts on Application Portability

All of the features discussed in this chapter are specific to Spring, and in many cases, are not available in other IoC containers. Although many IoC containers offer lifecycle management functionality, they probably do so through a different set of interfaces than Spring. If the portability of your application between different IoC containers is truly important, then you might want to avoid using some of the features that couple your application to Spring.

Remember, however, that by setting a constraint—that your application is portable between IoC containers—you are losing out on the wealth of functionality Spring offers. Because you are likely to be making a strategic choice to use Spring, it makes sense that you use it to the best of its ability.

Be careful not to create a requirement for portability out of thin air. In many cases, the end users of your application do not care if the application can run on three different IoC containers, they just want it to run. In our experience, it is often a mistake to try to build an application on the lowest common denominator of features available in your chosen technology. Doing so often sets your application at a disadvantage right from the get-go. However, if your application requires IoC container portability, then do not see this as a drawback—it is a true requirement, and therefore, one your application should fulfill. In Expert One-on-One: J2EE Development without EJB (Wrox, 2004), Rod Johnson and Jürgen Höller describe these types of requirement as phantom requirements and provide a much more detailed discussion of phantom requirements and how they can affect your project.

Although using these features may couple your application to the Spring framework, in reality, you are increasing the portability of your application in the wider scope. Consider that you are using a freely available, open source framework that has no particular vendor affiliation. An application built using Spring's IoC container runs anywhere Java runs. For J2EE applications, Spring opens up new possibilities for portability. Spring provides many of the same capabilities as J2EE and also provides classes to abstract and simplify many other aspects of J2EE. In many cases, it is possible to build a web application using Spring that runs in a simple servlet container, but with the same level of sophistication as an application targeted at a full-blown J2EE application server. By coupling to Spring, you can increase your application's portability by replacing many features that are either vendor-specific or rely on vendor-specific configuration with equivalent features in Spring.