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| Writing a web application is not just about producing a good layout and a bunch of “cool” pages. We must also integrate our presentation code with enterprise resources like data sources, message queues, business objects, etc... |
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| The first decade of 2000s has seen the rising of new frameworks (like http://spring.io/[Spring] ) and new specifications (like http://en.wikipedia.org/wiki/Enterprise_JavaBeans[EJB 3.1] ) aimed to simplify the management of enterprise resources and (among other things) their integration with presentation code. |
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| All these new technologies are based on the concepts of container and dependency injection. Container is the environment where our enterprise resources are created and configured while http://en.wikipedia.org/wiki/Dependency_Injection[dependency injection] is a pattern implemented by containers to inject into an object the resources it depends on. |
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| Wicket can be easily integrated with enterprise containers using component instantiation listeners. These entities are instances of interface _org.apache.wicket.application.IComponentInstantiationListener_ and can be registered during application's initialization. IComponentInstantiationListener defines callback method onInstantiation(Component component) which can be used to provide custom instantiation logic for Wicket components. |
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| Wicket distribution and project https://github.com/wicketstuff[WicketStuff] already provide a set of built-in listeners to integrate our applications with EJB 3.1 compliant containers (like JBoss Seam) or with some of the most popular enterprise frameworks like http://code.google.com/p/google-guice/[Guice] or Spring. |
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| In this chapter we will see two basic examples of injecting a container-defined object into a page using first an implementation of the EJB 3.1 specifications (project http://openejb.apache.org/[OpenEJB] ) and then using Spring. |
