Wicket and Spring

Sometime ago I was evaluating Wicket usefulness in development of lightweight, AJAX enabled UIs for web applications. Apache Wicket is modern framework for creating web UIs, well known for its original features as HTML/Java pages implementing separation between page view and logic. Other unique feature is global Application object, usually containing business logic entry points.


Wide range of modern applications requires complex, multi-tier backend (logic and storage, possibly remote, wired together with Web Services) and quite simple frontend (with few user actions available). Server part of the backend, along with WS clients is typically developed with Spring. As far as frontend is concerned, Wicket could be the solution to use.


There are many great Wicket manuals and tutorials, so I won't post any Wicket code here. Those interested can just take a look at Wicket Examples :) Other aspect is Wicket-Spring integration. After some research I decided to go with "central point" solution. This integration type assumes that all logic entry points (usually managers and DAOs) should be injected into Application object. Therefore all Pages have convenient access to the logic. This is compromise between annotations (performing all work under cover, without developer knowledge) and using no dependency injection at all. Because Application object is global (and singleton) it reminds somewhat hated Resource Locator solution, but for the sake of simplicity (remember, be agile..) I can accept it.


Required web.xml configuration is as follows:

<listener>
  <listener-class>
    org.springframework.web.context.ContextLoaderListener</listener-class>
</listener>
  
<filter>
  <filter-name>wicket.wicket-demo</filter-name>
  <filter-class>org.apache.wicket.protocol.http.WicketFilter</filter-class>
  <init-param>
    <param-name>applicationFactoryClassName</param-name>
    <param-value>
      org.apache.wicket.spring.SpringWebApplicationFactory
    </param-value>
  </init-param>
</filter>

With above entries in webapp config, developer is able to inject logic beans to the Applciation object without problems, as in following example:

<bean id="mrDaoBean" 
  class="apps.WicketMountains.data.MountainRecordDao">
  <property name="sessionFactory">
    <ref bean="sessionFactoryBean"/>
  </property>
</bean>
<bean id="mrManagerBean"
  class="apps.WicketMountains.data.MountainRecordManager">
  <property name="mrDao" ref="mrDaoBean"/>
</bean>
  
<!-- setup wicket application -->
<bean id="wicketApplication" 
  class="apps.WicketMountains.WicketApplication">
  <property name="mrManager" ref="mrManagerBean"/>
</bean>

Wicket components can access logic beans using code similar to call:

((WicketApplication)Application.get()).getMountainRecordManager()

One nice feature of the Wicket framework is bunch of ready to use AJAX components with exhaustive description of use. Beginner in Wicket (as myself) is able to develop first useful, pretty, AJAX enabled webapp in few hours only.