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Saturday, May 05, 2012

JSF 2 Tip of the Day: Programmatic PhaseListener

I had a use case where I needed to use a PhaseListener programmatically. I had originally tried to use a faces-config.xml to add the listener. I encountered a problem with an ear file which contained a war that contained a space. When Weblogic expanded the ear file it could not find the faces-config.xml since the path from expanded ear file had a space. Unfortunately, the program had too many dependencies to change to remove the space. So I decided to inject it. I was quite surprised to find that there was no annotation for PhaseListener in JSF 2.1.

Undaunted, I decided to figure it out. Admittedly, after I figured it out, I searched on Google, but everyone who had posted a solution did not a good example , or it was not quite as elegant as mine. I believe.

Specifically, my use case was to provide programmatic login where I use a PhaseListener to determine if the user is authenticated before restoring the view. This particular use case means that I must have the PhaseListener injected prior to responding to any requests. Fortunately, the JSF 2 API makes it very easy to do this.

The basic design is as follows:
  1. Use a @ManagedBean(eager=true) annotation. The eager attribute forces the container to load the bean immediately rather than lazy loading.
  2. Use the @ApplicationScoped annotation. This will allow us to set the PhaseListener for the whole application.
  3. Create a method which has a @PostConstruct annotation. This will allow us to set the listener immediately following the constructor.
    Note: You will want to follow this design so that if there are any annotations, they will be processed prior to adding the PhaseListener.
  4. Add the listener in the @PostConstruct method.

The JSF 2 API does a great job of explaining, how to use the LifecycleFactory to get a reference to the Lifecycle object. This is the key to adding the PhaseListener. If you are an API developer, this is a great example of documentation for people who want to use your API.

Code

The code for the project was developed using NetBeans 7.1.2 using Apache Maven. The code can be found here: programmatic-phaselistener.zip

ApplicationBean.java


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