Accessing and using .jsf files from the database

Question

What is the best way to enable my webapplication to use JSF files stored in the database? I'd like to be able to dynamically (during runtime) create new JSF pages which will be made available without having to redeploy the application.

So in other words: I would like to store the bigger part of my JSF pages in the database and would like JSF to use the database as a datasource for getting JSF files.

I've thought long about a solution and found some possible ways. However, I haven't been able to implement either of them.

1. Whenever a new page has to be added/removed: manipulate the files in the classpath (e.g. remove or add a file to the .war file)
2. Extending the classpath of the webapplication so it will be able to get files from an at runtime defined location (i.e. /tmp or directly using a database connection)
3. Provide JSF with a way to find resources another way ( this doesn't seem possible? )

My environment:

• Java SE 6
• Jetty as servlet container
• Mojarra as jsf implementation

Now, my question:

Is it possible for someone to let JSF find pages at a location other than the default classpath, preferably the database?

Any response is greatly appreciated!

Answer 1

Nice question. BalusC's answer is - as always - complete and right.

However, if your point is to create an application where gui is built dynamically, there is a way that might serve you better (depending on what you really want to achieve).

JSF views are similar to Swing forms - they are just a bunch of JavaBeans(tm) glued together. The big difference is that when a field is bound to an EL expression, you do not use standard accessors, but rather a special method (setValueExpression).

This means you can build your GUI from objects (the concrete classes can be found in javax.faces.component.html) in a pure programmatic way and then use binding attribute to show it on page. Something like:

<h:form>
    <h:panelGrid binding="#{formBuilder.component}"/>
</h:form>

And then in the managed formBuilder bean:

@PostConstruct
public void init() {
    HtmlInputText hit = new HtmlInputText();
    // properties are easy:
    hol.setStyle("border: 2px solid red");
    // binding is a bit harder:
    hit.setValueExpression("value", expression("#{test.counter}", String.class));

    HtmlOutcomeTargetLink hol = new HtmlOutcomeTargetLink();
    hol.setValue("link leading to another view");
    hol.setOutcome("whatever");

    component = new UIPanel();
    component.getChildren().add(hit);
    component.getChildren().add(hol);
}

private ValueExpression expression(String s, Class c){
    return FacesContext.getCurrentInstance().getApplication().getExpressionFactory().createValueExpression(
            FacesContext.getCurrentInstance().getELContext(),
            s, c
    );
}

The example above builds a static panel, but it would be possible to:

• create an object model of your GUI
• map the model to database (with hibernate or another orm)
• write some kind of adapter or bridge to build JSF objects from your object model
• make a managed bean that receives the form id, grabs the relevant form from database, builds a JSF panel out of it and presents it as a property, ready to be bound.

This way you could have just one static xhtml with a single tag and use it to present any number of dynamic forms.

As I said, this method could be better than just storing files, but not necessarily. If you just want to save yourself the hassle of redeployment, this is a huge overkill (then again, you do NOT need to redeploy JSF applications just to change forms). If on the other hand your goal is to have something like user-defined and edited forms, having a good object model and storing it in a proper way could be a good idea.

The bumps ahead would be:

• navigation (perhaps a custom navigation handler would suffice?)
• problems with generating plain html
• possibly some problems with lifecycle of view scoped forms

Answer 2

1: Whenever a new page has to be added/removed: manipulate the files in the classpath (e.g. remove or add a file to the .war file)

This is definitely possible if the WAR is expanded. I am not sure about Jetty, but it works for me with Mojarra 2.x on Tomcat 7 and Glassfish 3. Just writing the file to the expanded WAR folder the usual Java IO way suffices.

File file = new File(servletContext.getRealPath("/foo.xhtml"));

if (!file.exists()) {
    OutputStream output = new FileOutputStream(file);

    try {
        output.write(bytes); // Can be bytes from DB.
    } finally {
        output.close();
    }
}

This needs to be executed before the FacesServlet kicks in. A Filter is a perfect place. See also this related answer:

• How to create dynamic JSF form fields

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2: Extending the classpath of the webapplication so it will be able to get files from an at runtime defined location (i.e. /tmp or directly using a database connection)

You can package Facelets files in a JAR file and put it in the classpath and provide a Facelets ResourceResolver which serves the files from the JAR on when no match is found in WAR. You can find complete code examples in the following answers:

• how to share a jsf error page between multiple wars
• How to create a modular JSF 2.0 application?

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3: Provide JSF with a way to find resources another way ( this doesn't seem possible? )

You've plenty of play room in the custom ResourceResolver.