The question of the day comes from Mark Stephens, from JPedal (JPedal is the leading 100% Java PDF library, providing a Java PDF viewer, PDF to image conversion, PDF printing or adding PDF search and PDF extraction features), in the form of a screenshot:

The question is clear. By looking at the annotations above, you can see that Mark has an ActionListener that has been bound to the right-click popup menu on PDF files. Now he needs to get hold of the file to which the Action has been bound.

How, oh  how, can one get hold of that file? Well, it's simple. Leave everything you see above exactly as it is but change the Java code section to this:

 public final class PDF2JavaFXContext implements ActionListener {

    private final DataObject context;

    public PDF2JavaFXContext(DataObject context) {
        this.context = context;
    }

    public void actionPerformed(ActionEvent ev) {
        FileObject fo = context.getPrimaryFile();
        File theFile = FileUtil.toFile(fo);
        //do something with your file...
    }

} 

The point is that the annotations at the top of the class bind the Action to either Actions.alwaysEnabled, which is a factory method for creating always-enabled Actions, or Actions.context, which is a factory method for creating context-sensitive Actions. How does the Action get bound to the factory method? The annotations are converted, when the module is compiled, into XML registration entries in the "generated-layer.xml", which you can find in your "build" folder, in the Files window, after building the module.

In Mark's case, since the Action should be context-sensitive to PDF files, he needs to bind his PDF2JavaFXContext ActionListener (which should probably be named "PDF2JavaFXActionListener", since the class is an ActionListener) to Actions.context. All he needs to do that is pass in the object he wants to work with into the constructor of the ActionListener. Now, when the module is built, the annotation processor is going to take the annotations and convert them to XML registration entries, but the constructor will also be checked to see whether it is empty or not. In this case, the constructor isn't empty, hence the Action should be context-sensitive and so the ActionListener is bound to Actions.context.

The Actions.context will do all the enablement work for Mark, so that he will not need to provide any code for enabling/disabling the Action. The Action will be enabled whenever a DataObject is selected. Since his Action is bound to Nodes in the Projects window that represent PDF files, the Action will always be enabled whenever Mark right-clicks on a PDF Node, since the Node exposes its own DataObject.

Once Mark has access to the DataObject, he can get the underlying FileObject via getPrimaryFile and he can then convert the FileObject to a java.io.File via FileUtil.getConfigFile. Once he's got the java.io.File, he can do with it whatever he needs.

Further reading: http://bits.netbeans.org/dev/javadoc/