Set default saving extension with JFileChooser

Question

I'm trying to save a file using JFileChooser. However, I seem to be having some trouble with it. Here's my code:

    if (e.getSource() == saveMenu) {

        JFileChooser chooser = new JFileChooser();
        chooser.setFileSelectionMode(JFileChooser.DIRECTORIES_ONLY);

        FileNameExtensionFilter xmlFilter = new FileNameExtensionFilter("xml files (*.xml)", "xml");
        // add filters
        chooser.addChoosableFileFilter(xmlFilter);
        chooser.setFileFilter(xmlFilter);

        int result = chooser.showSaveDialog(Simulation.this);

        if (result == chooser.APPROVE_OPTION) {
            writeToXML(chooser.getSelectedFile());
        }

    }

This doesn't force the file to have a .xml extension, so I've tried to use the following code to force the file to be saved with the extension .xml

     OutputFormat format = OutputFormat.createPrettyPrint();
     format.setEncoding("UTF-8");
     XMLWriter xmlWriter = null;
     try {              
         xmlWriter = new XMLWriter(new OutputStreamWriter(
                 new FileOutputStream(f+".xml"), "UTF8"),
                 format);

However, with this I can't prevent the user from writing xpto.xml in the JFileChooser and if they do that, the file will have "two extensions": it will be a file named xpto.xml.xml

So my questions are:

• How can I make the JFileChooser save an xml file by default?
• If the user inserts a file name like xpto.xml, how can I save it as xpto.xml and not xpto.xml.xml?

Answer 1

As you've noticed, JFileChooser doesn't enforce the FileFilter on a save. It will grey-out the existing non-XML file in the dialog it displays, but that's it. To enforce the filename, you have to do all the work. (This isn't just a matter of JFileChooser sucking -- it's a complex problem to deal with. Your might want your users to be able to name their files xml.xml.xml.xml.)

In your case, I recommend using FilenameUtils from Commons IO:

File file = chooser.getSelectedFile();
if (FilenameUtils.getExtension(file.getName()).equalsIgnoreCase("xml")) {
    // filename is OK as-is
} else {
    file = new File(file.toString() + ".xml");  // append .xml if "foo.jpg.xml" is OK
    file = new File(file.getParentFile(), FilenameUtils.getBaseName(file.getName())+".xml"); // ALTERNATIVELY: remove the extension (if any) and replace it with ".xml"
}

There's also some ideas for what to do if you want multiple types in the save dialog here: How to save file using JFileChooser?