Creating an application updater

Question

Firstly, I'm not new to programming per say, but I'm certainly not accomplished by any means! I have limited knowledge to put it mildly and always worry I'm not doing it "right" (if there is a right way).
I know, JWS etc - I tried it, and one grumble was that my applications listener (I assume it was the action listener I had on the button) didn't work anymore - when clicking the button the file browser dialog box failed to appear (not an issue as long as it's not a webstart).
It also felt a bit of a cheat... I didn't know how to make an updater, just used an existing solution (I'm aware this may be an instance where JWS is the right way..). However, I wanted to try making one myself and so that's what I tried to do.
So I made one, but it took 2 Jar files. I'm sure there are more elegant solutions - hence the thread.
Currently - you start the application, you may check for updates. If one is available, you are given the option to update or not. If no update (or choose not to update), you continue.
If there is an update, the second Jar is executed, and the first one closes itself. This is because the second Jar displays a little interface showing the download progress, before essentially over-writing the first Jar's install with the new one. It then re-opens the main application, and exits itself (so now the updated application is running, and the updater is closed).
I feel this is bulky. Trying to overwrite a Jar currently in use failed though... is there a way to go about this so that I could just use one Jar file?
Does anyone have any suggestions for more elegant (or proper) solutions, without JWS is preferable as I prefer to learn how to do things, instead of using existing pre-packaged solutions. Yes, JWS looks great but it neither satisfied my curiosity nor my desire to learn how to do it myself.
Also, afaik, JWS keeps the program in Cache, instead of it's own location? I also had issues that one of my applications button has a listener that opens a file dialog browser. Works perfectly fine, until I tried JWS - at which point clicking the button does nothing, but unsure why!
Code? Too long to put in, but to give the gist of what happens:
This is the "check for updates" within the main application. The "check update" method returns true/false depending upon whether an update is available. Currently it checks a file on a server (which holds the version number of the application they may download) and a local file holding the current application installed version number. Is there a better way to check version numbers than read txt files? I couldn't locate anything that shows version numbers in my Jar's, maybe I'm missing something?
jMenuItem1.addActionListener(new ActionListener(){
           public void actionPerformed(ActionEvent e){
               if(checkUpdate()){// is there one?
                   if(showConfirmDialog("Would you like to update now?", "Update Available")){ // would they like to update?
                        String cmd = "javaw -jar updater.jar";
                        try {
                            Runtime.getRuntime().exec(cmd);
                        } catch (IOException ex) {
                            Logger.getLogger(FLScanner.class.getName()).log(Level.SEVERE, null, ex);
                    exit(); // close this application
                } else {
                   showMessage("No new update available", "Up to date!"); // display no update available
        });This is the updaters code, it has already downloaded the newest applications jar file (with a different name) and then performs this. It also updates the locally held version number with the new version number as well.
File oldFile = new File("Application.jar");
if(oldFile.exists()){
            oldFile.delete();
            File newFile = new File("Application_update.jar");
            newFile.renameTo(new File("Application.jar"));
            jLabel1.setText("Restarting Application...");
            try {
                Thread.sleep(1000); // gives chance for the rename to have occured before starting!!
            } catch (InterruptedException ex) {
                Logger.getLogger(Updater.class.getName()).log(Level.SEVERE, null, ex);
            String cmd = "javaw -jar Application.jar"; // command to run the new jar
            try {
                Process proc = Runtime.getRuntime().exec(cmd); // run it.
            } catch (IOException ex) {
                // handle this, somehow.
            this.dispose();// close the updaterI know there is insufficient error handling at present, but I thought it best to get some feedback if anyone is willing :)

Answer 1

Did you sign your jar file for JWS? I don't think the security manager will allow a filebrowser if the jar is not signed.
Edited by: Plee on Dec 29, 2008 6:54 AM