CODEWITHSUNDEEP
javajarexternal
nrubin29
nrubin29

Reputation: 1612

Execute an External JAR

I wrote a launcher for my game that, when given a valid username and password, will download a JAR file from a website if the file does not already exist or an update is available. The login system and file download work, but how do I run the downloaded JAR file?

I have tried Runtime.getRuntime().exec("java -jar " + file.getAbsolutePath());, but to no avail.

Thanks for the help!

downloading = new JLabel("Download AudioRPG executable from server. This may take up to a minute.");
                            downloading.setHorizontalAlignment(SwingConstants.CENTER);

                            Thread th = new Thread(new Runnable() {
                                public void run() {
                                    remove(username);
                                    remove(password);
                                    remove(submit);
                                    remove(remember);
                                    add(downloading, BorderLayout.CENTER);
                                    pack();

                                    try {
                                        FTPClient client = new FTPClient();

                                        client.connect("audiorpg.net");
                                        client.login("audiorpg", "mcpogotime1");
                                        client.changeDirectory("files");
                                        client.download("AudioRPG.jar", exe);
                                        client.disconnect(true);
                                        downloading.setText("Done! Launching AudioRPG...");
                                    }
                                    catch (Exception e) { e.printStackTrace(); }
                                }
                            });

                            th.start();

                            startExternalJAR(getClass(), th, exe);

private static void startExternalJAR(Class<?> c, Thread th, File exe) {
        if (!th.isAlive()) {
            try {
                final String mainClass;
                final JarFile jarFile = new JarFile(exe);
                try {
                    final Manifest manifest = jarFile.getManifest();
                    mainClass = manifest.getMainAttributes().getValue("Main-Class");
                } finally {
                    jarFile.close();
                }
                final URLClassLoader child = new URLClassLoader(new URL[]{exe.toURI().toURL()}, c.getClassLoader());
                final Class<?> classToLoad = Class.forName(mainClass, true, child);
                final Method method = classToLoad.getDeclaredMethod("main", String[].class);
                final Object[] arguments = {new String[0]};
                method.invoke(null, arguments);
            }
            catch (Exception ex) { ex.printStackTrace(); }
        }
        else {
            try { Thread.sleep(1000); }
            catch (Exception e) { }
            startExternalJAR(c, th, exe);
        }
    }

That is the code I am attempting to use now, but it is not working. @Boris the Spider any tips?

Upvotes: 2

Views: 6360

Answers (2)

Boris the Spider
Boris the Spider

Reputation: 61128

You should use the URLClassLoader to load the jar and then call main.

final String mainClass;
final JarFile jarFile = new JarFile(file);
try {
    final Manifest manifest = jarFile.getManifest();
    mainClass = manifest.getMainAttributes().getValue("Main-Class");
} finally {
    jarFile.close();
}
final URLClassLoader child = new URLClassLoader(new URL[]{file.toURI().toURL()}, this.getClass().getClassLoader());
final Class classToLoad = Class.forName(mainClass, true, child);
final Method method = classToLoad.getDeclaredMethod("main", String[].class);
final Object[] arguments = {new String[0]};
method.invoke(null, arguments);

Taken from this SO answer.

Upvotes: 0

Rag
Rag

Reputation: 6593

Don't execute the jar like a command. Load the class you want from the jar using the classloader and then instantiate it.

http://docs.oracle.com/javase/tutorial/deployment/jar/jarclassloader.html

  1. Load the jar by constructing a new JarClassLoader("url goes here").
  2. Call .invokeClass("MyMainClassName", new String[] { "Args", "Go", "Here" }) on the JarClassLoader.

Upvotes: 4

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