// 2009-04-20 Christian d'Heureuse (chdh@inventec.ch): Module created.

import java.io.File;
import java.lang.reflect.Method;
import java.net.URI;
import java.net.URL;
import java.net.URLClassLoader;
import java.util.List;
import javax.swing.JOptionPane;

public class JavaApplLauncher {

public List<String>                    classPath;                    // path names are relative to the directory of the JAR file of this class
public String                          mainClassName;
public boolean                         setCurrentDir = true;         // true = set current directory to JAR directory

private File                           baseDir;
private ClassLoader                    newClassLoader;

public boolean startAndDisplayError (String... args) {
   try {
      start (args); }
    catch (Throwable t) {
      t.printStackTrace();
      showErrorMessage ("Error: "+t.toString(), "Error while launching application");
      return false; }
   return true; }

private static void showErrorMessage (String msg, String title) {
   JOptionPane.showMessageDialog (null, msg, title, JOptionPane.ERROR_MESSAGE); }

public void start (String... args) throws Exception {
   baseDir = getBaseDir();
   if (setCurrentDir)
      System.setProperty ("user.dir", baseDir.getAbsolutePath());
   setClassLoader();
   callMainClass (args); }

private void setClassLoader() throws Exception {
   Thread thread = Thread.currentThread();
   ClassLoader parentClassLoader = thread.getContextClassLoader();
   if (parentClassLoader == null) parentClassLoader = JavaApplLauncher.class.getClassLoader();
   if (parentClassLoader == null) parentClassLoader = ClassLoader.getSystemClassLoader();
   URL[] cp = buildAbsoluteClassPath();
   newClassLoader = new URLClassLoader(cp, parentClassLoader);
   thread.setContextClassLoader (newClassLoader); }

private URL[] buildAbsoluteClassPath() throws Exception {
   URL[] cp = new URL[classPath.size()];
   for (int i=0; i<classPath.size(); i++)
      cp[i] = getAbsoluteUrl(classPath.get(i));
   return cp; }

private URL getAbsoluteUrl (String path) throws Exception {
   File f = new File(path);
   if (!f.isAbsolute())
      f = new File(baseDir, path);
   return f.toURI().toURL(); }

private void callMainClass (String[] args) throws Exception {
   Class<?> mainClass = Class.forName(mainClassName, true, newClassLoader);
   Method mainMethod = mainClass.getMethod("main", args.getClass());
   mainMethod.invoke (null, (Object)args); }

private File getBaseDir() throws Exception {
   URI uri = getClass().getProtectionDomain().getCodeSource().getLocation().toURI();
   if (!"file".equals(uri.getScheme()))
      throw new Exception ("Unexpected scheme in JAR file URI: "+uri);
   File f = new File(uri.getSchemeSpecificPart()).getAbsoluteFile();
   if (f.getName().endsWith(".jar")) f = f.getParentFile();
   return f; }

} // end class JavaApplLauncher