Bug 91072 F2/Hover for external javadoc does not work
org.eclipse.jdt.ui/ui/org/eclipse/jdt/internal/ui/preferences/JavadocConfigurationBlock.java
public void spawnInBrowser(URL url) {
			OpenBrowserUtil.open(url, fShell.getDisplay(), fTitle);
		}
		private void validateFile(URL location) throws MalformedURLException {
			File folder = new File(location.getFile());
			if (folder.isDirectory()) {
				File indexFile= new File(folder, "index.html"); 
				if (indexFile.isFile()) {				
					File packageList= new File(folder, "package-list"); 
					if (packageList.exists()) {
						if (MessageDialog.openConfirm(fShell, fTitle, fValidMessage)) { 
							spawnInBrowser(indexFile.toURL());
						}
						return;					
					}
				}
			}
			MessageDialog.openWarning(fShell, fTitle, fInvalidMessage); 
		}
		
		private void validateURL(URL location) throws MalformedURLException {
			IPath path= new Path(location.toExternalForm());
			IPath index = path.append("index.html"); 
			IPath packagelist = path.append("package-list"); 
			URL indexURL = new URL(index.toString());
			URL packagelistURL = new URL(packagelist.toString());
			InputStream in1= null;
			InputStream in2= null;
			try {
				in1= indexURL.openConnection().getInputStream();