Re: URLClassLoader ClassNotFoundException
"Andreas Wollschlaeger" <postmaster@1.0.0.127.in-addr.arpa> wrote in message
news:euhbte$4g2$1@tantalos.rbi.informatik.uni-frankfurt.de...
Well, this sounds pretty sound, and is quite similar to some bootstrap
loader i wrote lately.
Did you pass the parent classloader to your homegrown classloader?
Yep
Otherwise you might be in trouble if some class cannot be loaded because
it cannot resolve its reference to some class from the java runtime.
Here is a snippet of code from something similar i wrote a while ago:
//
// Build a new ClassLoader using the given URLs, replace current
Classloader
//
ClassLoader oldCL =
Thread.currentThread().getContextClassLoader();
ClassLoader newCL = new URLClassLoader(myClasspathURLs, oldCL);
Thread.currentThread().setContextClassLoader(newCL);
System.out.println("Successfully replaced ClassLoader");
and then used
Class fooClass = newCL.loadClass(appClass);
along with some reflection wizardry to launch my application.
Almost identical to mine, but above don't work either :-(
Maybe its also worth a try to launch your application using the "-verbose"
switch, sometimes this gives a better hint why a class cannot be
loaded....
Yielded nothing useful.
I hope I don't have to go down the Runtime exec route but it's looking that
way :-(
Heres the code for what its worth to anyone 'au fait' with this kind of
thing who may shed light.
Compilable if you take out the utils.Log.ln() logging
import static utils.Log.ln;
import java.io.BufferedInputStream;
import java.io.BufferedOutputStream;
import java.io.BufferedReader;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.MalformedURLException;
import java.net.URL;
import java.net.URLClassLoader;
import java.net.URLConnection;
import java.util.ArrayList;
import java.util.Date;
import java.util.List;
import java.util.prefs.Preferences;
public class VersionUpdater {
private Preferences preferences;
private Date lastUpdated;
private List<URL> localJars;
private static final String
RESOURCES_KEY = "stitch-update-resource-url",
LAST_UPDATE_KEY = "stitch-last-update-time";
public VersionUpdater() throws Exception {
localJars = new ArrayList<URL>();
preferences = Preferences.systemRoot();
lastUpdated = getLastUpdate();
ln("Last updated: " + lastUpdated);
}
// pass in fallback resource
public boolean update(String updateResource) throws Exception {
boolean updated = false;
URL localUrl = getResourceAsUrl(updateResource);
// read the remote urls
List<URL> remoteUrls = readRemoteUrls(localUrl);
// iterate the urls and save each ones content
boolean first = true;
for (URL url : remoteUrls) {
if (first) {
saveResourceAsUrl(url);
first = false;
} else {
if (updateResource(url)) updated = true;
}
}
saveLastUpdate();
return updated;
}
public ClassLoader createClassLoader(ClassLoader parent) {
URLClassLoader loader = new URLClassLoader(
localJars.toArray(new URL[localJars.size()]), parent);
return loader;
}
private Date getLastUpdate() {
Long longTime = preferences.getLong(LAST_UPDATE_KEY, 0);
return new Date(longTime);
}
private void saveLastUpdate() {
Long longTime = new Date().getTime();
preferences.putLong(LAST_UPDATE_KEY, longTime);
}
private URL getResourceAsUrl(String url) throws MalformedURLException {
url = preferences.get(RESOURCES_KEY, url);
return new URL(url);
}
private void saveResourceAsUrl(URL url) {
preferences.put(RESOURCES_KEY, url.toExternalForm());
}
private List<URL> readRemoteUrls(URL url) throws IOException {
URLConnection connection = url.openConnection();
BufferedReader br = new BufferedReader(
new InputStreamReader(connection.getInputStream()));
return readUrls(br);
}
private List<URL> readUrls(BufferedReader reader) throws IOException {
List<URL> urls = new ArrayList<URL>();
String line;
while ((line = reader.readLine()) != null) {
try {
URL url = new URL(line.trim());
urls.add(url);
}
catch (MalformedURLException ex) {}
}
reader.close();
return urls;
}
private boolean updateResource(URL url) throws Exception {
boolean isUpdated;
URLConnection connection = url.openConnection();
Date modTime = new Date(connection.getLastModified()); // zero is possible
ln("Resource: " + url + " - updated: " + modTime);
String urlPath = url.getPath();
int idx = urlPath.lastIndexOf('/');
String name = urlPath.substring(idx+1);
URL resource = getClass().getResource("/" + name);
// if the servers version is more recent than last update time
// or we don't have any copy of the resource
if (modTime.after(lastUpdated) || resource == null) {
ln("Saving resource: " + name + " create? " + (resource == null));
BufferedOutputStream bos =
new BufferedOutputStream(new FileOutputStream(name));
BufferedInputStream bis = new BufferedInputStream(
connection.getInputStream());
byte [] buf = new byte[1028];
int i = 0;
while((i = bis.read(buf)) != -1) bos.write(buf, 0, i);
bos.flush();
bis.close();
bos.close();
resource = getClass().getResource("/" + name);
URLConnection c = resource.openConnection();
ln ("lasy mod chcks access: " + c.getLastModified());
isUpdated = true;
} else isUpdated = false;
//resource = new URL("jar:file:///" + name + "!/");
//ln(new File(name).getCanonicalPath());
ln("adding resource: " + resource);
if (resource != null) localJars.add(resource);
return isUpdated;
}
}
import static utils.Log.ln;
import java.net.URLClassLoader;
import javax.swing.JOptionPane;
public class Runner {
private static final String RESOURCE =
"http://foo/bar/update-resources.txt";
public static void main(String[] args) {
if (!runMainApp(null)) {
try {
VersionUpdater updater = new VersionUpdater();
updater.update(RESOURCE);
ClassLoader oldCl = Thread.currentThread().getContextClassLoader();
ClassLoader loader = updater.createClassLoader(oldCl);
Thread.currentThread().setContextClassLoader(loader);
runMainApp(loader);
}
catch (Exception ex) {
JOptionPane.showMessageDialog(null,
"An error occurred whilst attempting software update.\n" +
ex.getClass().getName() + "\n" +
ex.getLocalizedMessage(),
"Update Error", JOptionPane.ERROR_MESSAGE);
ex.printStackTrace();
}
}
}
private static boolean runMainApp(ClassLoader loader) {
ln("runMainApp() with loader: " + loader);
if (loader == null) loader = Runner.class.getClassLoader();
//MyClassLoader ucl = ((MyClassLoader)loader);
try {
//Class.forName("stitch.view.StitchFrame", true, loader);
Class c = loader.loadClass("stitch.view.Run");
c.newInstance();
}
catch (Exception ex) {
ex.printStackTrace();
return false;
}
return true;
}
}