The most important point is to correctly set the parent class loader which is null here .
note: with windows custom urlClassLoader is necessary which is overrides the close method of the base class (due to a jvm bug{may be fixed in jdk7})
import static java.nio.file.StandardWatchEventKinds.ENTRY_CREATE;
import static java.nio.file.StandardWatchEventKinds.ENTRY_MODIFY;
import java.io.File;
import java.lang.reflect.Method;
import java.net.URL;
import java.net.URLClassLoader;
import java.nio.file.FileSystems;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.nio.file.WatchEvent;
import java.nio.file.WatchKey;
import java.nio.file.WatchService;
public class JarReloader {
public static void main(String[] args) {
Runnable r = new Runnable() {
@Override
public void run() {
while (true) {
reloadJarFile();
watchDirectory();
}
}
private void reloadJarFile() {
try {
System.out.println("Reloading the jar file !");
URLClassLoader cl = null;
File file = new File("/home/ssunel/jars/reload.jar");
String classToLoad = "com.freetime.enjoy.ReloadMe";
URL jarUrl = new URL("file:" + file.getAbsolutePath());
cl = new URLClassLoader(new URL[] {jarUrl}, null);
Class loadedClass = cl.loadClass(classToLoad);
Method method = loadedClass.getMethod("giveAMessage", new Class[] {});
Object reloadMe = loadedClass.getConstructor().newInstance();
method.invoke(reloadMe, null);
} catch (Exception e) {
e.printStackTrace();
}
}
private void watchDirectory() {
try {
Path dir = Paths.get("/home/ssunel/jars");
WatchService watchService = FileSystems.getDefault().newWatchService();
dir.register(watchService, ENTRY_CREATE, ENTRY_MODIFY);
WatchKey watchKey = watchService.take();
for (WatchEvent<?> event : watchKey.pollEvents()) {
WatchEvent<Path> ev = (WatchEvent<Path>) event;
Path name = ev.context();
Path child = dir.resolve(name);
System.out.format("%s: %s\n", event.kind().name(), child);
}
Thread.sleep(1000L);
} catch (Exception x) {
return;
}
}
};
startReloader(r);
}
private static void startReloader(Runnable r) {
try {
Thread reloader = new Thread(r);
reloader.start();
reloader.join();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
package com.freetime.enjoy;
public class ReloadMe {
private final static String someMessage = "HELLO WORLD AGAIN";
public static void giveAMessage (){
System.out.println(someMessage);
}
}
