Classloader won't let me delete jar file!

Question

Hi-
I am writing a classloader that runs main from a class called MyMain. MyMain loads classes from a jar file called MattTable.jar. I need to be able to delete the jar file once the classes are loaded from it, or even just delete it at the end of the program. Either way, the classloader will not release it so I cannot delete the jar file until after my program finishes. I want to be able to delete it from with in my code after the method is invoked.
URL urls[] = new URL[] { new File(".").toURL() };
URLClassLoader loader = new URLClassLoader( urls );
Class c = loader.loadClass(mainClass);
Method m1 = c.getMethod("main", new Class[] { args.getClass() });
//main loads classes from an outside jar file
m1.invoke( null, new Object[] {args} );
//Here is where I want to delete the jar file
//I would even accept file.deleteOnExit() but this won't work either
If anyone can help me figure out how to delete this file, it would be a great help!
Thanks,
Matt

Answer 1

Hi,
I've created a small classloader for jar files which releases the handle every time a class is loaded. It might still need some optimization, but at least it works:import java.util.zip.*;
import java.util.*;
import java.io.*;
public class ZipClassLoader extends ClassLoader {
     private Hashtable classes = new Hashtable();
     private File f;
     public ZipClassLoader(String zipFileName) {
          this (new File(zipFileName));
     public ZipClassLoader(File zipFile) {
          f = zipFile;
     public Class loadClass(String className) throws ClassNotFoundException {
          return (loadClass(className, true));
     public synchronized Class loadClass(String className, boolean resolve) throws ClassNotFoundException {
          if (classes.containsKey(className)) return (Class)classes.get(className);
          ZipFile zipFile = null;
          BufferedInputStream bis = null;
          byte[] res = null;
          try {
               zipFile = new ZipFile(f);
               ZipEntry zipEntry = zipFile.getEntry(className.replace('.', '/')+".class");
               res = new byte[(int)zipEntry.getSize()];
               bis = new BufferedInputStream(zipFile.getInputStream(zipEntry));
               bis.read(res, 0, res.length);
          } catch (Exception ex) {
          } finally {
               if (bis!=null) {
                    try {
                         bis.close();
                    } catch (IOException ioex) {}
               if (zipFile!=null) {
                    try {
                         zipFile.close();
                    } catch (IOException ioex) {}
          if (res == null) return super.findSystemClass(className);
          Class clazz = defineClass(className, res, 0, res.length);
          if (clazz == null) throw new ClassFormatError();
          if (resolve) resolveClass(clazz);
          classes.put(className, clazz);
          return(clazz);
}This is the test program I've created. It loads a class from the Apache log4j jar file, and deletes the file when the class is loaded:import java.io.File;
public class Test {
     public static void main(String[] args) throws Exception {
          File f = new File("C:\\jartest\\log4j-1.2.6.jar");
          ZipClassLoader zl = new ZipClassLoader (f);
          Class c = zl.loadClass ("org.apache.log4j.ConsoleAppender", true);
          Object o = c.newInstance();
          System.out.println (o.getClass().getName());
          f.delete();
}