import java.util.*;
import java.io.*;
import java.net.*;


public class URLClassLoader extends ClassLoader {

  Hashtable cache = new Hashtable();
  URL theURL;

  public URLClassLoader(URL u) {

    // convert to a directory URL
    String file = u.getFile();
    int i = file.lastIndexOf('/');
    if ((i > 0) && (i < file.length()-1)) {
      try {
        u = new URL(u, file.substring(0, i+1));
      } 
      catch (MalformedURLException e) {
      }

    }

    theURL = u;

  }

  public URL getURL() {
    return theURL;
  }
  
  private Class downloadClass(String name) throws IOException {

    if (!name.toLowerCase().endsWith(".class")) name += ".class";
    URL u = new URL(theURL, name);

    InputStream is = null;
    try {
      try {
        URLConnection uc = u.openConnection();
        uc.setAllowUserInteraction(false);
        is = uc.getInputStream();
        int cl = uc.getContentLength();
        int buffersize;

        // Many servers don't return content length headers
        // If so, we'll guess that 2048 is long enough
        // and expand the array as we need to.
        if (cl <= 0) buffersize = 2048;
        else buffersize = cl;
        byte dotclass[] = new byte[buffersize];

        int totalRead = 0;    
        int bytesRead = 0;
        while ((bytesRead = is.read(dotclass, totalRead, dotclass.length - totalRead)) >= 0) {
          totalRead += bytesRead;
          if (totalRead == dotclass.length) {
            if (cl < 0) {
              // We don't know the content-length so we
              // keep reading until there aren't any bytes left
              byte temp[] = new byte[2*totalRead];
              System.arraycopy(dotclass, 0, temp, 0, totalRead);
              dotclass = temp;
            } 
            else {
              break;
            }
          }  
        }
        return defineClass(dotclass, 0, totalRead);
      } 
      finally {
        if (is != null) is.close();
      }
    } 
    catch (IOException e) {
      throw e;
    } 
    catch (Throwable t) {
      throw new IOException(u + " did not load");
    }

  }

  public Class loadClass(String name) throws ClassNotFoundException {

    return loadClass(name, true);

  }


  public Class loadClass(String name, boolean resolve) throws ClassNotFoundException {

     Class c = null;

     // try to get it from the cache;
     c = (Class) cache.get(name);
     if (c == null) {  // not in the cache
       try {
         return findSystemClass(name);
       }  
       catch (Throwable t) {
       }
      
       // not a system class
       try {
         c = downloadClass(name);
       }
       catch(IOException e) {
         // download failed
       }
    }

    if (c == null) {
      throw new ClassNotFoundException(name);
    }

    if (resolve) {
      resolveClass(c);
    }
   
    cache.put(name, c);

    return c;

  }
 
}