// caches the class into a Hashtable
     classList.put(className, c);
    }

Listing 2.
try {
     c = findSystemClass(name);
     System.out.println("Resolved " + name + " locally");
    }

 // If Class is Not Local, Attempt to Resolved it From Downloaded Classes
catch (ClassNotFoundException e) {
       System.out.println("Resolving Class: " + name);
       classRequested = (Class) classList.get(name);

       if (classRequested == null) {
      System.out.println("Resolving " + name + " remotely");

      // If a Class has not been resolved previously then
      // attempt to load it from the last Web site that was
      // accessed.
                   loadClassName( name );
      c = ourClass;
   }
             }
             return c;

Listing 3.
public void loadClassName(String name) {
                 String URLlocation;
      try {
      URLlocation = new String("http://" + serv + dir + "/" + name + ".class");
      registerJavaClass(URLlocation);
                }
               catch (Exception e) {
     e.printStackTrace();
                }
             }

Listing 4.
Object obj = c.newInstance();
…

 // set the parameters for the static main method
 Class array1[] = {Class.forName("[Ljava.lang.String;")};

 // gets the static main method
 m1 = c.getMethod("main", array1);

 // invoke the static main method
 m1.invoke(obj, object_array);
 

Listing 5: urlclassloader.java
import java.net.*;
import java.io.*;
import java.util.*;

class URLClassLoader extends ClassLoader {

Class  ourClass=null;
Hashtable classList=null;
int  vector_counter;
String  directory=null;
String  server=null;
String  className=null;
String  UnresolvedURL=null;
String  temporaryURL=null;
boolean  flagClass;
static int counter1;

 public URLClassLoader() {

   super();

   classList = new Hashtable();
 }

 public void registerJavaClass(String URLlocation) throws IOException {

    String  filename=null;
    int  slash_index=0;
    InputStream  input=null;
    URL   u=null;
    DataInputStream data=null;

    try {
  u = new URL(URLlocation);
  temporaryURL = new String(URLlocation);

  filename = new String(u.getFile());
  slash_index = filename.lastIndexOf("/");
  className =
    new String(filename.substring(slash_index+1,
                       filename.length() - 6));

  directory =
   new String(filename.substring(0,
                                 slash_index));

  server = new String(u.getHost());

  input = u.openStream();

  data = new DataInputStream(input);

  byte classBytes[] =
    downloadByteCodesFromURL(data);

  data.close();
  input.close();
 
  input = null;
  u = null;
  System.gc();
 
  ourClass =
    createClassFromByteCodes(classBytes, true);

    } catch (Exception e) {

            if (input != null) {
                  input.close();
                  if (data != null) {
                      data.close();
                   }
            }
 
            u = null;
 
     UnresolvedURL = new String(URLlocation);

     ourClass = null;

     throw new IOException("Problems Defining " +
              "Network Class +++++++++++++++>");
    }
 }

 public byte[] downloadByteCodesFromURL(
                          DataInputStream in) {

    ByteArrayOutputStream outStream =
                    new ByteArrayOutputStream();
 
    while (true) {
  try {
   outStream.write(in.readByte());
  }
  catch (IOException e) {
   break;
  }
    }
    return outStream.toByteArray();
 }

 public synchronized Class
 createClassFromByteCodes(byte[] array,
                          boolean resolve) {

    Class c = null;

           try {
  c = defineClass(className, array,
                  0, array.length);
     if (resolve) {
           resolveClass(c);
            classList.put(className, c);
                }
    }
    catch (ClassFormatError e) {
  e.printStackTrace();
    }

    return (c);
 }

 public synchronized Class loadClass(String name,
                               boolean resolve)
  throws ClassNotFoundException {
    Class c = null;
    Class classRequested;

    // Attempt to Load the Class Locally First
    try {
     c = findSystemClass(name);
     System.out.println("Resolved " + name +
                        " locally");
    }
    // If Class is Not Local, Attempt to
    // Resolve it From Downloaded Classes
           catch (ClassNotFoundException e) {
     System.out.println("Resolving Class: " +
                        name);

     classRequested =
             (Class) classList.get(name);

     if (classRequested == null) {
     System.out.println("Resolving " + name +
                        " remotely");

     // If a Class has not been resolved
     // previously then attempt to load it
     // from the last web site that was accessed.
     loadClassName( name );
     c = ourClass;
  }
    }

    return c;
 }

 public void loadClassName(String name) {
    String   URLlocation;

    try {
  URLlocation = new String("http://" + server
           + directory + "/" + name + ".class");
  registerJavaClass(URLlocation);
    } catch (Exception e) {
  e.printStackTrace();
    }
 }

 public Class getTheClass() {
    return (ourClass);
 }
}

Listing 6: trigger.java
import java.awt.*;
import java.net.*;
import java.io.*;
import java.lang.reflect.*;
import java.awt.event.*;
import java.util.*;
import URLClassLoader;

public class trigger extends Frame implements ActionListener{

 URLClassLoader  loader=null;
 TextField  tf = null;
 Button   bt = null;

 public trigger() {
  super("Trigger Application");

  setLayout(new BorderLayout());
  tf = new TextField();
  bt = new Button("Execute Java Application");
  bt.addActionListener(this);

  add("North",
    new Label("Enter URL for loading Java application"));
  add("Center", tf);
  add("South", bt);

  loader = new URLClassLoader();

  setSize(300, 100);
 }

 public void actionPerformed(ActionEvent evt) {
  String URLLocation = tf.getText();

  if (URLLocation != null) {
     executeApplication(URLLocation);
  }
 }

   public void executeApplication(
                         String URLlocation) {

  try {
     loader.registerJavaClass(URLlocation);

         Class c = loader.getTheClass();

     startJavaApplication(c, "New Application");
  }
  catch (IOException e) {
    System.out.println("Error loading URL Class");
  }
   }

   public void startJavaApplication(
                       Class c, String label) {

                try {

    Object obj = c.newInstance();

           String[] array = new String[2];
           array[0] = new String(label);
           Object object_array[] = {array};

           Method m1;

          // set the parameters for main method
           Class array1[] =
           {Class.forName("[Ljava.lang.String;")};

    // get the static main method
    m1 = c.getMethod("main", array1);

    // invoke the static main method
    m1.invoke(obj, object_array);

                } catch (NoSuchMethodException e) {
          e.printStackTrace();
      } catch (ClassNotFoundException e) {
         e.printStackTrace();
      } catch (InvocationTargetException e) {
         e.printStackTrace();
      } catch (IllegalArgumentException e) {
     e.printStackTrace();
         } catch (IllegalAccessException e) {
     e.printStackTrace();
         } catch (InstantiationException e) {
     e.printStackTrace();
  } catch (NullPointerException e) {
     e.printStackTrace();
  }
   }

 public static void main(String args[]) {
  trigger application = new trigger();
  application.show();
 }
}