Applet Loader Demo : Applet Loader « Development Class « Java

1. Java
2. Development Class
3. Applet Loader

Applet Loader Demo

 
import java.applet.Applet;
import java.io.IOException;
import java.io.InputStream;
import java.net.MalformedURLException;
import java.net.URL;
import java.net.URLConnection;
import java.util.Hashtable;

import javax.swing.JFrame;

public class MainClass {

  public static void main(String args[]) {
    String name = "http://urlWithClassName";
    try {
      if (!name.endsWith(".class")) {
        System.err.println("That doesn't look like a byte code file!");
        return;
      }
      URL u = new URL(name);
      URLClassLoader ucl = new URLClassLoader(u);

      // parse out the name of the class from the URL
      String s = u.getFile();
      String classname = s.substring(s.lastIndexOf('/'), s.lastIndexOf(".class"));
      Class AppletClass = ucl.loadClass(classname, true);
      Applet apl = (Applet) AppletClass.newInstance();
      JFrame f = new JFrame();
      f.setSize(200, 200);
      f.add("Center", apl);
      apl.init();
      apl.start();
      f.setVisible(true);
    } catch (Exception e) {
      System.err.println(e);
    }
  }
}

class URLClassLoader extends ClassLoader {
  Hashtable cache = new Hashtable();
  URL url;

  public URLClassLoader(URL u) {
    this.url = u;
  }

  public synchronized Class loadClass(String name, boolean resolve) throws ClassNotFoundException {
    Class cls = (Class) cache.get(name);
    if (cls == null) {
      try {
        cls = findSystemClass(name);
      } catch (ClassNotFoundException e) {
      }
    }
    if (cls == null) {
      byte classData[] = loadClassData(name);
      cls = defineClass(classData, 0, classData.length);
      cache.put(name, cls);
    }
    if (resolve) {
      resolveClass(cls);
    }
    return cls;
  }
  private byte[] loadClassData(String name) throws ClassNotFoundException {
    byte[] buffer;
    InputStream theClassInputStream = null;
    int bufferLength = 128;
    try {
      URL classURL = new URL(url, name + ".class");
      URLConnection uc = classURL.openConnection();
      uc.setAllowUserInteraction(false);

      try {
        theClassInputStream = uc.getInputStream();
      } catch (NullPointerException e) {
        System.err.println(e);
        throw new ClassNotFoundException(name + " input stream problem");
      }
      int contentLength = uc.getContentLength();

      // A lot of web servers don't send content-lengths
      // for .class files
      if (contentLength == -1) {
        buffer = new byte[bufferLength * 16];
      } else {
        buffer = new byte[contentLength];
      }

      int bytesRead = 0;
      int offset = 0;

      while (bytesRead >= 0) {
        bytesRead = theClassInputStream.read(buffer, offset, bufferLength);
        if (bytesRead == -1)
          break;
        offset += bytesRead;
        if (contentLength == -1 && offset == buffer.length) { // grow the array
          byte temp[] = new byte[offset * 2];
          System.arraycopy(buffer, 0, temp, 0, offset);
          buffer = temp;
        } else if (offset > buffer.length) {
          throw new ClassNotFoundException(name + " error reading data into the array");
        }
      }

      if (offset < buffer.length) { // shrink the array
        byte temp[] = new byte[offset];
        System.arraycopy(buffer, 0, temp, 0, offset);
        buffer = temp;
      }

      // Make sure all the bytes were received
      if (contentLength != -1 && offset != contentLength) {
        throw new ClassNotFoundException("Only " + offset + " bytes received for " + name
            + "\n Expected " + contentLength + " bytes");
      }
    } catch (Exception e) {
      throw new ClassNotFoundException(name + " " + e);
    } finally {
      try {
        if (theClassInputStream != null)
          theClassInputStream.close();
      } catch (IOException e) {
      }
    }
    return buffer;
  }
}

           
         
  

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