Mega Code Archive
Applet Loader Demo
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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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