Trying to load jar file dynamically

Question

I'm trying to load the jar file dynamically and making the new instance of an objet present in it.
mu source code -
import java.net.*;
import java.util.*;
import java.io.*;
import java.lang.reflect.Method;
class A
/** The class loader to use for loading JMeter classes. */
private static URLClassLoader loader;
     static {
          System.out.println("classpath : " + System.getProperty("java.class.path"));
URL[] urls = new URL[1];
StringBuffer classpath = new StringBuffer();
File f = new File("E:\\try\\lib\\dom4j.jar");
          String s = f.getPath();
try
               urls[0] = new URL("file", "", s);
          catch (MalformedURLException e)
               e.printStackTrace();
System.setProperty(
"java.class.path",
System.getProperty("java.class.path") + System.getProperty("path.separator") + s);
loader = new URLClassLoader(urls);
* Prevent instantiation.
private A()
* The main program which actually runs JMeter.
* @param args the command line arguments
public static void main(String[] args) throws Exception
          System.out.println("java,class.path : " + System.getProperty("java.class.path"));
Thread.currentThread().setContextClassLoader(loader);
          System.out.println("loader : " + loader);
          System.out.println("java.class.path : " + System.getProperty("java.class.path"));
          System.out.println("classpath : " + System.getenv("classpath"));
try
Class B = loader.loadClass("B");
Object instance = B.newInstance();
Method startup =
B.getMethod("print");
startup.invoke(instance);
catch (Exception e)
e.printStackTrace();
import org.dom4j.*;
import org.dom4j.dom.*;
import java.lang.reflect.*;
class B
     public void print () throws Exception
          //Element e = DocumentHelper.createElement("hello");     
          //e.addText("sachin");     
          //System.out.println(e.asXML());
ClassLoader loader = Thread.currentThread().getContextClassLoader();
          System.out.println("loader : " + loader);
Class c = loader.loadClass("org.dom4j.dom.DOMElement");
          //Class c = Class.forName("org.dom4j.dom.DOMElement");
          Constructor con = c.getConstructor(new String().getClass());
          DOMElement el = (DOMElement)con.newInstance(new String("asd"));
          //DOMElement dm = new DOMElement("ADD");
          System.out.println(el);
the class org.dom4j.dom.DOMElement is present in the jar file .
basically i'm getting an exception, given below--
java.lang.reflect.InvocationTargetException
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorI
java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodA
sorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:585)
at A.main(A.java:59)
Caused by: java.lang.NoClassDefFoundError: org/dom4j/dom/DOMElement
at B.print(B.java:18)
... 5 more
thanks alot..
Regards,
Sachin

Answer 1

Alright let me tell you guys what I am doing. I am using reflection to load the class from a jar file. Then, I am accessing a method defined in the class.
This piece of code will load and start the class;
Class c = loadClass(name);
System.out.println("name:" + name);
System.out.println("c:" + c);
Method m = c.getMethod("ServiceStarted", new Class[0]);
d1 = c.newInstance();
System.out.println("d1:" + d1);
m.setAccessible(true);
try {
m.invoke(d1, new Object[0] );
} catch (IllegalAccessException e) {
This piece of code will invoke a preloaded class;
String s = d1.getClass().getName();
Class c = Class.forName(s);
System.out.println(c);
Object ret = null;
Method m = c.getMethod("Hello", new Class[] { String.class });
Object d = c.newInstance();
m.setAccessible(true);
try {
ret = m.invoke(d, new Object[] { smsg });
} catch (IllegalAccessException e) {
and I have define d1 as;
private static Object d1 = new Object();
Any ideas why I am getting the exception.
Thanks,
MS