dynamically loading a class file from a jar file

[Srinivas Ramgopal]

Hi all,

I wrote a java program to load a .class file from a jar file.
The .class file resides in a different namespace than that of this java program.

I am using Class.forName(fully qualified class name) which is throwing a java.lang.ClassNotFoundException exception during runtime.

Code is as follows:

 
JarFile jarFile = new JarFile("../lib/xyz.jar");
 
JarEntry entry = jarFile.getJarEntry("zz/xx/Foo.class");
 
InputStream input = jarFile.getInputStream(entry);
 
InputStreamReader isr = new InputStreamReader(input);
BufferedReader reader = new BufferedReader(isr);
String className = entry.getName();
Class clazz= Class.forName("className");  
clazz.newInstance();
  

Any input is highly appreciated.

Thanks in advance.

[Freddy Wong]

I don't think that's how to dynamically load a JAR. Try to use URLClassLoader.

    
File jarFile = new File("/home/freddy/jars/HelloWorld.jar");
String className = "helloworld.Main";
try
{
    URL fileURL = jarFile.toURI().toURL();
    String jarURL = "jar:" + fileURL + "!/";
    URL urls [] = { new URL(jarURL) };
    URLClassLoader ucl = new URLClassLoader(urls);
    Messenger m = (Messenger) Class.forName(className, true,   ucl).newInstance();
    System.out.println(m.getMessage());
} 
catch (MalformedURLException ex)
{
    ex.printStackTrace();
}
catch (InstantiationException ex)
{
    ex.printStackTrace();
}
catch (IllegalAccessException ex)
{
    ex.printStackTrace();
}
catch (ClassNotFoundException ex)
{
    ex.printStackTrace();
}

[Bert Bates]

off to the intermediate forum