Problem with loading classes!!!

Question

I am loading classes using
// Open File
InputStream jarFile = new BufferedInputStream(new FileInputStream(
pluginPath));
// Get Manifest and properties
Attributes attrs = new JarInputStream(jarFile).getManifest().
getMainAttributes();
jarFile.close();
// Read Main Class
String mainClass = attrs.getValue("Protocol-Class");
// Load all classes from jar file without giving classpath
URL url = new URL("jar:file:" + pluginPath + "!/");
JarURLConnection jarConnection = (JarURLConnection) url.openConnection();
URL[] urls = new URL[] {
url};
ClassLoader classLoader = new URLClassLoader(urls);
// Create new instance of protocol
Protocol protocol = (Protocol) classLoader.loadClass(mainClass).
newInstance();
I am loading classes one by one say a order A, B, C. In my case class c extends class A. So I am loading class A first and later B and finally C. But I am getting exceptions when loading class C that Class A is unknown.The following exception is thrown
java.lang.NoClassDefFoundError: com/a/A at java.lang.ClassLoader.defineClass0(Native Method) at java.lang.ClassLoader.defineClass(ClassLoader.java:537)
Please give me a solution to make it run.

Answer 1

You create a new class loader for each class. The class loaders are independent, and so the class hierarchies they load are independent. Class A loader by classLoaderOne doesn't see class B loader by classLoaderTwo - they are loaded into their own sandboxes.
Either load everything with one class loader or create the class loaders in a hierarchy. To create a hierarchy use the class loader constructor that takes a parent class loader as a parameter. One class loader may be easier because then you don't need to worry about loading order.