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package com.sun.appserv.server.util;
import java.util.ArrayList;
import java.util.Enumeration;
import java.util.Iterator;
import java.util.List;
import java.io.IOException;
import java.net.URL;
import java.security.SecureClassLoader;
/**
* Represents a classloader chain. A ClassLoader chain is a linked list of
* classloaders. All class requests is searched across the classloader chain in
* a horizontal manner. A classloader in this chain can either exist within
* the scope of this chain only or could be shared across multiple chains.
*
* @author Harsha RA, Sivakumar Thyagarajan
*/
public class ClassLoaderChain extends SecureClassLoader {
private List<ClassLoader> classLoaderList = new ArrayList<ClassLoader>();
private ClassLoader parentCL = null;
private String nameOfCL;
public ClassLoaderChain(){
super();
}
public ClassLoaderChain(ClassLoader parent){
super(parent);
this.parentCL = parent;
}
public void setName(String n) {
this.nameOfCL = n;
}
public String getName() {
return this.nameOfCL;
}
public void addToList(ClassLoader cl) {
this.classLoaderList.add(cl);
}
/**
* Mechanism to remove a classloader from a chain. This is especially
* useful in cases like uninstall-addon where a classloader has to be
* removed from a ClassLoaderChain dynamically at runtime
*/
public void removeFromList(ClassLoader cl) {
this.classLoaderList.remove(cl);
}
protected Class<?> findClass(String name) throws ClassNotFoundException {
throw new ClassNotFoundException(name);
}
/**
* Special loadClass method that attempts to a load a class in the chain,
* but skips the classLoader mentioned as "toSkip" to prevent infinite
* recursion, while going through the chain.
* @param name The binary name of the class
* @param toSkip ClassLoader component in the chain to skip while attempting
* to load a class.
* @return The resulting <code>Class</code> object
* @throws ClassNotFoundException If the class was not found in the other
* components of the chain.
*/
protected Class loadClass(String name, ClassLoader toSkip)
throws ClassNotFoundException {
//Iterate through all components in the chain.
for (Iterator<ClassLoader> iter = classLoaderList.iterator();
iter.hasNext();) {
ClassLoader element = iter.next();
if(element.equals(toSkip)) {
continue;
}
Class clz = null;
try {
//Attempt to load the class from a component in the chain.
clz = element.loadClass(name);
if (clz != null) {
return clz;
}
} catch (ClassNotFoundException e) {
//Ignore if a component in the chain fails to load the class.
//e.printStackTrace();
}
}
//All components in the chain failed to find the class.
throw new ClassNotFoundException(name);
}
/**
* Loads the class with the specified binary name.
* The traditional loadClass has been overridden to check if component
* classloaders in the chain could find the class.
*/
@Override
public Class<?> loadClass(String className,boolean resolve)
throws ClassNotFoundException {
//System.out.println(className + " attempted in Chain" + name );
Class c = findLoadedClass(className);
if( c != null ) {
return c;
}
//XXX: What happens if parentCL is a chain. - now we have addonchains as the parent
//of AS chain
// if( parentCL instanceof ClassLoaderChain ) {
// //warning message
// throw new RuntimeException("ClassLoader " + this.toString()
// + " parent is a chain " + parentCL.toString() );
// }
if (parentCL != null) {
try {
//Delegate to parent of chain first.!
c = parentCL.loadClass(className);
if (c != null) {
if (resolve) {
resolveClass(c);
}
}
} catch(ClassNotFoundException e) {
//ignore
}
if(c != null) {
//System.out.println("parent of " + this + "loaded " + className);
return c;
}
}
//Traverse through all classloaders in the chain to find class
for (ClassLoader element : classLoaderList) {
if(element == null)
continue;
Class clz = null;
try {
clz = element.loadClass(className);
if (clz != null) {
if(resolve) {
resolveClass(clz);
}
return clz;
}
//System.out.println(className + "was loaded by"+clz.getClassLoader());
} catch (ClassNotFoundException e) {
//e.printStackTrace();
}
}
//All components in the chain failed to find the class.
throw new ClassNotFoundException(className);
}
@Override
protected URL findResource(String name) {
for(ClassLoader cl:classLoaderList) {
URL res = cl.getResource(name);
if (res != null) return res;
}
return null;
}
@Override
protected Enumeration<URL> findResources(String name) throws IOException {
for(ClassLoader cl:classLoaderList) {
Enumeration<URL> res = cl.getResources(name);
List<URL> al = new ArrayList<URL>();
while(res.hasMoreElements()) {
al.add(res.nextElement());
}
if (al.size() != 0) {
return ((new java.util.Vector<URL>(al)).elements());
}
}
return ((new java.util.Vector<URL>()).elements());
}
@Override
public String toString() {
String s = this.nameOfCL + " parentCL :: " + this.parentCL +
" constituent CLs :: \n";
for(ClassLoader cl:this.classLoaderList) {
String nameofCL1 = null;
if (cl instanceof ASURLClassLoader) {
//As of now limiting this to just get the name.
nameofCL1 = ((ASURLClassLoader)cl).getName();
} else if (cl instanceof ClassLoaderChain) {
nameofCL1 = ((ClassLoaderChain)cl).getName();
}
s += " :: " + nameofCL1;
}
s += "\n";
return s;
}
}
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