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package com.sun.appserv.server.util;
import com.sun.enterprise.server.PELaunch;
import java.net.URL;
import java.net.URLClassLoader;
import java.util.Collections;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Map;
import java.util.Set;
/**
* <code>ASURLClassLoader</code> represents a individual component
* in the <code>ASClassLoaderChain</code>.
*
* Since it is a subclass of <code>URLClassLoader</code> it can contain a
* search path of one or more URLs
*
* @author Harsha RA, Sivakumar Thyagarajan
*/
public class ASURLClassLoader extends URLClassLoader {
/** List of URLs that this classloader checks for a class */
private URL[] classLoaderList = new URL[]{};
/** Name of this classloader - primarily used in the string
representation of the classloader - for debugging */
private String nameOfCL = null;
/** The classloader chain this classloader is a component of */
private ClassLoader parentChain = null;
/** toString() representation of parent - to prevent recursion */
private String parentToString = null;
//A local cache for keeping track of all classes that were not found
//using this classloader
private Set<String> notFoundClasses =
Collections.synchronizedSet(new HashSet<String>());
//A local cache for keeping track of all classes that were loaded
//using this classloader
private java.util.Hashtable<String,Class> loadedClasses =
new java.util.Hashtable<String,Class>();
/*
public ASURLClassLoader(URL[] urls) {
super(urls); //Parent: System ClassLoader.
this.classLoaderList = urls;
}
*/
public ASURLClassLoader(URL[] urls, ClassLoader parent) {
//The parent of the classloader chain component
//is either the SystemClassLoader (if shared chain is null!)
//or the Shared Chain.
//super(urls, PELaunch.getSharedChain());
super(urls, PELaunch.getSharedChain()!=null ?PELaunch.getSharedChain()
: ClassLoader.getSystemClassLoader());
this.parentChain = parent;
if(this.parentChain instanceof ClassLoaderChain) {
//Computed earlier to prevent recursion in toString of this
//class
this.parentToString =
((ClassLoaderChain)this.parentChain).getName();
} else {
this.parentToString = this.parentChain.toString();
}
this.classLoaderList = urls;
}
public void setName(String n) {
this.nameOfCL = n;
}
public String getName() {
return this.nameOfCL;
}
/**
* The loading strategy is:
* - check self first and
* - then delegate to parent chain if one exists. This is done to prevent recursion
* while referring to the chain. One issue with this approach is that when class load
* requests come via this component classloader, it might override a duplicate class in
* a peer present earlier in the chain.
*/
@Override
public Class<?> loadClass(String name, boolean resolve)
throws ClassNotFoundException {
try {
//perf optimization
//check notFoundClasses cache first
if (notFoundClasses.contains(name)) {
throw new ClassNotFoundException(name);
}
Class cls = null;
//perf optimization
//check loadedClasses cache first
cls = loadedClasses.get(name);
if (cls != null) {
return cls;
}
//Hands over to URLClassLoader.loadClass. First attempt to delegate
//to parent and then check for the class in the
//<code>classLoaderList</code>.
cls = super.loadClass(name, resolve);
if (cls != null) {
loadedClasses.put(name, cls);
return cls;
}
//Class not in this chain component.
throw new ClassNotFoundException(name);
} catch(ClassNotFoundException e) {
//If the parent is a ClassLoaderChain, check in the ClassLoaderChain
//ignoring this classloader component instance. Failure to do this
//would result in an infinte recursive call.
if ((parentChain != null) &&
(parentChain instanceof ClassLoaderChain)) {
ClassLoaderChain chain = (ClassLoaderChain)parentChain;
//Ask parent chain to load class, skipping self
Class c = chain.loadClass(name,this);
//Resolve if required.
if (c != null) {
if(resolve) {
resolveClass(c);
}
loadedClasses.put(name, c);
return c;
}
}
//perf optimization
if (!(notFoundClasses.contains(name))) {
notFoundClasses.add(name);
}
throw e;
}
}
@Override
public String toString() {
String s = this.nameOfCL + " parentCL :: " +
this.parentToString + " URLs :: \n";
for(URL u:classLoaderList){
s += ", " + u;
}
s +="\n";
return s;
}
}
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