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*/
package org.glassfish.internal.api;
import com.sun.enterprise.module.common_impl.CompositeEnumeration;
import java.util.List;
import java.util.ArrayList;
import java.util.Enumeration;
import java.util.Collections;
import java.net.URL;
import java.io.IOException;
/**
* This classloader has a list of classloaders called as delegates
* that it uses to find classes. All those delegates must have the
* same parent as this classloader in order to have a consistent class space.
* By consistent class space, I mean a class space where no two loaded class
* have same name. An inconsistent class space can lead to ClassCastException.
* This classloader does not define any class, classes are always loaded
* either by its parent or by one of the delegates.
*
* @author Sanjeeb.Sahoo@Sun.COM
*/
public class DelegatingClassLoader extends ClassLoader {
/*
* TODO(Sahoo):
* 1. I18N
* 2. Move to a more common package, as it has no dependency on kernel.
*/
/**
* findClass method of ClassLoader is usually a protected method.
* Calling loadClass on a ClassLoader is expenssive, as it searches
* the delegation hierarchy before searching in its private space.
* Hence we add this interface as an optimization.
*/
public interface ClassFinder {
/**
* @see ClassLoader#getParent()
*/
ClassLoader getParent();
/**
* @see ClassLoader#findClass(String)
*/
Class<?> findClass(String name) throws ClassNotFoundException;
/**
* @see ClassLoader#findLoadedClass(String)
*/
Class<?> findExistingClass(String name);
/**
* @see ClassLoader#findResource(String)
*/
URL findResource(String name);
/**
* @see ClassLoader#findResources(String)
*/
Enumeration<URL> findResources(String name) throws IOException;
}
/**
* Name of this class loader. Used mostly for reporting purpose.
* No guarantee about its uniqueness.
*/
private String name;
private List<ClassFinder> delegates = new ArrayList<ClassFinder>();
/**
* @throws IllegalArgumentException when the delegate does not have same parent
* as this classloader.
*/
public DelegatingClassLoader(ClassLoader parent, List<ClassFinder> delegates)
throws IllegalArgumentException{
super(parent);
for (ClassFinder d : delegates) {
checkDelegate(d);
}
this.delegates.addAll(delegates);
}
public DelegatingClassLoader(ClassLoader parent) {
super(parent);
}
/**
* Adds a ClassFinder to list of delegates. To have a consistent
* class space (by consistent class space, I mean a classpace where there
* does not exist two class with same name), this method does not allow
* a delegate to be added that has a different parent.
* @param d ClassFinder to add to the list of delegates
* @return true if the delegate is added, false otherwise.
* @throws IllegalStateException when this method is called after the
* classloader has been used to load any class.
* @throws IllegalArgumentException when the delegate does not have same parent
* as this classloader.
*/
public synchronized boolean addDelegate(ClassFinder d) throws
IllegalStateException, IllegalArgumentException {
checkDelegate(d);
if (delegates.contains(d)) {
return false;
}
return delegates.add(d);
}
/**
* @throws IllegalArgumentException when the delegate does not have same parent
* as this classloader.
*/
private void checkDelegate(ClassFinder d) throws IllegalArgumentException {
final ClassLoader dp = d.getParent();
final ClassLoader p = getParent();
if (dp != p) { // check for equals
if ((dp != null && !dp.equals(p)) || !p.equals(dp)) {
throw new IllegalArgumentException("Delegation hierarchy mismatch");
}
}
}
/**
* Removes a ClassFinder from list of delegates. This method must not be used
* once this classloader has beed used to load any class. If attempted to
* do so, this method throws IllegalStateException
* @param d ClassFinder to remove from the list of delegates
* @return true if the delegate was removed, false otherwise.
* @throws IllegalStateException when this method is called after the
* classloader has been used to load any class.
*/
public synchronized boolean removeDelegate(ClassFinder d) {
return delegates.remove(d);
}
@Override
public Class<?> findClass(String name) throws ClassNotFoundException {
for (ClassFinder d : delegates) {
try {
Class c = null;
synchronized(d){
c = d.findExistingClass(name);
if(c == null){
c = d.findClass(name);
}
}
return c;
} catch (ClassNotFoundException e) {
// Ignore, as we search next in list
}
}
throw new ClassNotFoundException(name);
}
@Override
protected URL findResource(String name) {
for (ClassFinder d : delegates) {
URL u = d.findResource(name);
if (u!=null) return u;
}
return null;
}
@Override
protected Enumeration<URL> findResources(String name) throws IOException {
List<Enumeration<URL>> enumerators = new ArrayList<Enumeration<URL>>();
for (ClassFinder delegate : delegates) {
Enumeration<URL> enumerator = delegate.findResources(name);
enumerators.add(enumerator);
}
return new CompositeEnumeration(enumerators);
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public List<ClassFinder> getDelegates() {
return Collections.unmodifiableList(delegates);
}
@Override
public String toString() {
if (name!=null) {
return name;
} else {
return super.toString();
}
}
}