package com.thoughtworks.xstream.core.util;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Iterator;
import java.util.List;
/**
* ClassLoader that is composed of other classloaders. Each loader will be used to try to load the particular class, until
* one of them succeeds. <b>Note:</b> The loaders will always be called in the REVERSE order they were added in.
*
* <p>The Composite class loader also has registered the classloader that loaded xstream.jar
* and (if available) the thread's context classloader.</p>
*
* <h1>Example</h1>
* <pre><code>CompositeClassLoader loader = new CompositeClassLoader();
* loader.add(MyClass.class.getClassLoader());
* loader.add(new AnotherClassLoader());
*
* loader.loadClass("com.blah.ChickenPlucker");
* </code></pre>
*
* <p>The above code will attempt to load a class from the following classloaders (in order):</p>
*
* <ul>
* <li>AnotherClassLoader (and all its parents)</li>
* <li>The classloader for MyClas (and all its parents)</li>
* <li>The thread's context classloader (and all its parents)</li>
* <li>The classloader for XStream (and all its parents)</li>
* </ul>
*
* @author Joe Walnes
* @since 1.0.3
*/
public class CompositeClassLoader extends ClassLoader {
private final List classLoaders = Collections.synchronizedList(new ArrayList());
public CompositeClassLoader() {
add(Object.class.getClassLoader()); // bootstrap loader.
add(getClass().getClassLoader()); // whichever classloader loaded this jar.
}
/**
* Add a loader to the n
* @param classLoader
*/
public void add(ClassLoader classLoader) {
if (classLoader != null) {
classLoaders.add(0, classLoader);
}
}
public Class loadClass(String name) throws ClassNotFoundException {
for (Iterator iterator = classLoaders.iterator(); iterator.hasNext();) {
ClassLoader classLoader = (ClassLoader) iterator.next();
try {
return classLoader.loadClass(name);
} catch (ClassNotFoundException notFound) {
// ok.. try another one
}
}
// One last try - the context class loader associated with the current thread. Often used in j2ee servers.
// Note: The contextClassLoader cannot be added to the classLoaders list up front as the thread that constructs
// XStream is potentially different to thread that uses it.
ClassLoader contextClassLoader = Thread.currentThread().getContextClassLoader();
if (contextClassLoader != null) {
return contextClassLoader.loadClass(name);
} else {
throw new ClassNotFoundException(name);
}
}
}
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