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Utility classes and methods developed for Brooklyn but not dependendent on Brooklyn or much else

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package brooklyn.util.javalang;

import java.net.URL;
import java.util.List;
import java.util.concurrent.CopyOnWriteArrayList;

/** looks for classes and resources in the classloaders added here
 * 
 * similar to XStream's CompositeClassLoader, but also supporting resources,
 * exposing more info, a few conveniences, and a nice toString */
public class AggregateClassLoader extends ClassLoader {

    private final List classLoaders = new CopyOnWriteArrayList();

    private AggregateClassLoader() {}
    
    /** creates default instance, with classloaders of Object and AggregateClassLoader */
    public static AggregateClassLoader newInstanceWithDefaultLoaders() {
        AggregateClassLoader cl = new AggregateClassLoader();
        cl.addFirst(AggregateClassLoader.class.getClassLoader()); // whichever classloader loaded this jar.
        cl.addFirst(Object.class.getClassLoader()); // bootstrap loader.
        return cl;
    }
    /** creates default instance, with no classloaders (assuming this instance will itself be nested,
     * or defaults will be added by caller) */
    public static AggregateClassLoader newInstanceWithNoLoaders() {
        return new AggregateClassLoader();
    }

    /** Add a loader to the first position in the search path. */
    public void addFirst(ClassLoader classLoader) {
        if (classLoader != null) classLoaders.add(0, classLoader);
    }
    /** Add a loader to the last position in the search path. */
    public void addLast(ClassLoader classLoader) {
        if (classLoader != null) classLoaders.add(classLoader);
    }
    /** Add a loader to the specific position in the search path. 
     * (It is callers responsibility to ensure that position is valid.) */
    public void add(int index, ClassLoader classLoader) {
        if (classLoader != null) classLoaders.add(index, classLoader);
    }
    
    /** Returns the _live_ (and modifiable) list of classloaders 
     * @return */ 
    public List getList() {
        return classLoaders;
    }

    @Override
    protected Class findClass(String name) throws ClassNotFoundException {
        for (ClassLoader classLoader: classLoaders) {
            try {
                return classLoader.loadClass(name);
            } catch (ClassNotFoundException notFound) {
                /* ignore (nice if there were a better way than throwing... */
            }
        }
        // last resort. see comment in XStream CompositeClassLoader
        ClassLoader contextClassLoader = Thread.currentThread().getContextClassLoader();
        if (contextClassLoader != null)
            return contextClassLoader.loadClass(name);
        throw new ClassNotFoundException(name);
    }

    @Override
    public String toString() {
        return "AggregateClassLoader"+classLoaders;
    }
    
    @Override
    public URL getResource(String name) {
        URL result = null;
        for (ClassLoader classLoader: classLoaders) {
            result = classLoader.getResource(name);
            if (result!=null) return result;
        }
        // last resort. see comment in XStream CompositeClassLoader
        ClassLoader contextClassLoader = Thread.currentThread().getContextClassLoader();
        if (contextClassLoader != null) 
            return contextClassLoader.getResource(name);
        return null;
    }

    // TODO lesser used items, such as getResources, getPackage, findLibrary

}