MultipleLoaderClassResolver.java

package com.gh.mygreen.xlsmapper.xml;

import java.util.Collection;
import java.util.HashSet;
import java.util.Iterator;
import java.util.Map;

import ognl.ClassResolver;

/**
 * ClassResolver loading from multiple ClassLoader in Ognl.
 *
 * @author Mitsuyoshi Hasegawa
 */
public class MultipleLoaderClassResolver implements ClassResolver {

    /**
     * Loads class from multiple ClassLoader.
     *
     * If this method can not load target class,
     * it tries to add package java.lang(default package)
     *  and load target class.
     * Still, if it can not the class, throws ClassNotFoundException.
     * (behavior is put together on DefaultClassResolver.)
     *
     * @param className class name --  that wants to load it.
     * @param loaderMap map -- that has VALUES ClassLoader (KEYS are arbitary).
     * @return loaded class from ClassLoader defined loaderMap.
     */
    @SuppressWarnings({"unchecked", "rawtypes"})
    public Class classForName(String className, Map loaderMap) throws ClassNotFoundException {
        Collection<ClassLoader> loaders = null;
        // add context-classloader
        loaders = new HashSet<ClassLoader>();
        loaders.add(Thread.currentThread().getContextClassLoader());
        if (loaderMap != null && !loaderMap.isEmpty()) {
            loaders.addAll(loaderMap.values());
        }
        Class clazz = null;
        ClassNotFoundException lastCause = null;
        for (Iterator<ClassLoader> it = loaders.iterator(); it.hasNext();) {
            ClassLoader loader = it.next();
            try {
                clazz = loader.loadClass(className);
                return clazz;
            } catch (ClassNotFoundException fqcnException) {
                lastCause = fqcnException;
                try {
                    if (className.indexOf('.') == -1) {
                        clazz = loader.loadClass("java.lang." + className);
                        return clazz;
                    }
                } catch (ClassNotFoundException defaultClassException) {
                    lastCause = defaultClassException;
                    // try next loader.
                }
            }
        }
        
        if(lastCause != null) {
            // can't load class at end.
            throw lastCause;
        }
        
        return clazz;
    }
}