Spring Framework example source code file (ResourceOverridingShadowingClassLoader.java)

This example Spring Framework source code file (ResourceOverridingShadowingClassLoader.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Java - Spring Framework tags/keywords

classloader, empty_url_enumeration, empty_url_enumeration, enumeration, enumeration, io, map, net, network, override, override, resourceoverridingshadowingclassloader, shadowingclassloader, string, string, unsupportedoperationexception, url, util

The Spring Framework ResourceOverridingShadowingClassLoader.java source code

/*
 * Copyright 2002-2006 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.instrument.classloading;

import java.io.IOException;
import java.io.InputStream;
import java.net.URL;
import java.util.Enumeration;
import java.util.HashMap;
import java.util.Map;

import org.springframework.util.Assert;

/**
 * Subclass of ShadowingClassLoader that overrides attempts to
 * locate certain files.
 *
 * @author Rod Johnson
 * @author Adrian Colyer
 * @since 2.0
 */
public class ResourceOverridingShadowingClassLoader extends ShadowingClassLoader {
	
	private static final Enumeration<URL> EMPTY_URL_ENUMERATION = new Enumeration() {
		public boolean hasMoreElements() {
			return false;
		}
		public URL nextElement() {
			throw new UnsupportedOperationException("Should not be called. I am empty.");
		}
	};
	

	/**
	 * Key is asked for value: value is actual value
	 */
	private Map<String, String> overrides = new HashMap();


	/**
	 * Create a new ResourceOverridingShadowingClassLoader,
	 * decorating the given ClassLoader.
	 * @param enclosingClassLoader the ClassLoader to decorate
	 */
	public ResourceOverridingShadowingClassLoader(ClassLoader enclosingClassLoader) {
		super(enclosingClassLoader);
	}
	

	/**
	 * Return the resource (if any) at the new path
	 * on an attempt to locate a resource at the old path.
	 * @param oldPath the path requested
	 * @param newPath the actual path to be looked up
	 */
	public void override(String oldPath, String newPath) {
		this.overrides.put(oldPath, newPath);
	}
	
	/**
	 * Ensure that a resource with the given path is not found.
	 * @param oldPath the path of the resource to hide even if
	 * it exists in the parent ClassLoader
	 */
	public void suppress(String oldPath) {
		this.overrides.put(oldPath, null);
	}

	/**
	 * Copy all overrides from the given ClassLoader.
	 * @param other the other ClassLoader to copy from
	 */
	public void copyOverrides(ResourceOverridingShadowingClassLoader other) {
		Assert.notNull(other, "Other ClassLoader must not be null");
		this.overrides.putAll(other.overrides);
	}


	@Override
	public URL getResource(String requestedPath) {
		if (this.overrides.containsKey(requestedPath)) {
			String overriddenPath = this.overrides.get(requestedPath);
			return (overriddenPath != null ? super.getResource(overriddenPath) : null);
		}
		else {
			return super.getResource(requestedPath);
		}
	}

	@Override
	public InputStream getResourceAsStream(String requestedPath) {
		if (this.overrides.containsKey(requestedPath)) {
			String overriddenPath = this.overrides.get(requestedPath);
			return (overriddenPath != null ? super.getResourceAsStream(overriddenPath) : null);
		}
		else {
			return super.getResourceAsStream(requestedPath);
		}
	}
	
	@Override
	public Enumeration<URL> getResources(String requestedPath) throws IOException {
		if (this.overrides.containsKey(requestedPath)) {
			String overriddenLocation = this.overrides.get(requestedPath);
			return (overriddenLocation != null ?
					super.getResources(overriddenLocation) : EMPTY_URL_ENUMERATION);
		}
		else {
			return super.getResources(requestedPath);
		}
	}

}