/*
 * Copyright 2002-2008 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.core.io;

import java.net.MalformedURLException;
import java.net.URL;

import org.springframework.util.Assert;
import org.springframework.util.ClassUtils;
import org.springframework.util.StringUtils;

/**
 * Default implementation of the {@link ResourceLoader} interface.
 * Used by {@link ResourceEditor}, and serves as base class for
 * {@link org.springframework.context.support.AbstractApplicationContext}.
 * Can also be used standalone.
 *
 * <p>Will return a {@link UrlResource} if the location value is a URL,
 * and a {@link ClassPathResource} if it is a non-URL path or a
 * "classpath:" pseudo-URL.
 *
 * @author Juergen Hoeller
 * @since 10.03.2004
 * @see FileSystemResourceLoader
 * @see org.springframework.context.support.ClassPathXmlApplicationContext
 */
public class DefaultResourceLoader implements ResourceLoader {

	private ClassLoader classLoader;


	/**
	 * Create a new DefaultResourceLoader.
	 * <p>ClassLoader access will happen using the thread context class loader
	 * at the time of this ResourceLoader's initialization.
	 * @see java.lang.Thread#getContextClassLoader()
	 */
	public DefaultResourceLoader() {
		this.classLoader = ClassUtils.getDefaultClassLoader();
	}

	/**
	 * Create a new DefaultResourceLoader.
	 * @param classLoader the ClassLoader to load class path resources with, or <code>null</code>
	 * for using the thread context class loader at the time of actual resource access
	 */
	public DefaultResourceLoader(ClassLoader classLoader) {
		this.classLoader = classLoader;
	}


	/**
	 * Specify the ClassLoader to load class path resources with, or <code>null</code>
	 * for using the thread context class loader at the time of actual resource access.
	 * <p>The default is that ClassLoader access will happen using the thread context
	 * class loader at the time of this ResourceLoader's initialization.
	 */
	public void setClassLoader(ClassLoader classLoader) {
		this.classLoader = classLoader;
	}

	/**
	 * Return the ClassLoader to load class path resources with,
	 * or <code>null</code> if using the thread context class loader on actual access
	 * (applying to the thread that constructs the ClassPathResource object).
	 * <p>Will get passed to ClassPathResource's constructor for all
	 * ClassPathResource objects created by this resource loader.
	 * @see ClassPathResource
	 */
	public ClassLoader getClassLoader() {
		return this.classLoader;
	}


	public Resource getResource(String location) {
		Assert.notNull(location, "Location must not be null");
		if (location.startsWith(CLASSPATH_URL_PREFIX)) {
			return new ClassPathResource(location.substring(CLASSPATH_URL_PREFIX.length()), getClassLoader());
		}
		else {
			try {
				// Try to parse the location as a URL...
				URL url = new URL(location);
				return new UrlResource(url);
			}
			catch (MalformedURLException ex) {
				// No URL -> resolve as resource path.
				return getResourceByPath(location);
			}
		}
	}

	/**
	 * Return a Resource handle for the resource at the given path.
	 * <p>The default implementation supports class path locations. This should
	 * be appropriate for standalone implementations but can be overridden,
	 * e.g. for implementations targeted at a Servlet container.
	 * @param path the path to the resource
	 * @return the corresponding Resource handle
	 * @see ClassPathResource
	 * @see org.springframework.context.support.FileSystemXmlApplicationContext#getResourceByPath
	 * @see org.springframework.web.context.support.XmlWebApplicationContext#getResourceByPath
	 */
	protected Resource getResourceByPath(String path) {
		return new ClassPathContextResource(path, getClassLoader());
	}


	/**
	 * ClassPathResource that explicitly expresses a context-relative path
	 * through implementing the ContextResource interface.
	 */
	private static class ClassPathContextResource extends ClassPathResource implements ContextResource {

		public ClassPathContextResource(String path, ClassLoader classLoader) {
			super(path, classLoader);
		}

		public String getPathWithinContext() {
			return getPath();
		}

		public Resource createRelative(String relativePath) {
			String pathToUse = StringUtils.applyRelativePath(getPath(), relativePath);
			return new ClassPathContextResource(pathToUse, getClassLoader());
		}
	}

}