DefaultResourceLoader.java

/*
 * Copyright 2002-2013 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.grails.io.support;

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

/**
 * Default implementation of the ResourceLoader interface.
 *
 * <p>Will return a UrlResource if the location value is a URL,
 * and a ClassPathResource if it is a non-URL path or a
 * "classpath:" pseudo-URL.
 *
 * @author Juergen Hoeller
 * @since 10.03.2004
 */
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() {
        classLoader = getDefaultClassLoader();
    }

    public static ClassLoader getDefaultClassLoader() {
        ClassLoader cl = null;
        try {
            cl = Thread.currentThread().getContextClassLoader();
        }
        catch (Throwable ex) {
            // Cannot access thread context ClassLoader - falling back to system class loader...
        }
        if (cl == null) {
            // No thread context class loader -> use class loader of this class.
            cl = DefaultResourceLoader.class.getClassLoader();
        }
        return cl;
    }

    /**
     * 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.
     */
    public ClassLoader getClassLoader() {
        return classLoader == null ? getDefaultClassLoader() : classLoader;
    }

    public Resource getResource(String location) {
        if (location.startsWith(CLASSPATH_URL_PREFIX)) {
            return new ClassPathResource(location.substring(CLASSPATH_URL_PREFIX.length()), getClassLoader());
        }

        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
     */
    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 {

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

        @SuppressWarnings("unused")
        public String getPathWithinContext() {
            return getPath();
        }

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