resourceutils.java

一个关于Spring框架的示例应用程序,简单使用,可以参考.

/*
 * Copyright 2002-2004 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.util;

import java.io.File;
import java.io.FileNotFoundException;
import java.net.MalformedURLException;
import java.net.URL;
import java.net.URLDecoder;

/**
 * Utility methods for resolving resource locations to files in the
 * file system. Mainly for internal use within the framework.
 *
 * <p>Consider using Spring's Resource abstraction in the core package
 * for handling all kinds of file resources in a uniform manner.
 * ResourceLoader's <code>getLocation</code> can resolve any location to a
 * Resource object, which in turn allows to get a <code>java.io.File</code>
 * in the file system through its <code>getFile</code> method.
 *
 * <p>The main reason for these utility methods for resource location
 * handling is to support Log4jConfigurer, which must be able to resolve
 * resource locations <i>before the logging system has been initialized</i>.
 * Spring' Resource abstraction in the core package, on the other hand,
 * already expects the logging system to be available.
 *
 * @author Juergen Hoeller
 * @since 1.1.5
 * @see org.springframework.core.io.Resource
 * @see org.springframework.core.io.ClassPathResource
 * @see org.springframework.core.io.FileSystemResource
 * @see org.springframework.core.io.UrlResource
 * @see org.springframework.core.io.ResourceLoader
 */
public abstract class ResourceUtils {

	/** Pseudo URL prefix for loading from the class path: "classpath:" */
	public static final String CLASSPATH_URL_PREFIX = "classpath:";

	/** URL protocol for a file in the file system: "file" */
	public static final String URL_PROTOCOL_FILE = "file";


	/**
	 * Return whether the given resource location is a URL:
	 * either a special "classpath" pseudo URL or a standard URL.
	 * @see #CLASSPATH_URL_PREFIX
	 * @see java.net.URL
	 */
	public static boolean isUrl(String resourceLocation) {
		if (resourceLocation.startsWith(CLASSPATH_URL_PREFIX)) {
			return true;
		}
		try {
			new URL(resourceLocation);
			return true;
		}
		catch (MalformedURLException ex) {
			return false;
		}
	}

	/**
	 * Resolve the given resource location to a <code>java.io.File</code>,
	 * i.e. to a file in the file system.
	 * <p>Does not check whether the file actually exists; simply returns
	 * the File that the given location would correspond to.
	 * @param resourceLocation the resource location to resolve: either a
	 * "classpath:" pseudo URL, a "file:" URL, or a plain file path
	 * @return a corresponding File object
	 * @throws FileNotFoundException if the resource cannot be resolved to
	 * a file in the file system
	 */
	public static URL getURL(String resourceLocation) throws FileNotFoundException {
		if (resourceLocation.startsWith(CLASSPATH_URL_PREFIX)) {
			String path = resourceLocation.substring(CLASSPATH_URL_PREFIX.length());
			String description = "class path resource [" + path + "]";
			URL url = Thread.currentThread().getContextClassLoader().getResource(path);
			if (url == null) {
				throw new FileNotFoundException(
						description + " cannot be resolved to URL because it does not exist");
			}
			return url;
		}
		try {
			// try URL
			return new URL(resourceLocation);
		}
		catch (MalformedURLException ex) {
			// no URL -> treat as file path
			try {
				return new URL("file:" + resourceLocation);
			}
			catch (MalformedURLException ex2) {
				throw new FileNotFoundException("Resource location [" + resourceLocation +
						"] is neither a URL not a well-formed file path");
			}
		}
	}

	/**
	 * Resolve the given resource location to a <code>java.io.File</code>,
	 * i.e. to a file in the file system.
	 * <p>Does not check whether the fil actually exists; simply returns
	 * the File that the given location would correspond to.
	 * @param resourceLocation the resource location to resolve: either a
	 * "classpath:" pseudo URL, a "file:" URL, or a plain file path
	 * @return a corresponding File object
	 * @throws FileNotFoundException if the resource cannot be resolved to
	 * a file in the file system
	 */
	public static File getFile(String resourceLocation) throws FileNotFoundException {
		if (resourceLocation.startsWith(CLASSPATH_URL_PREFIX)) {
			String path = resourceLocation.substring(CLASSPATH_URL_PREFIX.length());
			String description = "class path resource [" + path + "]";
			URL url = Thread.currentThread().getContextClassLoader().getResource(path);
			if (url == null) {
				throw new FileNotFoundException(
						description + " cannot be resolved to absolute file path " +
						"because it does not reside in the file system");
			}
			return getFile(url, description);
		}
		try {
			// try URL
			return getFile(new URL(resourceLocation));
		}
		catch (MalformedURLException ex) {
			// no URL -> treat as file path
			return new File(resourceLocation);
		}
	}

	/**
	 * Resolve the given resource URL to a <code>java.io.File</code>,
	 * i.e. to a file in the file system.
	 * @param resourceUrl the resource URL to resolve
	 * @return a corresponding File object
	 * @throws FileNotFoundException if the URL cannot be resolved to
	 * a file in the file system
	 */
	public static File getFile(URL resourceUrl) throws FileNotFoundException {
		return getFile(resourceUrl, "URL");
	}

	/**
	 * Resolve the given resource URL to a <code>java.io.File</code>,
	 * i.e. to a file in the file system.
	 * @param resourceUrl the resource URL to resolve
	 * @param description a description of the original resource that
	 * the URL was created for (for example, a class path location)
	 * @return a corresponding File object
	 * @throws FileNotFoundException if the URL cannot be resolved to
	 * a file in the file system
	 */
	public static File getFile(URL resourceUrl, String description) throws FileNotFoundException {
		if (!URL_PROTOCOL_FILE.equals(resourceUrl.getProtocol())) {
			throw new FileNotFoundException(
					description + " cannot be resolved to absolute file path " +
					"because it does not reside in the file system: " + resourceUrl);
		}
		return new File(URLDecoder.decode(resourceUrl.getFile()));
	}

}