resource.java

Java/J2EE application framework based on [Expert One-on-One J2EE Design and Development] by Rod John

/*
 * 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.core.io;

import java.io.File;
import java.io.IOException;
import java.net.URL;

/**
 * Interface for a resource descriptor that abstracts from the actual
 * type of resource, like file or class path resource.
 *
 * <p>An InputStream can be opened for every resource if it exists in
 * physical form, but a URL or File handle can just be returned for
 * certain resources. The actual behavior is implementation-specific.
 *
 * @author Juergen Hoeller
 * @since 28.12.2003
 */
public interface Resource extends InputStreamSource {

	/**
	 * Return whether this resource actually exists in physical form.
	 */
	boolean exists();

	/**
	 * Return whether this resource represents a handle with an open
	 * stream. If true, the InputStream cannot be read multiple times,
	 * and must be read and closed to avoid resource leaks.
	 * <p>Will be false for all usual resource descriptors.
	 */
	boolean isOpen();

	/**
	 * Return a URL handle for this resource.
	 * @throws IOException if the resource cannot be resolved as URL,
	 * i.e. if the resource is not available as descriptor
	 */
	URL getURL() throws IOException;

	/**
	 * Return a File handle for this resource.
	 * @throws IOException if the resource cannot be resolved as absolute
	 * file path, i.e. if the resource is not available in a file system
	 */
	File getFile() throws IOException;

	/**
	 * Create a resource relative to this resource.
	 * @param relativePath the relative path (relative to this resource)
	 * @return the resource handle for the relative resource
	 * @throws IOException if the relative resource cannot be determined
	 */
	Resource createRelative(String relativePath) throws IOException;

	/**
	 * Return a filename for this resource, i.e. typically the last
	 * part of the path: for example, "myfile.txt".
	 */
	String getFilename();

	/**
	 * Return a description for this resource,
	 * to be used for error output when working with the resource.
	 * <p>Implementations are also encouraged to return this value
	 * from their toString method.
	 * @see java.lang.Object#toString
	 */
	String getDescription();

}