/*
    * Copyright 2002-2012 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.FileNotFoundException;
  import java.io.IOException;
  import java.io.InputStream;
  import java.net.URI;
  import java.net.URISyntaxException;
  import java.net.URL;
  
  import org.springframework.core.NestedIOException;
  import org.springframework.util.ResourceUtils;
  
  /**
   * Convenience base class for {@link Resource} implementations,
   * pre-implementing typical behavior.
   *
   * <p>The "exists" method will check whether a File or InputStream can
   * be opened; "isOpen" will always return false; "getURL" and "getFile"
   * throw an exception; and "toString" will return the description.
   *
   * @author Juergen Hoeller
   * @since 28.12.2003
   */
  public abstract class AbstractResource implements Resource {
  
  	/**
  	 * This implementation checks whether a File can be opened,
  	 * falling back to whether an InputStream can be opened.
  	 * This will cover both directories and content resources.
  	 */
  	public boolean exists() {
  		// Try file existence: can we find the file in the file system?
  		try {
  			return getFile().exists();
  		}
  		catch (IOException ex) {
  			// Fall back to stream existence: can we open the stream?
  			try {
  				InputStream is = getInputStream();
  				is.close();
  				return true;
  			}
  			catch (Throwable isEx) {
  				return false;
  			}
  		}
  	}
  
  	/**
  	 * This implementation always returns <code>true</code>.
  	 */
  	public boolean isReadable() {
  		return true;
  	}
  
  	/**
  	 * This implementation always returns <code>false</code>.
  	 */
  	public boolean isOpen() {
  		return false;
  	}
  
  	/**
  	 * This implementation throws a FileNotFoundException, assuming
  	 * that the resource cannot be resolved to a URL.
  	 */
  	public URL getURL() throws IOException {
  		throw new FileNotFoundException(getDescription() + " cannot be resolved to URL");
  	}
  
  	/**
  	 * This implementation builds a URI based on the URL returned
  	 * by {@link #getURL()}.
  	 */
  	public URI getURI() throws IOException {
  		URL url = getURL();
  		try {
  			return ResourceUtils.toURI(url);
  		}
  		catch (URISyntaxException ex) {
  			throw new NestedIOException("Invalid URI [" + url + "]", ex);
  		}
 	}
 
 	/**
 	 * This implementation throws a FileNotFoundException, assuming
 	 * that the resource cannot be resolved to an absolute file path.
 	 */
 	public File getFile() throws IOException {
 		throw new FileNotFoundException(getDescription() + " cannot be resolved to absolute file path");
 	}
 
 	/**
 	 * This implementation reads the entire InputStream to calculate the
 	 * content length. Subclasses will almost always be able to provide
 	 * a more optimal version of this, e.g. checking a File length.
 	 * @see #getInputStream()
 	 */
 	public long contentLength() throws IOException {
 		InputStream is = getInputStream();
 		try {
 			long size = 0;
 			byte[] buf = new byte[255];
 			int read;
 			while ((read = is.read(buf)) != -1) {
 				size += read;
 			}
 			return size;
 		}
 		finally {
 			try {
 				is.close();
 			}
 			catch (IOException ex) {
 			}
 		}
 	}
 
 	/**
 	 * This implementation checks the timestamp of the underlying File,
 	 * if available.
 	 * @see #getFileForLastModifiedCheck()
 	 */
 	public long lastModified() throws IOException {
 		long lastModified = getFileForLastModifiedCheck().lastModified();
 		if (lastModified == 0L) {
 			throw new FileNotFoundException(getDescription() +
 					" cannot be resolved in the file system for resolving its last-modified timestamp");
 		}
 		return lastModified;
 	}
 
 	/**
 	 * Determine the File to use for timestamp checking.
 	 * <p>The default implementation delegates to {@link #getFile()}.
 	 * @return the File to use for timestamp checking (never <code>null</code>)
 	 * @throws IOException if the resource cannot be resolved as absolute
 	 * file path, i.e. if the resource is not available in a file system
 	 */
 	protected File getFileForLastModifiedCheck() throws IOException {
 		return getFile();
 	}
 
 	/**
 	 * This implementation throws a FileNotFoundException, assuming
 	 * that relative resources cannot be created for this resource.
 	 */
 	public Resource createRelative(String relativePath) throws IOException {
 		throw new FileNotFoundException("Cannot create a relative resource for " + getDescription());
 	}
 
 	/**
 	 * This implementation always returns <code>null</code>,
 	 * assuming that this resource type does not have a filename.
 	 */
 	public String getFilename() {
 		return null;
 	}
 
 
 	/**
 	 * This implementation returns the description of this resource.
 	 * @see #getDescription()
 	 */
 	@Override
 	public String toString() {
 		return getDescription();
 	}
 
 	/**
 	 * This implementation compares description strings.
 	 * @see #getDescription()
 	 */
 	@Override
 	public boolean equals(Object obj) {
 		return (obj == this ||
 		    (obj instanceof Resource && ((Resource) obj).getDescription().equals(getDescription())));
 	}
 
 	/**
 	 * This implementation returns the description's hash code.
 	 * @see #getDescription()
 	 */
 	@Override
 	public int hashCode() {
 		return getDescription().hashCode();
 	}
 
 }