https://github.com/spring-projects/spring-framework: Spring Core (Spring IO)
  • Juergen Hoeller 
/*
 * Copyright 2002-2018 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.net.HttpURLConnection;
import java.net.URI;
import java.net.URL;
import java.net.URLConnection;
import java.nio.channels.FileChannel;
import java.nio.channels.ReadableByteChannel;
import java.nio.file.NoSuchFileException;
import java.nio.file.StandardOpenOption;

import org.springframework.util.ResourceUtils;


Abstract base class for resources which resolve URLs into File references, such as UrlResource or ClassPathResource. 
Detects the "file" protocol as well as the JBoss "vfs" protocol in URLs,
resolving file system references accordingly.

Author:Juergen Hoeller
Since:3.0
/**
 * Abstract base class for resources which resolve URLs into File references,
 * such as {@link UrlResource} or {@link ClassPathResource}.
 *
 * <p>Detects the "file" protocol as well as the JBoss "vfs" protocol in URLs,
 * resolving file system references accordingly.
 *
 * @author Juergen Hoeller
 * @since 3.0
 */
public abstract class AbstractFileResolvingResource extends AbstractResource {

	@Override
	public boolean exists() {
		try {
			URL url = getURL();
			if (ResourceUtils.isFileURL(url)) {
				// Proceed with file system resolution
				return getFile().exists();
			}
			else {
				// Try a URL connection content-length header
				URLConnection con = url.openConnection();
				customizeConnection(con);
				HttpURLConnection httpCon =
						(con instanceof HttpURLConnection ? (HttpURLConnection) con : null);
				if (httpCon != null) {
					int code = httpCon.getResponseCode();
					if (code == HttpURLConnection.HTTP_OK) {
						return true;
					}
					else if (code == HttpURLConnection.HTTP_NOT_FOUND) {
						return false;
					}
				}
				if (con.getContentLengthLong() > 0) {
					return true;
				}
				if (httpCon != null) {
					// No HTTP OK status, and no content-length header: give up
					httpCon.disconnect();
					return false;
				}
				else {
					// Fall back to stream existence: can we open the stream?
					getInputStream().close();
					return true;
				}
			}
		}
		catch (IOException ex) {
			return false;
		}
	}

	@Override
	public boolean isReadable() {
		try {
			URL url = getURL();
			if (ResourceUtils.isFileURL(url)) {
				// Proceed with file system resolution
				File file = getFile();
				return (file.canRead() && !file.isDirectory());
			}
			else {
				// Try InputStream resolution for jar resources
				URLConnection con = url.openConnection();
				customizeConnection(con);
				if (con instanceof HttpURLConnection) {
					HttpURLConnection httpCon = (HttpURLConnection) con;
					int code = httpCon.getResponseCode();
					if (code != HttpURLConnection.HTTP_OK) {
						httpCon.disconnect();
						return false;
					}
				}
				long contentLength = con.getContentLengthLong();
				if (contentLength > 0) {
					return true;
				}
				else if (contentLength == 0) {
					// Empty file or directory -> not considered readable...
					return false;
				}
				else {
					// Fall back to stream existence: can we open the stream?
					getInputStream().close();
					return true;
				}
			}
		}
		catch (IOException ex) {
			return false;
		}
	}

	@Override
	public boolean isFile() {
		try {
			URL url = getURL();
			if (url.getProtocol().startsWith(ResourceUtils.URL_PROTOCOL_VFS)) {
				return VfsResourceDelegate.getResource(url).isFile();
			}
			return ResourceUtils.URL_PROTOCOL_FILE.equals(url.getProtocol());
		}
		catch (IOException ex) {
			return false;
		}
	}

	
This implementation returns a File reference for the underlying class path
resource, provided that it refers to a file in the file system.

See Also:
  • getFile.getFile(URL, String)
/**
	 * This implementation returns a File reference for the underlying class path
	 * resource, provided that it refers to a file in the file system.
	 * @see org.springframework.util.ResourceUtils#getFile(java.net.URL, String)
	 */
	@Override
	public File getFile() throws IOException {
		URL url = getURL();
		if (url.getProtocol().startsWith(ResourceUtils.URL_PROTOCOL_VFS)) {
			return VfsResourceDelegate.getResource(url).getFile();
		}
		return ResourceUtils.getFile(url, getDescription());
	}

	
This implementation determines the underlying File
(or jar file, in case of a resource in a jar/zip).

/**
	 * This implementation determines the underlying File
	 * (or jar file, in case of a resource in a jar/zip).
	 */
	@Override
	protected File getFileForLastModifiedCheck() throws IOException {
		URL url = getURL();
		if (ResourceUtils.isJarURL(url)) {
			URL actualUrl = ResourceUtils.extractArchiveURL(url);
			if (actualUrl.getProtocol().startsWith(ResourceUtils.URL_PROTOCOL_VFS)) {
				return VfsResourceDelegate.getResource(actualUrl).getFile();
			}
			return ResourceUtils.getFile(actualUrl, "Jar URL");
		}
		else {
			return getFile();
		}
	}

	
This implementation returns a File reference for the given URI-identified
resource, provided that it refers to a file in the file system.

See Also:
Since:5.0
/**
	 * This implementation returns a File reference for the given URI-identified
	 * resource, provided that it refers to a file in the file system.
	 * @since 5.0
	 * @see #getFile(URI)
	 */
	protected boolean isFile(URI uri) {
		try {
			if (uri.getScheme().startsWith(ResourceUtils.URL_PROTOCOL_VFS)) {
				return VfsResourceDelegate.getResource(uri).isFile();
			}
			return ResourceUtils.URL_PROTOCOL_FILE.equals(uri.getScheme());
		}
		catch (IOException ex) {
			return false;
		}
	}

	
This implementation returns a File reference for the given URI-identified
resource, provided that it refers to a file in the file system.

See Also:
  • getFile.getFile(URI, String)
/**
	 * This implementation returns a File reference for the given URI-identified
	 * resource, provided that it refers to a file in the file system.
	 * @see org.springframework.util.ResourceUtils#getFile(java.net.URI, String)
	 */
	protected File getFile(URI uri) throws IOException {
		if (uri.getScheme().startsWith(ResourceUtils.URL_PROTOCOL_VFS)) {
			return VfsResourceDelegate.getResource(uri).getFile();
		}
		return ResourceUtils.getFile(uri, getDescription());
	}

	
This implementation returns a FileChannel for the given URI-identified
resource, provided that it refers to a file in the file system.

See Also:
Since:5.0
/**
	 * This implementation returns a FileChannel for the given URI-identified
	 * resource, provided that it refers to a file in the file system.
	 * @since 5.0
	 * @see #getFile()
	 */
	@Override
	public ReadableByteChannel readableChannel() throws IOException {
		try {
			// Try file system channel
			return FileChannel.open(getFile().toPath(), StandardOpenOption.READ);
		}
		catch (FileNotFoundException | NoSuchFileException ex) {
			// Fall back to InputStream adaptation in superclass
			return super.readableChannel();
		}
	}

	@Override
	public long contentLength() throws IOException {
		URL url = getURL();
		if (ResourceUtils.isFileURL(url)) {
			// Proceed with file system resolution
			File file = getFile();
			long length = file.length();
			if (length == 0L && !file.exists()) {
				throw new FileNotFoundException(getDescription() +
						" cannot be resolved in the file system for checking its content length");
			}
			return length;
		}
		else {
			// Try a URL connection content-length header
			URLConnection con = url.openConnection();
			customizeConnection(con);
			return con.getContentLengthLong();
		}
	}

	@Override
	public long lastModified() throws IOException {
		URL url = getURL();
		boolean fileCheck = false;
		if (ResourceUtils.isFileURL(url) || ResourceUtils.isJarURL(url)) {
			// Proceed with file system resolution
			fileCheck = true;
			try {
				File fileToCheck = getFileForLastModifiedCheck();
				long lastModified = fileToCheck.lastModified();
				if (lastModified > 0L || fileToCheck.exists()) {
					return lastModified;
				}
			}
			catch (FileNotFoundException ex) {
				// Defensively fall back to URL connection check instead
			}
		}
		// Try a URL connection last-modified header
		URLConnection con = url.openConnection();
		customizeConnection(con);
		long lastModified = con.getLastModified();
		if (fileCheck && lastModified == 0 && con.getContentLengthLong() <= 0) {
			throw new FileNotFoundException(getDescription() +
					" cannot be resolved in the file system for checking its last-modified timestamp");
		}
		return lastModified;
	}

	
Customize the given URLConnection, obtained in the course of an exists(), contentLength() or lastModified() call. 
Calls ResourceUtils.useCachesIfNecessary(URLConnection) and delegates to customizeConnection(HttpURLConnection) if possible. Can be overridden in subclasses. 
Params:
  • con – the URLConnection to customize
Throws:
/**
	 * Customize the given {@link URLConnection}, obtained in the course of an
	 * {@link #exists()}, {@link #contentLength()} or {@link #lastModified()} call.
	 * <p>Calls {@link ResourceUtils#useCachesIfNecessary(URLConnection)} and
	 * delegates to {@link #customizeConnection(HttpURLConnection)} if possible.
	 * Can be overridden in subclasses.
	 * @param con the URLConnection to customize
	 * @throws IOException if thrown from URLConnection methods
	 */
	protected void customizeConnection(URLConnection con) throws IOException {
		ResourceUtils.useCachesIfNecessary(con);
		if (con instanceof HttpURLConnection) {
			customizeConnection((HttpURLConnection) con);
		}
	}

	
Customize the given HttpURLConnection, obtained in the course of an exists(), contentLength() or lastModified() call. 
Sets request method "HEAD" by default. Can be overridden in subclasses.

Params:
  • con – the HttpURLConnection to customize
Throws:
  • IOException – if thrown from HttpURLConnection methods
/**
	 * Customize the given {@link HttpURLConnection}, obtained in the course of an
	 * {@link #exists()}, {@link #contentLength()} or {@link #lastModified()} call.
	 * <p>Sets request method "HEAD" by default. Can be overridden in subclasses.
	 * @param con the HttpURLConnection to customize
	 * @throws IOException if thrown from HttpURLConnection methods
	 */
	protected void customizeConnection(HttpURLConnection con) throws IOException {
		con.setRequestMethod("HEAD");
	}


	
Inner delegate class, avoiding a hard JBoss VFS API dependency at runtime.

/**
	 * Inner delegate class, avoiding a hard JBoss VFS API dependency at runtime.
	 */
	private static class VfsResourceDelegate {

		public static Resource getResource(URL url) throws IOException {
			return new VfsResource(VfsUtils.getRoot(url));
		}

		public static Resource getResource(URI uri) throws IOException {
			return new VfsResource(VfsUtils.getRoot(uri));
		}
	}

}