java 实现下载htttp文件的简便办法 FileUtils IOUtils

女爷i 2022-08-08 06:55 196阅读 0赞

其实很多时候，我们并不需要去重复造轮子，只需要借 就可以。但是前提就得你得知道谁家有轮子可借才行。这次就用到了 org.apache.common.io 家的轮子了。

具体实现：

public String downloadHttpUrl(String url, String dir) {
    		String fileName = "test.jpg";
    		try {
    			URL httpurl = new URL(url);
    			File f = new File(dir + fileName);
    			FileUtils.copyURLToFile(httpurl, f);
    		} catch (Exception e) {
    			e.printStackTrace();
    			return "";
    		}
    		return dir + fileName;
    	}

上文中用到的 FileUtils 来源于： org.apache.commons.io.FileUtils 。那么问题又来了 他是怎么实现的呢，接着往下看源码FileUtils.clsss

public static void copyURLToFile(URL source, File destination) throws IOException {
            InputStream input = source.openStream();
            try {
                FileOutputStream output = openOutputStream(destination);
                try {
                    IOUtils.copy(input, output);
                } finally {
                    IOUtils.closeQuietly(output);
                }
            } finally {
                IOUtils.closeQuietly(input);
            }
        }

继续： IOUtils.copy 具体干了哪些活呢

public static int copy(InputStream input, OutputStream output) throws IOException {
            long count = copyLarge(input, output);
            if (count > Integer.MAX_VALUE) {
                return -1;
            }
            return (int) count;
        }

copylarge

public static long copyLarge(InputStream input, OutputStream output)
                throws IOException {
            byte[] buffer = new byte[DEFAULT_BUFFER_SIZE];
            long count = 0;
            int n = 0;
            while (-1 != (n = input.read(buffer))) {
                output.write(buffer, 0, n);
                count += n;
            }
            return count;
        }

哦哦哦，原来如此，  无非也是 InputStream  到  OutputStream 的 过程。 现在反过来想想，如果没有借助此轮子，自己去造是不是思路也一样用到  InputStream   和  OutputStream    。 既然人家已经有了就要学会拿来用。

这样一来，通过一个下载 我们就学习了两个轮子  org.apache.commons.io.FileUtils   和  org.apache.commons.io.IOUtils .

引申学习：这里面封装好了很多我们平时经常用的方法，为日常编码带来很多方便。

/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements. See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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.apache.commons.io;
 
 import java.io.File;
 import java.io.FileFilter;
 import java.io.FileInputStream;
 import java.io.FileNotFoundException;
 import java.io.FileOutputStream;
 import java.io.IOException;
 import java.io.InputStream;
 import java.io.OutputStream;
 import java.net.URL;
 import java.util.Collection;
 import java.util.Date;
 import java.util.Iterator;
 import java.util.List;
 import java.util.zip.CRC32;
 import java.util.zip.CheckedInputStream;
 import java.util.zip.Checksum;
 
 import org.apache.commons.io.filefilter.DirectoryFileFilter;
 import org.apache.commons.io.filefilter.FalseFileFilter;
 import org.apache.commons.io.filefilter.FileFilterUtils;
 import org.apache.commons.io.filefilter.IOFileFilter;
 import org.apache.commons.io.filefilter.SuffixFileFilter;
 import org.apache.commons.io.filefilter.TrueFileFilter;
 import org.apache.commons.io.output.NullOutputStream;
 
 /**
 * General file manipulation utilities.
 * 
 * Facilities are provided in the following areas:
 * <ul>
 * <li>writing to a file
 * <li>reading from a file
 * <li>make a directory including parent directories
 * <li>copying files and directories
 * <li>deleting files and directories
 * <li>converting to and from a URL
 * <li>listing files and directories by filter and extension
 * <li>comparing file content
 * <li>file last changed date
 * <li>calculating a checksum
 * </ul>
 * 
 * Origin of code: Excalibur, Alexandria, Commons-Utils
 *
 * @author <a href="mailto:burton@relativity.yi.org">Kevin A. Burton</A>
 * @author <a href="mailto:sanders@apache.org">Scott Sanders</a>
 * @author <a href="mailto:dlr@finemaltcoding.com">Daniel Rall</a>
 * @author <a href="mailto:Christoph.Reck@dlr.de">Christoph.Reck</a>
 * @author <a href="mailto:peter@apache.org">Peter Donald</a>
 * @author <a href="mailto:jefft@apache.org">Jeff Turner</a>
 * @author Matthew Hawthorne
 * @author <a href="mailto:jeremias@apache.org">Jeremias Maerki</a>
 * @author Stephen Colebourne
 * @author Ian Springer
 * @author Chris Eldredge
 * @author Jim Harrington
 * @author Niall Pemberton
 * @author Sandy McArthur
 * @version $Id: FileUtils.java 507684 2007-02-14 20:38:25Z bayard $
 */
 public class FileUtils {
 
 /**
 * Instances should NOT be constructed in standard programming.
 */
 public FileUtils() {
 super();
 }
 
 /**
 * The number of bytes in a kilobyte.
 */
 public static final long ONE_KB = 1024;
 
 /**
 * The number of bytes in a megabyte.
 */
 public static final long ONE_MB = ONE_KB * ONE_KB;
 
 /**
 * The number of bytes in a gigabyte.
 */
 public static final long ONE_GB = ONE_KB * ONE_MB;
 
 /**
 * An empty array of type <code>File</code>.
 */
 public static final File[] EMPTY_FILE_ARRAY = new File[0];
 
 //-----------------------------------------------------------------------
 /**
 * Opens a {@link FileInputStream} for the specified file, providing better
 * error messages than simply calling <code>new FileInputStream(file)</code>.
 * 
 * At the end of the method either the stream will be successfully opened,
 * or an exception will have been thrown.
 * 
 * An exception is thrown if the file does not exist.
 * An exception is thrown if the file object exists but is a directory.
 * An exception is thrown if the file exists but cannot be read.
 * 
 * @param file the file to open for input, must not be <code>null</code>
 * @return a new {@link FileInputStream} for the specified file
 * @throws FileNotFoundException if the file does not exist
 * @throws IOException if the file object is a directory
 * @throws IOException if the file cannot be read
 * @since Commons IO 1.3
 */
 public static FileInputStream openInputStream(File file) throws IOException {
 if (file.exists()) {
 if (file.isDirectory()) {
 throw new IOException("File '" + file + "' exists but is a directory");
 }
 if (file.canRead() == false) {
 throw new IOException("File '" + file + "' cannot be read");
 }
 } else {
 throw new FileNotFoundException("File '" + file + "' does not exist");
 }
 return new FileInputStream(file);
 }
 
 //-----------------------------------------------------------------------
 /**
 * Opens a {@link FileOutputStream} for the specified file, checking and
 * creating the parent directory if it does not exist.
 * 
 * At the end of the method either the stream will be successfully opened,
 * or an exception will have been thrown.
 * 
 * The parent directory will be created if it does not exist.
 * The file will be created if it does not exist.
 * An exception is thrown if the file object exists but is a directory.
 * An exception is thrown if the file exists but cannot be written to.
 * An exception is thrown if the parent directory cannot be created.
 * 
 * @param file the file to open for output, must not be <code>null</code>
 * @return a new {@link FileOutputStream} for the specified file
 * @throws IOException if the file object is a directory
 * @throws IOException if the file cannot be written to
 * @throws IOException if a parent directory needs creating but that fails
 * @since Commons IO 1.3
 */
 public static FileOutputStream openOutputStream(File file) throws IOException {
 if (file.exists()) {
 if (file.isDirectory()) {
 throw new IOException("File '" + file + "' exists but is a directory");
 }
 if (file.canWrite() == false) {
 throw new IOException("File '" + file + "' cannot be written to");
 }
 } else {
 File parent = file.getParentFile();
 if (parent != null && parent.exists() == false) {
 if (parent.mkdirs() == false) {
 throw new IOException("File '" + file + "' could not be created");
 }
 }
 }
 return new FileOutputStream(file);
 }
 
 //-----------------------------------------------------------------------
 /**
 * Returns a human-readable version of the file size, where the input
 * represents a specific number of bytes.
 *
 * @param size the number of bytes
 * @return a human-readable display value (includes units)
 */
 public static String byteCountToDisplaySize(long size) {
 String displaySize;
 
 if (size / ONE_GB > 0) {
 displaySize = String.valueOf(size / ONE_GB) + " GB";
 } else if (size / ONE_MB > 0) {
 displaySize = String.valueOf(size / ONE_MB) + " MB";
 } else if (size / ONE_KB > 0) {
 displaySize = String.valueOf(size / ONE_KB) + " KB";
 } else {
 displaySize = String.valueOf(size) + " bytes";
 }
 return displaySize;
 }
 
 //-----------------------------------------------------------------------
 /**
 * Implements the same behaviour as the "touch" utility on Unix. It creates
 * a new file with size 0 or, if the file exists already, it is opened and
 * closed without modifying it, but updating the file date and time.
 * 
 * NOTE: As from v1.3, this method throws an IOException if the last
 * modified date of the file cannot be set. Also, as from v1.3 this method
 * creates parent directories if they do not exist.
 *
 * @param file the File to touch
 * @throws IOException If an I/O problem occurs
 */
 public static void touch(File file) throws IOException {
 if (!file.exists()) {
 OutputStream out = openOutputStream(file);
 IOUtils.closeQuietly(out);
 }
 boolean success = file.setLastModified(System.currentTimeMillis());
 if (!success) {
 throw new IOException("Unable to set the last modification time for " + file);
 }
 }
 
 //-----------------------------------------------------------------------
 /**
 * Converts a Collection containing java.io.File instanced into array
 * representation. This is to account for the difference between
 * File.listFiles() and FileUtils.listFiles().
 *
 * @param files a Collection containing java.io.File instances
 * @return an array of java.io.File
 */
 public static File[] convertFileCollectionToFileArray(Collection files) {
 return (File[]) files.toArray(new File[files.size()]);
 }
 
 //-----------------------------------------------------------------------
 /**
 * Finds files within a given directory (and optionally its
 * subdirectories). All files found are filtered by an IOFileFilter.
 *
 * @param files the collection of files found.
 * @param directory the directory to search in.
 * @param filter the filter to apply to files and directories.
 */
 private static void innerListFiles(Collection files, File directory,
 IOFileFilter filter) {
 File[] found = directory.listFiles((FileFilter) filter);
 if (found != null) {
 for (int i = 0; i < found.length; i++) {
 if (found[i].isDirectory()) {
 innerListFiles(files, found[i], filter);
 } else {
 files.add(found[i]);
 }
 }
 }
 }
 
 /**
 * Finds files within a given directory (and optionally its
 * subdirectories). All files found are filtered by an IOFileFilter.
 * 
 * If your search should recurse into subdirectories you can pass in
 * an IOFileFilter for directories. You don't need to bind a
 * DirectoryFileFilter (via logical AND) to this filter. This method does
 * that for you.
 * 
 * An example: If you want to search through all directories called
 * "temp" you pass in <code>FileFilterUtils.NameFileFilter("temp")</code>
 * 
 * Another common usage of this method is find files in a directory
 * tree but ignoring the directories generated CVS. You can simply pass
 * in <code>FileFilterUtils.makeCVSAware(null)</code>.
 *
 * @param directory the directory to search in
 * @param fileFilter filter to apply when finding files.
 * @param dirFilter optional filter to apply when finding subdirectories.
 * If this parameter is <code>null</code>, subdirectories will not be included in the
 * search. Use TrueFileFilter.INSTANCE to match all directories.
 * @return an collection of java.io.File with the matching files
 * @see org.apache.commons.io.filefilter.FileFilterUtils
 * @see org.apache.commons.io.filefilter.NameFileFilter
 */
 public static Collection listFiles(
 File directory, IOFileFilter fileFilter, IOFileFilter dirFilter) {
 if (!directory.isDirectory()) {
 throw new IllegalArgumentException(
 "Parameter 'directory' is not a directory");
 }
 if (fileFilter == null) {
 throw new NullPointerException("Parameter 'fileFilter' is null");
 }
 
 //Setup effective file filter
 IOFileFilter effFileFilter = FileFilterUtils.andFileFilter(fileFilter,
 FileFilterUtils.notFileFilter(DirectoryFileFilter.INSTANCE));
 
 //Setup effective directory filter
 IOFileFilter effDirFilter;
 if (dirFilter == null) {
 effDirFilter = FalseFileFilter.INSTANCE;
 } else {
 effDirFilter = FileFilterUtils.andFileFilter(dirFilter,
 DirectoryFileFilter.INSTANCE);
 }
 
 //Find files
 Collection files = new java.util.LinkedList();
 innerListFiles(files, directory,
 FileFilterUtils.orFileFilter(effFileFilter, effDirFilter));
 return files;
 }
 
 /**
 * Allows iteration over the files in given directory (and optionally
 * its subdirectories).
 * 
 * All files found are filtered by an IOFileFilter. This method is
 * based on {@link #listFiles(File, IOFileFilter, IOFileFilter)}.
 *
 * @param directory the directory to search in
 * @param fileFilter filter to apply when finding files.
 * @param dirFilter optional filter to apply when finding subdirectories.
 * If this parameter is <code>null</code>, subdirectories will not be included in the
 * search. Use TrueFileFilter.INSTANCE to match all directories.
 * @return an iterator of java.io.File for the matching files
 * @see org.apache.commons.io.filefilter.FileFilterUtils
 * @see org.apache.commons.io.filefilter.NameFileFilter
 * @since Commons IO 1.2
 */
 public static Iterator iterateFiles(
 File directory, IOFileFilter fileFilter, IOFileFilter dirFilter) {
 return listFiles(directory, fileFilter, dirFilter).iterator();
 }
 
 //-----------------------------------------------------------------------
 /**
 * Converts an array of file extensions to suffixes for use
 * with IOFileFilters.
 *
 * @param extensions an array of extensions. Format: {"java", "xml"}
 * @return an array of suffixes. Format: {".java", ".xml"}
 */
 private static String[] toSuffixes(String[] extensions) {
 String[] suffixes = new String[extensions.length];
 for (int i = 0; i < extensions.length; i++) {
 suffixes[i] = "." + extensions[i];
 }
 return suffixes;
 }
 
 
 /**
 * Finds files within a given directory (and optionally its subdirectories)
 * which match an array of extensions.
 *
 * @param directory the directory to search in
 * @param extensions an array of extensions, ex. {"java","xml"}. If this
 * parameter is <code>null</code>, all files are returned.
 * @param recursive if true all subdirectories are searched as well
 * @return an collection of java.io.File with the matching files
 */
 public static Collection listFiles(
 File directory, String[] extensions, boolean recursive) {
 IOFileFilter filter;
 if (extensions == null) {
 filter = TrueFileFilter.INSTANCE;
 } else {
 String[] suffixes = toSuffixes(extensions);
 filter = new SuffixFileFilter(suffixes);
 }
 return listFiles(directory, filter,
 (recursive ? TrueFileFilter.INSTANCE : FalseFileFilter.INSTANCE));
 }
 
 /**
 * Allows iteration over the files in a given directory (and optionally
 * its subdirectories) which match an array of extensions. This method
 * is based on {@link #listFiles(File, String[], boolean)}.
 *
 * @param directory the directory to search in
 * @param extensions an array of extensions, ex. {"java","xml"}. If this
 * parameter is <code>null</code>, all files are returned.
 * @param recursive if true all subdirectories are searched as well
 * @return an iterator of java.io.File with the matching files
 * @since Commons IO 1.2
 */
 public static Iterator iterateFiles(
 File directory, String[] extensions, boolean recursive) {
 return listFiles(directory, extensions, recursive).iterator();
 }
 
 //-----------------------------------------------------------------------
 /**
 * Compare the contents of two files to determine if they are equal or not.
 * 
 * This method checks to see if the two files are different lengths
 * or if they point to the same file, before resorting to byte-by-byte
 * comparison of the contents.
 * 
 * Code origin: Avalon
 *
 * @param file1 the first file
 * @param file2 the second file
 * @return true if the content of the files are equal or they both don't
 * exist, false otherwise
 * @throws IOException in case of an I/O error
 */
 public static boolean contentEquals(File file1, File file2) throws IOException {
 boolean file1Exists = file1.exists();
 if (file1Exists != file2.exists()) {
 return false;
 }
 
 if (!file1Exists) {
 // two not existing files are equal
 return true;
 }
 
 if (file1.isDirectory() || file2.isDirectory()) {
 // don't want to compare directory contents
 throw new IOException("Can't compare directories, only files");
 }
 
 if (file1.length() != file2.length()) {
 // lengths differ, cannot be equal
 return false;
 }
 
 if (file1.getCanonicalFile().equals(file2.getCanonicalFile())) {
 // same file
 return true;
 }
 
 InputStream input1 = null;
 InputStream input2 = null;
 try {
 input1 = new FileInputStream(file1);
 input2 = new FileInputStream(file2);
 return IOUtils.contentEquals(input1, input2);
 
 } finally {
 IOUtils.closeQuietly(input1);
 IOUtils.closeQuietly(input2);
 }
 }
 
 //-----------------------------------------------------------------------
 /**
 * Convert from a <code>URL</code> to a <code>File</code>.
 * 
 * From version 1.1 this method will decode the URL.
 * Syntax such as <code>file:///my%20docs/file.txt</code> will be
 * correctly decoded to <code>/my docs/file.txt</code>.
 *
 * @param url the file URL to convert, <code>null</code> returns <code>null</code>
 * @return the equivalent <code>File</code> object, or <code>null</code>
 * if the URL's protocol is not <code>file</code>
 * @throws IllegalArgumentException if the file is incorrectly encoded
 */
 public static File toFile(URL url) {
 if (url == null || !url.getProtocol().equals("file")) {
 return null;
 } else {
 String filename = url.getFile().replace('/', File.separatorChar);
 int pos =0;
 while ((pos = filename.indexOf('%', pos)) >= 0) {
 if (pos + 2 < filename.length()) {
 String hexStr = filename.substring(pos + 1, pos + 3);
 char ch = (char) Integer.parseInt(hexStr, 16);
 filename = filename.substring(0, pos) + ch + filename.substring(pos + 3);
 }
 }
 return new File(filename);
 }
 }
 
 /**
 * Converts each of an array of <code>URL</code> to a <code>File</code>.
 * 
 * Returns an array of the same size as the input.
 * If the input is <code>null</code>, an empty array is returned.
 * If the input contains <code>null</code>, the output array contains <code>null</code> at the same
 * index.
 * 
 * This method will decode the URL.
 * Syntax such as <code>file:///my%20docs/file.txt</code> will be
 * correctly decoded to <code>/my docs/file.txt</code>.
 *
 * @param urls the file URLs to convert, <code>null</code> returns empty array
 * @return a non-<code>null</code> array of Files matching the input, with a <code>null</code> item
 * if there was a <code>null</code> at that index in the input array
 * @throws IllegalArgumentException if any file is not a URL file
 * @throws IllegalArgumentException if any file is incorrectly encoded
 * @since Commons IO 1.1
 */
 public static File[] toFiles(URL[] urls) {
 if (urls == null || urls.length == 0) {
 return EMPTY_FILE_ARRAY;
 }
 File[] files = new File[urls.length];
 for (int i = 0; i < urls.length; i++) {
 URL url = urls[i];
 if (url != null) {
 if (url.getProtocol().equals("file") == false) {
 throw new IllegalArgumentException(
 "URL could not be converted to a File: " + url);
 }
 files[i] = toFile(url);
 }
 }
 return files;
 }
 
 /**
 * Converts each of an array of <code>File</code> to a <code>URL</code>.
 * 
 * Returns an array of the same size as the input.
 *
 * @param files the files to convert
 * @return an array of URLs matching the input
 * @throws IOException if a file cannot be converted
 */
 public static URL[] toURLs(File[] files) throws IOException {
 URL[] urls = new URL[files.length];
 
 for (int i = 0; i < urls.length; i++) {
 urls[i] = files[i].toURL();
 }
 
 return urls;
 }
 
 //-----------------------------------------------------------------------
 /**
 * Copies a file to a directory preserving the file date.
 * 
 * This method copies the contents of the specified source file
 * to a file of the same name in the specified destination directory.
 * The destination directory is created if it does not exist.
 * If the destination file exists, then this method will overwrite it.
 *
 * @param srcFile an existing file to copy, must not be <code>null</code>
 * @param destDir the directory to place the copy in, must not be <code>null</code>
 *
 * @throws NullPointerException if source or destination is null
 * @throws IOException if source or destination is invalid
 * @throws IOException if an IO error occurs during copying
 * @see #copyFile(File, File, boolean)
 */
 public static void copyFileToDirectory(File srcFile, File destDir) throws IOException {
 copyFileToDirectory(srcFile, destDir, true);
 }
 
 /**
 * Copies a file to a directory optionally preserving the file date.
 * 
 * This method copies the contents of the specified source file
 * to a file of the same name in the specified destination directory.
 * The destination directory is created if it does not exist.
 * If the destination file exists, then this method will overwrite it.
 *
 * @param srcFile an existing file to copy, must not be <code>null</code>
 * @param destDir the directory to place the copy in, must not be <code>null</code>
 * @param preserveFileDate true if the file date of the copy
 * should be the same as the original
 *
 * @throws NullPointerException if source or destination is <code>null</code>
 * @throws IOException if source or destination is invalid
 * @throws IOException if an IO error occurs during copying
 * @see #copyFile(File, File, boolean)
 * @since Commons IO 1.3
 */
 public static void copyFileToDirectory(File srcFile, File destDir, boolean preserveFileDate) throws IOException {
 if (destDir == null) {
 throw new NullPointerException("Destination must not be null");
 }
 if (destDir.exists() && destDir.isDirectory() == false) {
 throw new IllegalArgumentException("Destination '" + destDir + "' is not a directory");
 }
 copyFile(srcFile, new File(destDir, srcFile.getName()), preserveFileDate);
 }
 
 /**
 * Copies a file to a new location preserving the file date.
 * 
 * This method copies the contents of the specified source file to the
 * specified destination file. The directory holding the destination file is
 * created if it does not exist. If the destination file exists, then this
 * method will overwrite it.
 * 
 * @param srcFile an existing file to copy, must not be <code>null</code>
 * @param destFile the new file, must not be <code>null</code>
 * 
 * @throws NullPointerException if source or destination is <code>null</code>
 * @throws IOException if source or destination is invalid
 * @throws IOException if an IO error occurs during copying
 * @see #copyFileToDirectory(File, File)
 */
 public static void copyFile(File srcFile, File destFile) throws IOException {
 copyFile(srcFile, destFile, true);
 }
 
 /**
 * Copies a file to a new location.
 * 
 * This method copies the contents of the specified source file
 * to the specified destination file.
 * The directory holding the destination file is created if it does not exist.
 * If the destination file exists, then this method will overwrite it.
 *
 * @param srcFile an existing file to copy, must not be <code>null</code>
 * @param destFile the new file, must not be <code>null</code>
 * @param preserveFileDate true if the file date of the copy
 * should be the same as the original
 *
 * @throws NullPointerException if source or destination is <code>null</code>
 * @throws IOException if source or destination is invalid
 * @throws IOException if an IO error occurs during copying
 * @see #copyFileToDirectory(File, File, boolean)
 */
 public static void copyFile(File srcFile, File destFile,
 boolean preserveFileDate) throws IOException {
 if (srcFile == null) {
 throw new NullPointerException("Source must not be null");
 }
 if (destFile == null) {
 throw new NullPointerException("Destination must not be null");
 }
 if (srcFile.exists() == false) {
 throw new FileNotFoundException("Source '" + srcFile + "' does not exist");
 }
 if (srcFile.isDirectory()) {
 throw new IOException("Source '" + srcFile + "' exists but is a directory");
 }
 if (srcFile.getCanonicalPath().equals(destFile.getCanonicalPath())) {
 throw new IOException("Source '" + srcFile + "' and destination '" + destFile + "' are the same");
 }
 if (destFile.getParentFile() != null && destFile.getParentFile().exists() == false) {
 if (destFile.getParentFile().mkdirs() == false) {
 throw new IOException("Destination '" + destFile + "' directory cannot be created");
 }
 }
 if (destFile.exists() && destFile.canWrite() == false) {
 throw new IOException("Destination '" + destFile + "' exists but is read-only");
 }
 doCopyFile(srcFile, destFile, preserveFileDate);
 }
 
 /**
 * Internal copy file method.
 * 
 * @param srcFile the validated source file, must not be <code>null</code>
 * @param destFile the validated destination file, must not be <code>null</code>
 * @param preserveFileDate whether to preserve the file date
 * @throws IOException if an error occurs
 */
 private static void doCopyFile(File srcFile, File destFile, boolean preserveFileDate) throws IOException {
 if (destFile.exists() && destFile.isDirectory()) {
 throw new IOException("Destination '" + destFile + "' exists but is a directory");
 }
 
 FileInputStream input = new FileInputStream(srcFile);
 try {
 FileOutputStream output = new FileOutputStream(destFile);
 try {
 IOUtils.copy(input, output);
 } finally {
 IOUtils.closeQuietly(output);
 }
 } finally {
 IOUtils.closeQuietly(input);
 }
 
 if (srcFile.length() != destFile.length()) {
 throw new IOException("Failed to copy full contents from '" +
 srcFile + "' to '" + destFile + "'");
 }
 if (preserveFileDate) {
 destFile.setLastModified(srcFile.lastModified());
 }
 }
 
 //-----------------------------------------------------------------------
 /**
 * Copies a directory to within another directory preserving the file dates.
 * 
 * This method copies the source directory and all its contents to a
 * directory of the same name in the specified destination directory.
 * 
 * The destination directory is created if it does not exist.
 * If the destination directory did exist, then this method merges
 * the source with the destination, with the source taking precedence.
 *
 * @param srcDir an existing directory to copy, must not be <code>null</code>
 * @param destDir the directory to place the copy in, must not be <code>null</code>
 *
 * @throws NullPointerException if source or destination is <code>null</code>
 * @throws IOException if source or destination is invalid
 * @throws IOException if an IO error occurs during copying
 * @since Commons IO 1.2
 */
 public static void copyDirectoryToDirectory(File srcDir, File destDir) throws IOException {
 if (srcDir == null) {
 throw new NullPointerException("Source must not be null");
 }
 if (srcDir.exists() && srcDir.isDirectory() == false) {
 throw new IllegalArgumentException("Source '" + destDir + "' is not a directory");
 }
 if (destDir == null) {
 throw new NullPointerException("Destination must not be null");
 }
 if (destDir.exists() && destDir.isDirectory() == false) {
 throw new IllegalArgumentException("Destination '" + destDir + "' is not a directory");
 }
 copyDirectory(srcDir, new File(destDir, srcDir.getName()), true);
 }
 
 /**
 * Copies a whole directory to a new location preserving the file dates.
 * 
 * This method copies the specified directory and all its child
 * directories and files to the specified destination.
 * The destination is the new location and name of the directory.
 * 
 * The destination directory is created if it does not exist.
 * If the destination directory did exist, then this method merges
 * the source with the destination, with the source taking precedence.
 *
 * @param srcDir an existing directory to copy, must not be <code>null</code>
 * @param destDir the new directory, must not be <code>null</code>
 *
 * @throws NullPointerException if source or destination is <code>null</code>
 * @throws IOException if source or destination is invalid
 * @throws IOException if an IO error occurs during copying
 * @since Commons IO 1.1
 */
 public static void copyDirectory(File srcDir, File destDir) throws IOException {
 copyDirectory(srcDir, destDir, true);
 }
 
 /**
 * Copies a whole directory to a new location.
 * 
 * This method copies the contents of the specified source directory
 * to within the specified destination directory.
 * 
 * The destination directory is created if it does not exist.
 * If the destination directory did exist, then this method merges
 * the source with the destination, with the source taking precedence.
 *
 * @param srcDir an existing directory to copy, must not be <code>null</code>
 * @param destDir the new directory, must not be <code>null</code>
 * @param preserveFileDate true if the file date of the copy
 * should be the same as the original
 *
 * @throws NullPointerException if source or destination is <code>null</code>
 * @throws IOException if source or destination is invalid
 * @throws IOException if an IO error occurs during copying
 * @since Commons IO 1.1
 */
 public static void copyDirectory(File srcDir, File destDir,
 boolean preserveFileDate) throws IOException {
 if (srcDir == null) {
 throw new NullPointerException("Source must not be null");
 }
 if (destDir == null) {
 throw new NullPointerException("Destination must not be null");
 }
 if (srcDir.exists() == false) {
 throw new FileNotFoundException("Source '" + srcDir + "' does not exist");
 }
 if (srcDir.isDirectory() == false) {
 throw new IOException("Source '" + srcDir + "' exists but is not a directory");
 }
 if (srcDir.getCanonicalPath().equals(destDir.getCanonicalPath())) {
 throw new IOException("Source '" + srcDir + "' and destination '" + destDir + "' are the same");
 }
 doCopyDirectory(srcDir, destDir, preserveFileDate);
 }
 
 /**
 * Internal copy directory method.
 * 
 * @param srcDir the validated source directory, must not be <code>null</code>
 * @param destDir the validated destination directory, must not be <code>null</code>
 * @param preserveFileDate whether to preserve the file date
 * @throws IOException if an error occurs
 * @since Commons IO 1.1
 */
 private static void doCopyDirectory(File srcDir, File destDir, boolean preserveFileDate) throws IOException {
 if (destDir.exists()) {
 if (destDir.isDirectory() == false) {
 throw new IOException("Destination '" + destDir + "' exists but is not a directory");
 }
 } else {
 if (destDir.mkdirs() == false) {
 throw new IOException("Destination '" + destDir + "' directory cannot be created");
 }
 if (preserveFileDate) {
 destDir.setLastModified(srcDir.lastModified());
 }
 }
 if (destDir.canWrite() == false) {
 throw new IOException("Destination '" + destDir + "' cannot be written to");
 }
 // recurse
 File[] files = srcDir.listFiles();
 if (files == null) { // null if security restricted
 throw new IOException("Failed to list contents of " + srcDir);
 }
 for (int i = 0; i < files.length; i++) {
 File copiedFile = new File(destDir, files[i].getName());
 if (files[i].isDirectory()) {
 doCopyDirectory(files[i], copiedFile, preserveFileDate);
 } else {
 doCopyFile(files[i], copiedFile, preserveFileDate);
 }
 }
 }
 
 //-----------------------------------------------------------------------
 /**
 * Copies bytes from the URL <code>source</code> to a file
 * <code>destination</code>. The directories up to <code>destination</code>
 * will be created if they don't already exist. <code>destination</code>
 * will be overwritten if it already exists.
 *
 * @param source the <code>URL</code> to copy bytes from, must not be <code>null</code>
 * @param destination the non-directory <code>File</code> to write bytes to
 * (possibly overwriting), must not be <code>null</code>
 * @throws IOException if <code>source</code> URL cannot be opened
 * @throws IOException if <code>destination</code> is a directory
 * @throws IOException if <code>destination</code> cannot be written
 * @throws IOException if <code>destination</code> needs creating but can't be
 * @throws IOException if an IO error occurs during copying
 */
 public static void copyURLToFile(URL source, File destination) throws IOException {
 InputStream input = source.openStream();
 try {
 FileOutputStream output = openOutputStream(destination);
 try {
 IOUtils.copy(input, output);
 } finally {
 IOUtils.closeQuietly(output);
 }
 } finally {
 IOUtils.closeQuietly(input);
 }
 }
 
 //-----------------------------------------------------------------------
 /**
 * Recursively delete a directory.
 *
 * @param directory directory to delete
 * @throws IOException in case deletion is unsuccessful
 */
 public static void deleteDirectory(File directory) throws IOException {
 if (!directory.exists()) {
 return;
 }
 
 cleanDirectory(directory);
 if (!directory.delete()) {
 String message =
 "Unable to delete directory " + directory + ".";
 throw new IOException(message);
 }
 }
 
 /**
 * Clean a directory without deleting it.
 *
 * @param directory directory to clean
 * @throws IOException in case cleaning is unsuccessful
 */
 public static void cleanDirectory(File directory) throws IOException {
 if (!directory.exists()) {
 String message = directory + " does not exist";
 throw new IllegalArgumentException(message);
 }
 
 if (!directory.isDirectory()) {
 String message = directory + " is not a directory";
 throw new IllegalArgumentException(message);
 }
 
 File[] files = directory.listFiles();
 if (files == null) { // null if security restricted
 throw new IOException("Failed to list contents of " + directory);
 }
 
 IOException exception = null;
 for (int i = 0; i < files.length; i++) {
 File file = files[i];
 try {
 forceDelete(file);
 } catch (IOException ioe) {
 exception = ioe;
 }
 }
 
 if (null != exception) {
 throw exception;
 }
 }
 
 //-----------------------------------------------------------------------
 /**
 * Waits for NFS to propagate a file creation, imposing a timeout.
 * 
 * This method repeatedly tests {@link File#exists()} until it returns
 * true up to the maximum time specified in seconds.
 *
 * @param file the file to check, must not be <code>null</code>
 * @param seconds the maximum time in seconds to wait
 * @return true if file exists
 * @throws NullPointerException if the file is <code>null</code>
 */
 public static boolean waitFor(File file, int seconds) {
 int timeout = 0;
 int tick = 0;
 while (!file.exists()) {
 if (tick++ >= 10) {
 tick = 0;
 if (timeout++ > seconds) {
 return false;
 }
 }
 try {
 Thread.sleep(100);
 } catch (InterruptedException ignore) {
 // ignore exception
 } catch (Exception ex) {
 break;
 }
 }
 return true;
 }
 
 //-----------------------------------------------------------------------
 /**
 * Reads the contents of a file into a String.
 * The file is always closed.
 *
 * @param file the file to read, must not be <code>null</code>
 * @param encoding the encoding to use, <code>null</code> means platform default
 * @return the file contents, never <code>null</code>
 * @throws IOException in case of an I/O error
 * @throws java.io.UnsupportedEncodingException if the encoding is not supported by the VM
 */
 public static String readFileToString(File file, String encoding) throws IOException {
 InputStream in = null;
 try {
 in = openInputStream(file);
 return IOUtils.toString(in, encoding);
 } finally {
 IOUtils.closeQuietly(in);
 }
 }
 
 
 /**
 * Reads the contents of a file into a String using the default encoding for the VM. 
 * The file is always closed.
 *
 * @param file the file to read, must not be <code>null</code>
 * @return the file contents, never <code>null</code>
 * @throws IOException in case of an I/O error
 * @since Commons IO 1.3.1
 */
 public static String readFileToString(File file) throws IOException {
 return readFileToString(file, null);
 }
 
 /**
 * Reads the contents of a file into a byte array.
 * The file is always closed.
 *
 * @param file the file to read, must not be <code>null</code>
 * @return the file contents, never <code>null</code>
 * @throws IOException in case of an I/O error
 * @since Commons IO 1.1
 */
 public static byte[] readFileToByteArray(File file) throws IOException {
 InputStream in = null;
 try {
 in = openInputStream(file);
 return IOUtils.toByteArray(in);
 } finally {
 IOUtils.closeQuietly(in);
 }
 }
 
 /**
 * Reads the contents of a file line by line to a List of Strings.
 * The file is always closed.
 *
 * @param file the file to read, must not be <code>null</code>
 * @param encoding the encoding to use, <code>null</code> means platform default
 * @return the list of Strings representing each line in the file, never <code>null</code>
 * @throws IOException in case of an I/O error
 * @throws java.io.UnsupportedEncodingException if the encoding is not supported by the VM
 * @since Commons IO 1.1
 */
 public static List readLines(File file, String encoding) throws IOException {
 InputStream in = null;
 try {
 in = openInputStream(file);
 return IOUtils.readLines(in, encoding);
 } finally {
 IOUtils.closeQuietly(in);
 }
 }
 
 /**
 * Reads the contents of a file line by line to a List of Strings using the default encoding for the VM.
 * The file is always closed.
 *
 * @param file the file to read, must not be <code>null</code>
 * @return the list of Strings representing each line in the file, never <code>null</code>
 * @throws IOException in case of an I/O error
 * @since Commons IO 1.3
 */
 public static List readLines(File file) throws IOException {
 return readLines(file, null);
 }
 
 /**
 * Return an Iterator for the lines in a <code>File</code>.
 * 
 * This method opens an <code>InputStream</code> for the file.
 * When you have finished with the iterator you should close the stream
 * to free internal resources. This can be done by calling the
 * {@link LineIterator#close()} or
 * {@link LineIterator#closeQuietly(LineIterator)} method.
 * 
 * The recommended usage pattern is:
 * <pre>
 * LineIterator it = FileUtils.lineIterator(file, "UTF-8");
 * try {
 * while (it.hasNext()) {
 * String line = it.nextLine();
 * /// do something with line
 * }
 * } finally {
 * LineIterator.closeQuietly(iterator);
 * }
 * </pre>
 * 
 * If an exception occurs during the creation of the iterator, the
 * underlying stream is closed.
 *
 * @param file the file to open for input, must not be <code>null</code>
 * @param encoding the encoding to use, <code>null</code> means platform default
 * @return an Iterator of the lines in the file, never <code>null</code>
 * @throws IOException in case of an I/O error (file closed)
 * @since Commons IO 1.2
 */
 public static LineIterator lineIterator(File file, String encoding) throws IOException {
 InputStream in = null;
 try {
 in = openInputStream(file);
 return IOUtils.lineIterator(in, encoding);
 } catch (IOException ex) {
 IOUtils.closeQuietly(in);
 throw ex;
 } catch (RuntimeException ex) {
 IOUtils.closeQuietly(in);
 throw ex;
 }
 }
 
 /**
 * Return an Iterator for the lines in a <code>File</code> using the default encoding for the VM.
 *
 * @param file the file to open for input, must not be <code>null</code>
 * @return an Iterator of the lines in the file, never <code>null</code>
 * @throws IOException in case of an I/O error (file closed)
 * @since Commons IO 1.3
 * @see #lineIterator(File, String)
 */
 public static LineIterator lineIterator(File file) throws IOException {
 return lineIterator(file, null);
 }
 
 //-----------------------------------------------------------------------
 /**
 * Writes a String to a file creating the file if it does not exist.
 *
 * NOTE: As from v1.3, the parent directories of the file will be created
 * if they do not exist.
 *
 * @param file the file to write
 * @param data the content to write to the file
 * @param encoding the encoding to use, <code>null</code> means platform default
 * @throws IOException in case of an I/O error
 * @throws java.io.UnsupportedEncodingException if the encoding is not supported by the VM
 */
 public static void writeStringToFile(File file, String data, String encoding) throws IOException {
 OutputStream out = null;
 try {
 out = openOutputStream(file);
 IOUtils.write(data, out, encoding);
 } finally {
 IOUtils.closeQuietly(out);
 }
 }
 
 /**
 * Writes a String to a file creating the file if it does not exist using the default encoding for the VM.
 * 
 * @param file the file to write
 * @param data the content to write to the file
 * @throws IOException in case of an I/O error
 */
 public static void writeStringToFile(File file, String data) throws IOException {
 writeStringToFile(file, data, null);
 }
 
 /**
 * Writes a byte array to a file creating the file if it does not exist.
 * 
 * NOTE: As from v1.3, the parent directories of the file will be created
 * if they do not exist.
 *
 * @param file the file to write to
 * @param data the content to write to the file
 * @throws IOException in case of an I/O error
 * @since Commons IO 1.1
 */
 public static void writeByteArrayToFile(File file, byte[] data) throws IOException {
 OutputStream out = null;
 try {
 out = openOutputStream(file);
 out.write(data);
 } finally {
 IOUtils.closeQuietly(out);
 }
 }
 
 /**
 * Writes the <code>toString()</code> value of each item in a collection to
 * the specified <code>File</code> line by line.
 * The specified character encoding and the default line ending will be used.
 * 
 * NOTE: As from v1.3, the parent directories of the file will be created
 * if they do not exist.
 *
 * @param file the file to write to
 * @param encoding the encoding to use, <code>null</code> means platform default
 * @param lines the lines to write, <code>null</code> entries produce blank lines
 * @throws IOException in case of an I/O error
 * @throws java.io.UnsupportedEncodingException if the encoding is not supported by the VM
 * @since Commons IO 1.1
 */
 public static void writeLines(File file, String encoding, Collection lines) throws IOException {
 writeLines(file, encoding, lines, null);
 }
 
 /**
 * Writes the <code>toString()</code> value of each item in a collection to
 * the specified <code>File</code> line by line.
 * The default VM encoding and the default line ending will be used.
 *
 * @param file the file to write to
 * @param lines the lines to write, <code>null</code> entries produce blank lines
 * @throws IOException in case of an I/O error
 * @since Commons IO 1.3
 */
 public static void writeLines(File file, Collection lines) throws IOException {
 writeLines(file, null, lines, null);
 }
 
 /**
 * Writes the <code>toString()</code> value of each item in a collection to
 * the specified <code>File</code> line by line.
 * The specified character encoding and the line ending will be used.
 * 
 * NOTE: As from v1.3, the parent directories of the file will be created
 * if they do not exist.
 *
 * @param file the file to write to
 * @param encoding the encoding to use, <code>null</code> means platform default
 * @param lines the lines to write, <code>null</code> entries produce blank lines
 * @param lineEnding the line separator to use, <code>null</code> is system default
 * @throws IOException in case of an I/O error
 * @throws java.io.UnsupportedEncodingException if the encoding is not supported by the VM
 * @since Commons IO 1.1
 */
 public static void writeLines(File file, String encoding, Collection lines, String lineEnding) throws IOException {
 OutputStream out = null;
 try {
 out = openOutputStream(file);
 IOUtils.writeLines(lines, lineEnding, out, encoding);
 } finally {
 IOUtils.closeQuietly(out);
 }
 }
 
 /**
 * Writes the <code>toString()</code> value of each item in a collection to
 * the specified <code>File</code> line by line.
 * The default VM encoding and the specified line ending will be used.
 *
 * @param file the file to write to
 * @param lines the lines to write, <code>null</code> entries produce blank lines
 * @param lineEnding the line separator to use, <code>null</code> is system default
 * @throws IOException in case of an I/O error
 * @since Commons IO 1.3
 */
 public static void writeLines(File file, Collection lines, String lineEnding) throws IOException {
 writeLines(file, null, lines, lineEnding);
 }
 
 //-----------------------------------------------------------------------
 /**
 * Delete a file. If file is a directory, delete it and all sub-directories.
 * 
 * The difference between File.delete() and this method are:
 * <ul>
 * <li>A directory to be deleted does not have to be empty.</li>
 * <li>You get exceptions when a file or directory cannot be deleted.
 * (java.io.File methods returns a boolean)</li>
 * </ul>
 *
 * @param file file or directory to delete, must not be <code>null</code>
 * @throws NullPointerException if the directory is <code>null</code>
 * @throws IOException in case deletion is unsuccessful
 */
 public static void forceDelete(File file) throws IOException {
 if (file.isDirectory()) {
 deleteDirectory(file);
 } else {
 if (!file.exists()) {
 throw new FileNotFoundException("File does not exist: " + file);
 }
 if (!file.delete()) {
 String message =
 "Unable to delete file: " + file;
 throw new IOException(message);
 }
 }
 }
 
 /**
 * Schedule a file to be deleted when JVM exits.
 * If file is directory delete it and all sub-directories.
 *
 * @param file file or directory to delete, must not be <code>null</code>
 * @throws NullPointerException if the file is <code>null</code>
 * @throws IOException in case deletion is unsuccessful
 */
 public static void forceDeleteOnExit(File file) throws IOException {
 if (file.isDirectory()) {
 deleteDirectoryOnExit(file);
 } else {
 file.deleteOnExit();
 }
 }
 
 /**
 * Recursively schedule directory for deletion on JVM exit.
 *
 * @param directory directory to delete, must not be <code>null</code>
 * @throws NullPointerException if the directory is <code>null</code>
 * @throws IOException in case deletion is unsuccessful
 */
 private static void deleteDirectoryOnExit(File directory) throws IOException {
 if (!directory.exists()) {
 return;
 }
 
 cleanDirectoryOnExit(directory);
 directory.deleteOnExit();
 }
 
 /**
 * Clean a directory without deleting it.
 *
 * @param directory directory to clean, must not be <code>null</code>
 * @throws NullPointerException if the directory is <code>null</code>
 * @throws IOException in case cleaning is unsuccessful
 */
 private static void cleanDirectoryOnExit(File directory) throws IOException {
 if (!directory.exists()) {
 String message = directory + " does not exist";
 throw new IllegalArgumentException(message);
 }
 
 if (!directory.isDirectory()) {
 String message = directory + " is not a directory";
 throw new IllegalArgumentException(message);
 }
 
 File[] files = directory.listFiles();
 if (files == null) { // null if security restricted
 throw new IOException("Failed to list contents of " + directory);
 }
 
 IOException exception = null;
 for (int i = 0; i < files.length; i++) {
 File file = files[i];
 try {
 forceDeleteOnExit(file);
 } catch (IOException ioe) {
 exception = ioe;
 }
 }
 
 if (null != exception) {
 throw exception;
 }
 }
 
 /**
 * Make a directory, including any necessary but nonexistent parent
 * directories. If there already exists a file with specified name or
 * the directory cannot be created then an exception is thrown.
 *
 * @param directory directory to create, must not be <code>null</code>
 * @throws NullPointerException if the directory is <code>null</code>
 * @throws IOException if the directory cannot be created
 */
 public static void forceMkdir(File directory) throws IOException {
 if (directory.exists()) {
 if (directory.isFile()) {
 String message =
 "File "
 + directory
 + " exists and is "
 + "not a directory. Unable to create directory.";
 throw new IOException(message);
 }
 } else {
 if (!directory.mkdirs()) {
 String message =
 "Unable to create directory " + directory;
 throw new IOException(message);
 }
 }
 }
 
 //-----------------------------------------------------------------------
 /**
 * Recursively count size of a directory (sum of the length of all files).
 *
 * @param directory directory to inspect, must not be <code>null</code>
 * @return size of directory in bytes, 0 if directory is security restricted
 * @throws NullPointerException if the directory is <code>null</code>
 */
 public static long sizeOfDirectory(File directory) {
 if (!directory.exists()) {
 String message = directory + " does not exist";
 throw new IllegalArgumentException(message);
 }
 
 if (!directory.isDirectory()) {
 String message = directory + " is not a directory";
 throw new IllegalArgumentException(message);
 }
 
 long size = 0;
 
 File[] files = directory.listFiles();
 if (files == null) { // null if security restricted
 return 0L;
 }
 for (int i = 0; i < files.length; i++) {
 File file = files[i];
 
 if (file.isDirectory()) {
 size += sizeOfDirectory(file);
 } else {
 size += file.length();
 }
 }
 
 return size;
 }
 
 //-----------------------------------------------------------------------
 /**
 * Tests if the specified <code>File</code> is newer than the reference
 * <code>File</code>.
 *
 * @param file the <code>File</code> of which the modification date must
 * be compared, must not be <code>null</code>
 * @param reference the <code>File</code> of which the modification date
 * is used, must not be <code>null</code>
 * @return true if the <code>File</code> exists and has been modified more
 * recently than the reference <code>File</code>
 * @throws IllegalArgumentException if the file is <code>null</code>
 * @throws IllegalArgumentException if the reference file is <code>null</code> or doesn't exist
 */
 public static boolean isFileNewer(File file, File reference) {
 if (reference == null) {
 throw new IllegalArgumentException("No specified reference file");
 }
 if (!reference.exists()) {
 throw new IllegalArgumentException("The reference file '"
 + file + "' doesn't exist");
 }
 return isFileNewer(file, reference.lastModified());
 }
 
 /**
 * Tests if the specified <code>File</code> is newer than the specified
 * <code>Date</code>.
 * 
 * @param file the <code>File</code> of which the modification date
 * must be compared, must not be <code>null</code>
 * @param date the date reference, must not be <code>null</code>
 * @return true if the <code>File</code> exists and has been modified
 * after the given <code>Date</code>.
 * @throws IllegalArgumentException if the file is <code>null</code>
 * @throws IllegalArgumentException if the date is <code>null</code>
 */
 public static boolean isFileNewer(File file, Date date) {
 if (date == null) {
 throw new IllegalArgumentException("No specified date");
 }
 return isFileNewer(file, date.getTime());
 }
 
 /**
 * Tests if the specified <code>File</code> is newer than the specified
 * time reference.
 *
 * @param file the <code>File</code> of which the modification date must
 * be compared, must not be <code>null</code>
 * @param timeMillis the time reference measured in milliseconds since the
 * epoch (00:00:00 GMT, January 1, 1970)
 * @return true if the <code>File</code> exists and has been modified after
 * the given time reference.
 * @throws IllegalArgumentException if the file is <code>null</code>
 */
 public static boolean isFileNewer(File file, long timeMillis) {
 if (file == null) {
 throw new IllegalArgumentException("No specified file");
 }
 if (!file.exists()) {
 return false;
 }
 return file.lastModified() > timeMillis;
 }
 
 
 //-----------------------------------------------------------------------
 /**
 * Tests if the specified <code>File</code> is older than the reference
 * <code>File</code>.
 *
 * @param file the <code>File</code> of which the modification date must
 * be compared, must not be <code>null</code>
 * @param reference the <code>File</code> of which the modification date
 * is used, must not be <code>null</code>
 * @return true if the <code>File</code> exists and has been modified before
 * the reference <code>File</code>
 * @throws IllegalArgumentException if the file is <code>null</code>
 * @throws IllegalArgumentException if the reference file is <code>null</code> or doesn't exist
 */
 public static boolean isFileOlder(File file, File reference) {
 if (reference == null) {
 throw new IllegalArgumentException("No specified reference file");
 }
 if (!reference.exists()) {
 throw new IllegalArgumentException("The reference file '"
 + file + "' doesn't exist");
 }
 return isFileOlder(file, reference.lastModified());
 }
 
 /**
 * Tests if the specified <code>File</code> is older than the specified
 * <code>Date</code>.
 * 
 * @param file the <code>File</code> of which the modification date
 * must be compared, must not be <code>null</code>
 * @param date the date reference, must not be <code>null</code>
 * @return true if the <code>File</code> exists and has been modified
 * before the given <code>Date</code>.
 * @throws IllegalArgumentException if the file is <code>null</code>
 * @throws IllegalArgumentException if the date is <code>null</code>
 */
 public static boolean isFileOlder(File file, Date date) {
 if (date == null) {
 throw new IllegalArgumentException("No specified date");
 }
 return isFileOlder(file, date.getTime());
 }
 
 /**
 * Tests if the specified <code>File</code> is older than the specified
 * time reference.
 *
 * @param file the <code>File</code> of which the modification date must
 * be compared, must not be <code>null</code>
 * @param timeMillis the time reference measured in milliseconds since the
 * epoch (00:00:00 GMT, January 1, 1970)
 * @return true if the <code>File</code> exists and has been modified before
 * the given time reference.
 * @throws IllegalArgumentException if the file is <code>null</code>
 */
 public static boolean isFileOlder(File file, long timeMillis) {
 if (file == null) {
 throw new IllegalArgumentException("No specified file");
 }
 if (!file.exists()) {
 return false;
 }
 return file.lastModified() < timeMillis;
 }
 
 //-----------------------------------------------------------------------
 /**
 * Computes the checksum of a file using the CRC32 checksum routine.
 * The value of the checksum is returned.
 *
 * @param file the file to checksum, must not be <code>null</code>
 * @return the checksum value
 * @throws NullPointerException if the file or checksum is <code>null</code>
 * @throws IllegalArgumentException if the file is a directory
 * @throws IOException if an IO error occurs reading the file
 * @since Commons IO 1.3
 */
 public static long checksumCRC32(File file) throws IOException {
 CRC32 crc = new CRC32();
 checksum(file, crc);
 return crc.getValue();
 }
 
 /**
 * Computes the checksum of a file using the specified checksum object.
 * Multiple files may be checked using one <code>Checksum</code> instance
 * if desired simply by reusing the same checksum object.
 * For example:
 * <pre>
 * long csum = FileUtils.checksum(file, new CRC32()).getValue();
 * </pre>
 *
 * @param file the file to checksum, must not be <code>null</code>
 * @param checksum the checksum object to be used, must not be <code>null</code>
 * @return the checksum specified, updated with the content of the file
 * @throws NullPointerException if the file or checksum is <code>null</code>
 * @throws IllegalArgumentException if the file is a directory
 * @throws IOException if an IO error occurs reading the file
 * @since Commons IO 1.3
 */
 public static Checksum checksum(File file, Checksum checksum) throws IOException {
 if (file.isDirectory()) {
 throw new IllegalArgumentException("Checksums can't be computed on directories");
 }
 InputStream in = null;
 try {
 in = new CheckedInputStream(new FileInputStream(file), checksum);
 IOUtils.copy(in, new NullOutputStream());
 } finally {
 IOUtils.closeQuietly(in);
 }
 return checksum;
 }
 
 }