Java File类总结和FileUtils类

文件存在和类型判断

　　创建出File类的对象并不代表该路径下有此文件或目录。

　　用public boolean exists()可以判断文件是否存在。

 

　　File类的对象可以是目录或者文件。

　　如果是目录，public boolean isDirectory()返回true；

　　如果是文件(非目录则是文件)，public boolean isFile()返回true；

　　但是注意需要先判断文件是否存在，如果文件不存在，上面两个方法都返回false,即不存在的File类对象既不是文件也不是目录。

 

创建文件

　　public boolean createNewFile()会创建一个新的空文件，只有该文件不存在的时候会创建，如果文件已经存在的话则返回false。

创建文件夹

　　public boolean mkdir()

　　创建目录，成功返回true。只能创建一个文件夹，要求所有的父目录都存在，否则创建失败。

　　public boolean mkdirs()

　　创建目录，成功返回true，会创建所有不存在的父目录。(注意即便最后创建失败，但是也可能创建了一些中间目录)。

　　上面两个方法如果要创建的目录已经存在，不再重新创建，都返回false，只有新建目录返回true。

 

目录操作

　　列出目录中的文件有以下方法可选：

　　String[] list() 

　　String[] list(FilenameFilter filter) 

　　返回文件名数组。

　　File[] listFiles() 

　　File[] listFiles(FileFilter filter) 

　　File[] listFiles(FilenameFilter filter) 

　　返回File数组。

 

　　参数是文件或者文件名过滤器。

 

　　注意返回为空和返回为null的意义是不同的。

　　若不包含(符合条件的)文件，返回为空。

　　但是如果返回为null，则表明调用方法的File对象可能不是一个目录，或者发生了IO错误。

 

删除文件

　　boolean delete()方法会删除文件，如果File对象是文件则直接删除，对于目录来说，如果是空目录则直接删除，非空目录则无法删除，返回false。

　　如果要删除的文件不能被删除则会抛出IOException。

 

　　注意：不论是创建文件、创建目录还是删除文件，只有在动作真正发生的时候会返回true。

 

FileUtils类

　　在项目中写一些工具类包装通用操作是很有必要的，看了一下apache的FileUtils类，copy了一些方法出来：

/* * 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 com.mengdd.file;import java.io.File;import java.io.FileInputStream;import java.io.FileNotFoundException;import java.io.FileOutputStream;import java.io.IOException;/* * FileUtils copied from org.apache.commons.io.FileUtils */public class FileUtils {    /**     * Construct a file from the set of name elements.     *     * @param directory     *            the parent directory     * @param names     *            the name elements     * @return the file     */    public static File getFile(File directory, String... names) {        if (directory == null) {            throw new NullPointerException(                    "directorydirectory must not be null");        }        if (names == null) {            throw new NullPointerException("names must not be null");        }        File file = directory;        for (String name : names) {            file = new File(file, name);        }        return file;    }    /**     * Construct a file from the set of name elements.     *     * @param names     *            the name elements     * @return the file     */    public static File getFile(String... names) {        if (names == null) {            throw new NullPointerException("names must not be null");        }        File file = null;        for (String name : names) {            if (file == null) {                file = new File(name);            }            else {                file = new File(file, name);            }        }        return file;    }    /**     * Opens a {@link FileInputStream} for the specified file, providing better     * error messages than simply calling <code>new FileInputStream(file)</code>     * .     * <p>     * At the end of the method either the stream will be successfully opened,     * or an exception will have been thrown.     * <p>     * 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}     * @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     */    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.     * <p>     * At the end of the method either the stream will be successfully opened,     * or an exception will have been thrown.     * <p>     * 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}     * @param append     *            if {@code true}, then bytes will be added to the     *            end of the file rather than overwriting     * @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     */    public static FileOutputStream openOutputStream(File file, boolean append)            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) {                if (!parent.mkdirs() && !parent.isDirectory()) {                    throw new IOException("Directory '" + parent                            + "' could not be created");                }            }        }        return new FileOutputStream(file, append);    }    public static FileOutputStream openOutputStream(File file)            throws IOException {        return openOutputStream(file, false);    }    /**     * Cleans 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 (File file : files) {            try {                forceDelete(file);            }            catch (IOException ioe) {                exception = ioe;            }        }        if (null != exception) {            throw exception;        }    }    // -----------------------------------------------------------------------    /**     * Deletes a directory recursively.     *     * @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);        }    }    /**     * Deletes a file. If file is a directory, delete it and all     * sub-directories.     * <p>     * 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}     * @throws NullPointerException     *             if the directory is {@code null}     * @throws FileNotFoundException     *             if the file was not found     * @throws IOException     *             in case deletion is unsuccessful     */    public static void forceDelete(File file) throws IOException {        if (file.isDirectory()) {            deleteDirectory(file);        }        else {            boolean filePresent = file.exists();            if (!file.delete()) {                if (!filePresent) {                    throw new FileNotFoundException("File does not exist: "                            + file);                }                String message = "Unable to delete file: " + file;                throw new IOException(message);            }        }    }    /**     * Deletes a file, never throwing an exception. If file is a directory,     * delete it and all sub-directories.     * <p>     * The difference between File.delete() and this method are:     * <ul>     * <li>A directory to be deleted does not have to be empty.</li>     * <li>No exceptions are thrown when a file or directory cannot be deleted.</li>     * </ul>     *     * @param file     *            file or directory to delete, can be {@code null}     * @return {@code true} if the file or directory was deleted, otherwise     *         {@code false}     *     */    public static boolean deleteQuietly(File file) {        if (file == null) {            return false;        }        try {            if (file.isDirectory()) {                cleanDirectory(file);            }        }        catch (Exception ignored) {        }        try {            return file.delete();        }        catch (Exception ignored) {            return false;        }    }    /**     * Makes a directory, including any necessary but nonexistent parent     * directories. If a file already exists with specified name but it is     * not a directory then an IOException is thrown.     * If the directory cannot be created (or does not already exist)     * then an IOException is thrown.     *     * @param directory     *            directory to create, must not be {@code null}     * @throws NullPointerException     *             if the directory is {@code null}     * @throws IOException     *             if the directory cannot be created or the file already exists     *             but is not a directory     */    public static void forceMkdir(File directory) throws IOException {        if (directory.exists()) {            if (!directory.isDirectory()) {                String message = "File " + directory + " exists and is "                        + "not a directory. Unable to create directory.";                throw new IOException(message);            }        }        else {            if (!directory.mkdirs()) {                // Double-check that some other thread or process hasn't made                // the directory in the background                if (!directory.isDirectory()) {                    String message = "Unable to create directory " + directory;                    throw new IOException(message);                }            }        }    }    /**     * Returns the size of the specified file or directory. If the provided     * {@link File} is a regular file, then the file's length is returned.     * If the argument is a directory, then the size of the directory is     * calculated recursively. If a directory or subdirectory is security     * restricted, its size will not be included.     *     * @param file     *            the regular file or directory to return the size     *            of (must not be {@code null}).     *     * @return the length of the file, or recursive size of the directory,     *         provided (in bytes).     *     * @throws NullPointerException     *             if the file is {@code null}     * @throws IllegalArgumentException     *             if the file does not exist.     *     */    public static long sizeOf(File file) {        if (!file.exists()) {            String message = file + " does not exist";            throw new IllegalArgumentException(message);        }        if (file.isDirectory()) {            return sizeOfDirectory(file);        }        else {            return file.length();        }    }    /**     * Counts the size of a directory recursively (sum of the length of all     * files).     *     * @param directory     *            directory to inspect, must not be {@code null}     * @return size of directory in bytes, 0 if directory is security     *         restricted, a negative number when the real total     *         is greater than {@link Long#MAX_VALUE}.     * @throws NullPointerException     *             if the directory is {@code null}     */    public static long sizeOfDirectory(File directory) {        checkDirectory(directory);        final File[] files = directory.listFiles();        if (files == null) { // null if security restricted            return 0L;        }        long size = 0;        for (final File file : files) {            size += sizeOf(file);            if (size < 0) {                break;            }        }        return size;    }    /**     * Checks that the given {@code File} exists and is a directory.     *     * @param directory     *            The {@code File} to check.     * @throws IllegalArgumentException     *             if the given {@code File} does not exist or is not a     *             directory.     */    private static void checkDirectory(File directory) {        if (!directory.exists()) {            throw new IllegalArgumentException(directory + " does not exist");        }        if (!directory.isDirectory()) {            throw new IllegalArgumentException(directory                    + " is not a directory");        }    }}

 

 

参考资料

　　File类官方文档：

　　http://docs.oracle.com/javase/7/docs/api/java/io/File.html

　　org.apache.commons.io.FileUtils源码：

　　http://grepcode.com/file/repo1.maven.org/maven2/commons-io/commons-io/2.4/org/apache/commons/io/FileUtils.java