Java File类总结和FileUtils类

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");
}
}

}

FileUtils.java

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

　　本博客旧博文：

　　Java IO File类

　　Java IO 用递归实现目录删除和树形目录展示 Java实现