QQ账号登录	立即注册>>

您现在的位置：论坛 › 资料库 › JAVA开发 > Java File类总结和FileUtils类

总共48086条微博

动态微博

发表新帖

查看: 4726|回复: 0

Java File类总结和FileUtils类

admin

1244 主题	544 听众	1万金钱

管理员

TA的每日心情

	衰 2021-2-2 11:21

签到天数: 36 天

[LV.5]常住居民I

电梯直达

楼主

发表于 2015-04-23 09:04:20 |只看该作者 |倒序浏览

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>
* .
*
* 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}
* @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.
*
* 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}
* @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.
*
* 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.
*
* 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

复制代码

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

科帮网 1、本主题所有言论和图片纯属会员个人意见，与本社区立场无关
2、本站所有主题由该帖子作者发表，该帖子作者与科帮网享有帖子相关版权
3、其他单位或个人使用、转载或引用本文时必须同时征得该帖子作者和科帮网的同意
4、帖子作者须承担一切因本文发表而直接或间接导致的民事或刑事法律责任
5、本帖部分内容转载自其它媒体，但并不代表本站赞同其观点和对其真实性负责
6、如本帖侵犯到任何版权问题，请立即告知本站，本站将及时予与删除并致以最深的歉意
7、科帮网管理员和版主有权不事先通知发贴者而删除本文