Java NIO Files
Java NIO Files
The Java NIO Files
class (java.nio.file.Files
) provides several methods for manipulating files in the file system. This Java NIO Files
tutorial will cover the most commonly used of these methods. The Files
class contains many methods, so check the JavaDoc too, if you need a method that is not described here. The Files
class just might have a method for it still.
The java.nio.file.Files
class works with java.nio.file.Path
instances, so you need to understand the Path
class before you can work with the Files
class.
这个FIles类和Path类一起合作,你最好先了解一下Path类。FIles类有很多方法,你可以查javaDoc
Files.exists()
检查你创建的Path是否存在
The Files.exists()
method checks if a given Path
exists in the file system.
It is possible to create Path
instances that do not exist in the file system. For instance, if you plan to create a new directory, you would first create the corresponding Path
instance, and then create the directory.
Since Path
instances may or may not point to paths that exist in the file system, you can use the Files.exists()
method to determine if they do (in case you need to check that).
Here is a Java Files.exists()
example:
Path path = Paths.get("data/logging.properties"); boolean pathExists =
Files.exists(path,
new LinkOption[]{ LinkOption.NOFOLLOW_LINKS});
This example first creates a Path
instance pointing to the path we want to check if exists or not. Second, the example calls the Files.exists()
method with the Path
instance as the first parameter.
Notice the second parameter of the Files.exists()
method. This parameter is an array of options that influence how the Files.exists()
determines if the path exists or not. In this example above the array contains the LinkOption.NOFOLLOW_LINKS
which means that the Files.exists()
method should not follow symbolic links in the file system to determine if the path exists.
注意第二个参数,是一个数组,检查的条件
LinkOption.NOFOLLOW_LINKS 不遵循符号连接
Files.createDirectory()
创建path路径,存在的话会报错。
The Files.createDirectory()
method creates a new directory from a Path
instance. Here is a Java Files.createDirectory()
example:
Path path = Paths.get("data/subdir"); try {
Path newDir = Files.createDirectory(path);
} catch(FileAlreadyExistsException e){
// the directory already exists.
} catch (IOException e) {
//something else went wrong
e.printStackTrace();
}
The first line creates the Path
instance that represents the directory to create. Inside the try-catch
block the Files.createDirectory()
method is called with the path as parameter. If creating the directory succeeds, a Path
instance is returned which points to the newly created path.
If the directory already exists, a java.nio.file.FileAlreadyExistsException
will be thrown. If something else goes wrong, an IOException
may get thrown. For instance, if the parent directory of the desired, new directory does not exist, an IOException
may get thrown. The parent directory is the directory in which you want to create the new directory. Thus, it means the parent directory of the new directory.
Files.copy()
拷贝方法,从一个文件拷到另外一个文件,目标文件存在会报错
The Files.copy()
method copies a file from one path to another. Here is a Java NIO Files.copy()
example:
Path sourcePath = Paths.get("data/logging.properties");
Path destinationPath = Paths.get("data/logging-copy.properties"); try {
Files.copy(sourcePath, destinationPath);
} catch(FileAlreadyExistsException e) {
//destination file already exists
} catch (IOException e) {
//something else went wrong
e.printStackTrace();
}
First the example creates a source and destination Path
instance. Then the example calls Files.copy()
, passing the two Path
instances as parameters. This will result in the file referenced by the source path to be copied to the file referenced by the destination path.
If the destination file already exists, a java.nio.file.FileAlreadyExistsException
is thrown. If something else goes wrong, an IOException
will be thrown. For instance, if the directory to copy the file to does not exist, an IOException
will be thrown.
Overwriting Existing Files
注意后面的那个参数,替换已存在
It is possible to force the Files.copy()
to overwrite an existing file. Here an example showing how to overwrite an existing file using Files.copy()
:
Path sourcePath = Paths.get("data/logging.properties");
Path destinationPath = Paths.get("data/logging-copy.properties"); try {
Files.copy(sourcePath, destinationPath,
StandardCopyOption.REPLACE_EXISTING);
} catch(FileAlreadyExistsException e) {
//destination file already exists
} catch (IOException e) {
//something else went wrong
e.printStackTrace();
}
Notice the third parameter to the Files.copy()
method. This parameter instructs the copy()
method to overwrite an existing file if the destination file already exists.
Files.move()
移动一个文件并修改名称,第三个参数替换已存在
The Java NIO Files
class also contains a function for moving files from one path to another. Moving a file is the same as renaming it, except moving a file can both move it to a different directory and change its name in the same operation. Yes, the java.io.File
class could also do that with its renameTo()
method, but now you have the file move functionality in the java.nio.file.Files
class too.
Here is a Java Files.move()
example:
Path sourcePath = Paths.get("data/logging-copy.properties");
Path destinationPath = Paths.get("data/subdir/logging-moved.properties"); try {
Files.move(sourcePath, destinationPath,
StandardCopyOption.REPLACE_EXISTING);
} catch (IOException e) {
//moving file failed.
e.printStackTrace();
}
First the source path and destination path are created. The source path points to the file to move, and the destination path points to where the file should be moved to. Then the Files.move()
method is called. This results in the file being moved.
Notice the third parameter passed to Files.move()
. This parameter tells the Files.move()
method to overwrite any existing file at the destination path. This parameter is actually optional.
The Files.move()
method may throw an IOException
if moving the file fails. For instance, if a file already exists at the destination path, and you have left out the StandardCopyOption.REPLACE_EXISTING
option, or if the file to move does not exist etc.
Files.delete()
删掉一个文件
The Files.delete()
method can delete a file or directory. Here is a Java Files.delete()
example:
Path path = Paths.get("data/subdir/logging-moved.properties"); try {
Files.delete(path);
} catch (IOException e) {
//deleting file failed
e.printStackTrace();
}
First the Path
pointing to the file to delete is created. Second the Files.delete()
method is called. If the Files.delete()
fails to delete the file for some reason (e.g. the file or directory does not exist), an IOException
is thrown.
Files.walkFileTree()
遍历一个目录
The Files.walkFileTree()
method contains functionality for traversing a directory tree recursively. The walkFileTree()
method takes a Path
instance and a FileVisitor
as parameters. The Path
instance points to the directory you want to traverse. The FileVisitor
is called during traversion.
Before I explain how the traversal works, here is first the FileVisitor
interface:
public interface FileVisitor { public FileVisitResult preVisitDirectory(
Path dir, BasicFileAttributes attrs) throws IOException; public FileVisitResult visitFile(
Path file, BasicFileAttributes attrs) throws IOException; public FileVisitResult visitFileFailed(
Path file, IOException exc) throws IOException; public FileVisitResult postVisitDirectory(
Path dir, IOException exc) throws IOException { }
You have to implement the FileVisitor
interface yourself, and pass an instance of your implementation to the walkFileTree()
method. Each method of your FileVisitor
implementation will get called at different times during the directory traversal. If you do not need to hook into all of these methods, you can extend the SimpleFileVisitor
class, which contains default implementations of all methods in the FileVisitor
interface.
Here is a walkFileTree()
example:
Files.walkFileTree(path, new FileVisitor<Path>() {
@Override
public FileVisitResult preVisitDirectory(Path dir, BasicFileAttributes attrs) throws IOException {
System.out.println("pre visit dir:" + dir);
return FileVisitResult.CONTINUE;
} @Override
public FileVisitResult visitFile(Path file, BasicFileAttributes attrs) throws IOException {
System.out.println("visit file: " + file);
return FileVisitResult.CONTINUE;
} @Override
public FileVisitResult visitFileFailed(Path file, IOException exc) throws IOException {
System.out.println("visit file failed: " + file);
return FileVisitResult.CONTINUE;
} @Override
public FileVisitResult postVisitDirectory(Path dir, IOException exc) throws IOException {
System.out.println("post visit directory: " + dir);
return FileVisitResult.CONTINUE;
}
});
Each of the methods in the FileVisitor
implementation gets called at different times during traversal:
The preVisitDirectory()
method is called just before visiting any directory. The postVisitDirectory()
method is called just after visiting a directory.
The visitFile()
mehtod is called for every file visited during the file walk. It is not called for directories - only files. The visitFileFailed()
method is called in case visiting a file fails. For instance, if you do not have the right permissions, or something else goes wrong.
Each of the four methods return a FileVisitResult
enum instance. The FileVisitResult
enum contains the following four options:
CONTINUE
TERMINATE
SKIP_SIBLINGS
SKIP_SUBTREE
By returning one of these values the called method can decide how the file walk should continue.
CONTINUE
means that the file walk should continue as normal.
TERMINATE
means that the file walk should terminate now.
SKIP_SIBLINGS
means that the file walk should continue but without visiting any siblings of this file or directory.文件遍历继续,但是不要访问其他兄弟节点
SKIP_SUBTREE
means that the file walk should continue but without visiting the entries in this directory. This value only has a function if returned from preVisitDirectory()
. If returned from any other methods it will be interpreted as a CONTINUE
.文件遍历继续,但是不要访问这个文件的条目,这个只有在pre方法中返回。其他方法的话意味着继续
Searching For Files
上面的方法的具体实例,找一个文件名为README.txt 的文件
Here is a walkFileTree()
that extends SimpleFileVisitor
to look for a file named README.txt
:
Path rootPath = Paths.get("data");
String fileToFind = File.separator + "README.txt"; try {
Files.walkFileTree(rootPath, new SimpleFileVisitor<Path>() { @Override
public FileVisitResult visitFile(Path file, BasicFileAttributes attrs) throws IOException {
String fileString = file.toAbsolutePath().toString();
//System.out.println("pathString = " + fileString); if(fileString.endsWith(fileToFind)){
System.out.println("file found at path: " + file.toAbsolutePath());
return FileVisitResult.TERMINATE;
}
return FileVisitResult.CONTINUE;
}
});
} catch(IOException e){
e.printStackTrace();
}
Deleting Directories Recursively
循环删除文件和文件夹
The Files.walkFileTree()
can also be used to delete a directory with all files and subdirectories inside it. The Files.delete()
method will only delete a directory if it is empty. By walking through all directories and deleting all files (inside visitFile()
) in each directory, and afterwards delete the directory itself (inside postVisitDirectory()
) you can delete a directory with all subdirectories and files. Here is a recursive directory deletion example:
Path rootPath = Paths.get("data/to-delete"); try {
Files.walkFileTree(rootPath, new SimpleFileVisitor<Path>() {
@Override
public FileVisitResult visitFile(Path file, BasicFileAttributes attrs) throws IOException {
System.out.println("delete file: " + file.toString());
Files.delete(file);
return FileVisitResult.CONTINUE;
} @Override
public FileVisitResult postVisitDirectory(Path dir, IOException exc) throws IOException {
Files.delete(dir);
System.out.println("delete dir: " + dir.toString());
return FileVisitResult.CONTINUE;
}
});
} catch(IOException e){
e.printStackTrace();
}
Additional Methods in the Files Class
FIles类还有很多其他的方法哦,大家查可以看源代码查看方法。如:创建符号连接,查看文件大小,设置文件权限等方法。
The java.nio.file.Files
class contains many other useful functions, like functions for creating symbolic links, determining the file size, setting file permissions etc. Check out the JavaDoc for thejava.nio.file.Files
class for more information about these methods.
Java NIO Files的更多相关文章
- java nio Files.newDirectoryStream用法
try(DirectoryStream<Path> dirStream = Files.newDirectoryStream(Paths.get(directory,"*.ts& ...
- Java NIO学习系列七:Path、Files、AsynchronousFileChannel
相对于标准Java IO中通过File来指向文件和目录,Java NIO中提供了更丰富的类来支持对文件和目录的操作,不仅仅支持更多操作,还支持诸如异步读写等特性,本文我们就来学习一些Java NIO提 ...
- Java NIO 完全学习笔记(转)
本篇博客依照 Java NIO Tutorial翻译,算是学习 Java NIO 的一个读书笔记.建议大家可以去阅读原文,相信你肯定会受益良多. 1. Java NIO Tutorial Java N ...
- Java NIO 学习总结 学习手册
原文 并发编程网(翻译):http://ifeve.com/java-nio-all/ 源自 http://tutorials.jenkov.com/java-nio/index.html Java ...
- 海纳百川而来的一篇相当全面的Java NIO教程
目录 零.NIO包 一.Java NIO Channel通道 Channel的实现(Channel Implementations) Channel的基础示例(Basic Channel Exampl ...
- Java NIO Path
Java NIO Path Creating a Path Instance Creating an Absolute Path Creating a Relative Path Path.norma ...
- Java NIO Path接口和Files类配合操作文件
Java NIO Path接口和Files类配合操作文件 @author ixenos Path接口 1.Path表示的是一个目录名序列,其后还可以跟着一个文件名,路径中第一个部件是根部件时就是绝对路 ...
- JAVA NIO学习四:Path&Paths&Files 学习
今天我们将学习NIO 的最后一章,前面大部分涉及IO 和 NIO 的知识都已经讲过了,那么本章将要讲解的是关于Path 以及Paths 和 Files 相关的知识点,以对前面知识点的补充,好了言归正传 ...
- Java NIO之拥抱Path和Files
Java面试通关手册(Java学习指南)github地址(欢迎star和pull):https://github.com/Snailclimb/Java_Guide 历史回顾: Java NIO 概览 ...
随机推荐
- redis 过期时间与缓存
设置过期时间 redis对于存储的键值可以设置过期时间,对于过期了的键值,redis会自动删除. > OK > get price " > expire price (in ...
- python学习之----遍历单个域名和随机数
实现“维基百科六度分隔理论”的查找方法.也就是说,我们要实现从埃里克 · 艾德尔的词条页面(https://en.wikipedia.org/wiki/Eric_Idle)开始,经过最少的链接点击次数 ...
- (转)日期类型的input元素设置默认值为当天
原文地址 html5的form元素对日期时间有丰富的支持 <input type="date"> <input type="time"> ...
- PHPutf-8转码。
$str = 'jiaoqing.': echo mb_convert_encoding($str,"gbk","utf-8");
- HTML5 实现获取 gzip 压缩数据,并进行解压,同时解决汉字乱码,相关 pako.js
1, 下载 pako.js => http://nodeca.github.io/pako/#Deflate.prototype.onData 2, 首先需要了解一下 XMLHttpReques ...
- WIN10下VS CODE 更新后拓展宿主意外终止问题解决方法(每次系统更新都要删除一次git)
S CODE最近更新后,一打开就会出现拓展宿主意外终止的错误,点重新加载等都不好用. 出现这个问题主要是和git有关,做如下操作处理就好: 打开vscode安装文件夹->resource文件夹- ...
- AspxGridView使用手记
AspxGridView使用手记 一. 基本使用方法 4 1.导入Dll文件 4 2.Asp.Net页面控件注册 4 3. Asp.Net页面控件声明 5 4.删除licenses. ...
- 使用STM32的USART的同步模式Synchronous调戏SPI【usart模拟spi理论】
[原创出品§转载请注明出处] 出处:http://www.cnblogs.com/libra13179/p/7064321.html 什么东西?? 我们先来看我们平常看到SPI的时序图(呵呵,要是忘记 ...
- H5自动准备杂记
由于之前没做过UI自动化,近期准备做H5自动化,要学的东西还是很多. 1.本地debug环境:android studio + android SDK(想要调试通要关注:驱动.手机开发者模式要打开) ...
- Linux MySQL 安装、远程访问和密码重置
安装: yum install mysql yum install mysql-server yum install mysql-devel 设置开机启动: chkconfig -add mysqld ...