Java 输入/输出——File类

2022-10-28 10:32:38

　　File类是java.io包下代表与平台无关的文件和目录，也就是说，如果希望在程序中操作文件和目录，都可以通过File类来完成。值得指出的是，不管是文件还是目录都是使用File来操作的，File能新建、删除、重命名文件和目录，File不能访问文件内容本身。如果需要访问文件内容本身，则需要使用输入/输出流。

　　File类相关的方法参考链接：https://docs.oracle.com/javase/9/docs/api/overview-summary.html

Field Summary

Fields
Modifier and Type	Field	Description
`static String`	`pathSeparator`	The system-dependent path-separator character, represented as a string for convenience.
`static char`	`pathSeparatorChar`	The system-dependent path-separator character.
`static String`	`separator`	The system-dependent default name-separator character, represented as a string for convenience.
`static char`	`separatorChar`	The system-dependent default name-separator character.

Constructor Summary

Constructors
Constructor	Description
`File(File parent, String child)`	Creates a new `File` instance from a parent abstract pathname and a child pathname string.
`File(String pathname)`	Creates a new `File` instance by converting the given pathname string into an abstract pathname.
`File(String parent, String child)`	Creates a new `File` instance from a parent pathname string and a child pathname string.
`File(URI uri)`	Creates a new `File` instance by converting the given `file:` URI into an abstract pathname.

Method Summary

All MethodsStatic Methods Instance Methods Concrete Methods Deprecated Methods
Modifier and Type	Method	Description
`boolean`	`canExecute()`	Tests whether the application can execute the file denoted by this abstract pathname.
`boolean`	`canRead()`	Tests whether the application can read the file denoted by this abstract pathname.
`boolean`	`canWrite()`	Tests whether the application can modify the file denoted by this abstract pathname.
`int`	`compareTo(File pathname)`	Compares two abstract pathnames lexicographically.
`boolean`	`createNewFile()`	Atomically creates a new, empty file named by this abstract pathname if and only if a file with this name does not yet exist.
`static File`	`createTempFile(String prefix,String suffix)`	Creates an empty file in the default temporary-file directory, using the given prefix and suffix to generate its name.
`static File`	`createTempFile(String prefix,String suffix,File directory)`	Creates a new empty file in the specified directory, using the given prefix and suffix strings to generate its name.
`boolean`	`delete()`	Deletes the file or directory denoted by this abstract pathname.
`void`	`deleteOnExit()`	Requests that the file or directory denoted by this abstract pathname be deleted when the virtual machine terminates.
`boolean`	`equals(Object obj)`	Tests this abstract pathname for equality with the given object.
`boolean`	`exists()`	Tests whether the file or directory denoted by this abstract pathname exists.
`File`	`getAbsoluteFile()`	Returns the absolute form of this abstract pathname.
`String`	`getAbsolutePath()`	Returns the absolute pathname string of this abstract pathname.
`File`	`getCanonicalFile()`	Returns the canonical form of this abstract pathname.
`String`	`getCanonicalPath()`	Returns the canonical pathname string of this abstract pathname.
`long`	`getFreeSpace()`	Returns the number of unallocated bytes in the partition named by this abstract path name.
`String`	`getName()`	Returns the name of the file or directory denoted by this abstract pathname.
`String`	`getParent()`	Returns the pathname string of this abstract pathname's parent, or `null` if this pathname does not name a parent directory.
`File`	`getParentFile()`	Returns the abstract pathname of this abstract pathname's parent, or `null` if this pathname does not name a parent directory.
`String`	`getPath()`	Converts this abstract pathname into a pathname string.
`long`	`getTotalSpace()`	Returns the size of the partition named by this abstract pathname.
`long`	`getUsableSpace()`	Returns the number of bytes available to this virtual machine on the partition named by this abstract pathname.
`int`	`hashCode()`	Computes a hash code for this abstract pathname.
`boolean`	`isAbsolute()`	Tests whether this abstract pathname is absolute.
`boolean`	`isDirectory()`	Tests whether the file denoted by this abstract pathname is a directory.
`boolean`	`isFile()`	Tests whether the file denoted by this abstract pathname is a normal file.
`boolean`	`isHidden()`	Tests whether the file named by this abstract pathname is a hidden file.
`long`	`lastModified()`	Returns the time that the file denoted by this abstract pathname was last modified.
`long`	`length()`	Returns the length of the file denoted by this abstract pathname.
`String[]`	`list()`	Returns an array of strings naming the files and directories in the directory denoted by this abstract pathname.
`String[]`	`list(FilenameFilter filter)`	Returns an array of strings naming the files and directories in the directory denoted by this abstract pathname that satisfy the specified filter.
`File[]`	`listFiles()`	Returns an array of abstract pathnames denoting the files in the directory denoted by this abstract pathname.
`File[]`	`listFiles(FileFilter filter)`	Returns an array of abstract pathnames denoting the files and directories in the directory denoted by this abstract pathname that satisfy the specified filter.
`File[]`	`listFiles(FilenameFilter filter)`	Returns an array of abstract pathnames denoting the files and directories in the directory denoted by this abstract pathname that satisfy the specified filter.
`static File[]`	`listRoots()`	List the available filesystem roots.
`boolean`	`mkdir()`	Creates the directory named by this abstract pathname.
`boolean`	`mkdirs()`	Creates the directory named by this abstract pathname, including any necessary but nonexistent parent directories.
`boolean`	`renameTo(File dest)`	Renames the file denoted by this abstract pathname.
`boolean`	`setExecutable(boolean executable)`	A convenience method to set the owner's execute permission for this abstract pathname.
`boolean`	`setExecutable(boolean executable, boolean ownerOnly)`	Sets the owner's or everybody's execute permission for this abstract pathname.
`boolean`	`setLastModified(long time)`	Sets the last-modified time of the file or directory named by this abstract pathname.
`boolean`	`setReadable(boolean readable)`	A convenience method to set the owner's read permission for this abstract pathname.
`boolean`	`setReadable(boolean readable, boolean ownerOnly)`	Sets the owner's or everybody's read permission for this abstract pathname.
`boolean`	`setReadOnly()`	Marks the file or directory named by this abstract pathname so that only read operations are allowed.
`boolean`	`setWritable(boolean writable)`	A convenience method to set the owner's write permission for this abstract pathname.
`boolean`	`setWritable(boolean writable, boolean ownerOnly)`	Sets the owner's or everybody's write permission for this abstract pathname.
`Path`	`toPath()`	Returns a `java.nio.file.Path` object constructed from the this abstract path.
`String`	`toString()`	Returns the pathname string of this abstract pathname.
`URI`	`toURI()`	Constructs a `file:` URI that represents this abstract pathname.
`URL`	`toURL()`	Deprecated. This method does not automatically escape characters that are illegal in URLs. It is recommended that new code convert an abstract pathname into a URL by first converting it into a URI, via the `toURI`method, and then converting the URI into a URL via the `URI.toURL` method.

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, wait, wait, wait

1、访问文件和目录

 package com.zyjhandsome.io;

 import java.io.*;

 public class FileTest {

     public static void main(String[] args) throws IOException

     {

         // 以当前路径来创建一个File对象

         File file = new File(".");

         // 直接获取文件名, 输出一点

         System.out.println(file.getName());

         // 获取相对路径的父路径可能出错, 下面代码输出null

         System.out.println(file.getParent());

         // 获取绝对路径

         System.out.println(file.getAbsoluteFile());

         // 获取绝对路径

         System.out.println(file.getAbsoluteFile().getParent());

         // 当前路径下创建一个临时文件

         File tmpFile = File.createTempFile("aaa", ".txt", file);

         // 指定当JVM退出时候删除该文件

         tmpFile.deleteOnExit();

         // 以系统当前时间作为新文件名来创建新文件

         File newFile = new File(System.currentTimeMillis() + "");

         System.out.println("newFile对象是否存在1: " + newFile.exists());

         // 以指定newFile对象来创建一个文件

         newFile.createNewFile();

         System.out.println("newFile对象是否存在2: " + newFile.exists());

         // 以newFile对象来创建一个目录，因为newFile已经存在，所以下面方法返回false, 即无法创建该目录

         System.out.println("newFile.mkdir():" + newFile.mkdir());

         System.out.println("----------------------");

         // 使用list()方法列出当前路径下的所有文件和路径

         String[] fileList = file.list();

         for (String fileName : fileList)

         {

             System.out.println(fileName);

         }

         System.out.println("----------------------");

         // listRoots()静态方法列出所有的磁盘根路径

         File[] roots = File.listRoots();

         System.out.println("====系统所有根路径如下====");

         for (File root : roots)

         {

             System.out.println(root);

         }

     }

 }

 .

 null

 D:\zhaoyingjun\eclipse-workspace\CollectionTest\.

 D:\zhaoyingjun\eclipse-workspace\CollectionTest

 newFile对象是否存在1: false

 newFile对象是否存在2: true

 newFile.mkdir():false

 ----------------------

 .classpath

 .project

 .settings

 1537712414564

 1537712424492

 1537712893895

 1537712926829

 1537712940906

 1537713158525

 1537713167968

 1537774060515

 aaa1610208071466755969.txt

 bin

 src

 ----------------------

 ====系统所有根路径如下====

 C:\

 D:\

2、文件过滤器

　　在File类的list()方法中可以接收一个FilenameFilter参数，通过该参数可以只列出符合条件的文件。这里的FilenameFilter接口和javax.swing.filechooser包下的FileFilter抽象类的功能非常相似，可以把FileFilter当成是FilenameFilter的实现类。

　　FilenameFilter接口里包含了一个accept(File dir, String name)方法，该方法将依次对指定File的所有子目录或者文件进行迭代，如果该方法返回true，则list()方法会列出该子目录或者文件。

 package com.zyjhandsome.io;

 import java.io.*;

 public class FilenameFilterTest {

     public static void main(String[] args) {

         // TODO Auto-generated method stub

         File file = new File(".");

         // 使用Lambda表达式(目标类型是FilenameFilter)实现文件过滤器

         // 如果文件名以.java结尾, 或者文件对应一个路径，则返回true

         String[] nameList = file.list((dir, name) ->

             name.endsWith(".java") || new File(name).isDirectory());

         for (String name : nameList)

         {

             System.out.println(name);

         }

     }

 }

 .settings

 bin

 src

码农公寓

Field Summary

Constructor Summary

Method Summary

Methods inherited from class java.lang.Object

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