Java 輸入/輸出——File類

時間 2019-11-20

標籤 java 輸入輸出 file 欄目 Java 简体版

原文原文鏈接

　　File類是java.io包下表明與平臺無關的文件和目錄，也就是說，若是但願在程序中操做文件和目錄，均可以經過File類來完成。值得指出的是，無論是文件仍是目錄都是使用File來操做的，File能新建、刪除、重命名文件和目錄，File不能訪問文件內容自己。若是須要訪問文件內容自己，則須要使用輸入/輸出流。html

　　File類相關的方法參考連接：https://docs.oracle.com/javase/9/docs/api/overview-summary.htmljava

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 MethodsInstance MethodsConcrete MethodsDeprecated 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

一、訪問文件和目錄 api

 1 package com.zyjhandsome.io;
 2 
 3 import java.io.*;
 4 
 5 public class FileTest {
 6 
 7     public static void main(String[] args) throws IOException
 8     {
 9         // 以當前路徑來建立一個File對象
10         File file = new File(".");
11         // 直接獲取文件名, 輸出一點
12         System.out.println(file.getName());    
13         // 獲取相對路徑的父路徑可能出錯, 下面代碼輸出null
14         System.out.println(file.getParent());
15         // 獲取絕對路徑
16         System.out.println(file.getAbsoluteFile());
17         // 獲取絕對路徑
18         System.out.println(file.getAbsoluteFile().getParent());    
19         // 當前路徑下建立一個臨時文件
20         File tmpFile = File.createTempFile("aaa", ".txt", file);
21         // 指定當JVM退出時候刪除該文件
22         tmpFile.deleteOnExit();
23         // 以系統當前時間做爲新文件名來建立新文件
24         File newFile = new File(System.currentTimeMillis() + "");
25         System.out.println("newFile對象是否存在1: " + newFile.exists());
26         // 以指定newFile對象來建立一個文件
27         newFile.createNewFile();
28         System.out.println("newFile對象是否存在2: " + newFile.exists());
29         // 以newFile對象來建立一個目錄，由於newFile已經存在，因此下面方法返回false, 即沒法建立該目錄
30         System.out.println("newFile.mkdir():" + newFile.mkdir());
31         System.out.println("----------------------");
32         // 使用list()方法列出當前路徑下的全部文件和路徑
33         String[] fileList = file.list();
34         for (String fileName : fileList)
35         {
36             System.out.println(fileName);
37         }
38         System.out.println("----------------------");
39         // listRoots()靜態方法列出全部的磁盤根路徑
40         File[] roots = File.listRoots();
41         System.out.println("====系統全部根路徑以下====");
42         for (File root : roots)
43         {
44             System.out.println(root);
45         }
46     }
47 }

 1 .
 2 null
 3 D:\zhaoyingjun\eclipse-workspace\CollectionTest\.
 4 D:\zhaoyingjun\eclipse-workspace\CollectionTest
 5 newFile對象是否存在1: false
 6 newFile對象是否存在2: true
 7 newFile.mkdir():false
 8 ----------------------
 9 .classpath
10 .project
11 .settings
12 1537712414564
13 1537712424492
14 1537712893895
15 1537712926829
16 1537712940906
17 1537713158525
18 1537713167968
19 1537774060515
20 aaa1610208071466755969.txt
21 bin
22 src
23 ----------------------
24 ====系統全部根路徑以下====
25 C:\
26 D:\

二、文件過濾器oracle

　　在File類的list()方法中能夠接收一個FilenameFilter參數，經過該參數能夠只列出符合條件的文件。這裏的FilenameFilter接口和javax.swing.filechooser包下的FileFilter抽象類的功能很是類似，能夠把FileFilter當成是FilenameFilter的實現類。app

　　FilenameFilter接口裏包含了一個accept(File dir, String name)方法，該方法將依次對指定File的全部子目錄或者文件進行迭代，若是該方法返回true，則list()方法會列出該子目錄或者文件。eclipse

 1 package com.zyjhandsome.io;
 2 
 3 import java.io.*;
 4 
 5 public class FilenameFilterTest {
 6 
 7     public static void main(String[] args) {
 8         // TODO Auto-generated method stub
 9         File file = new File(".");
10         // 使用Lambda表達式(目標類型是FilenameFilter)實現文件過濾器
11         // 若是文件名以.java結尾, 或者文件對應一個路徑，則返回true
12         String[] nameList = file.list((dir, name) ->
13             name.endsWith(".java") || new File(name).isDirectory());
14         for (String name : nameList)
15         {
16             System.out.println(name);
17         }                
18     }    
19 }