Java IO

File 类

File 类：它既可以代表一个特定文件的名字，也可以代表目录内一系列文件的名字。若代表一个文件集，便可用list()方法查询这个集，返回的是一个字串数组。
把File看成某个路径下的一系列东西
File的构造函数为：File file = new File(“某个路径”);
就是根据某个路径新建File对象

例1：查看当前目录下有啥文件或文件夹

import java.util.regex.*;import java.io.File;import java.io.FilenameFilter;import java.util.*;public class DirList {  public static void main(String[] args) {    // ”.”或”.\”代表当前目录,这个目录也就是jvm启动路径，可以打印出来看看路径    File file = new File(".");    System.out.println(file.getAbsolutePath());    String[] list;    if(args.length == 0)      list = file.list();    else      list = file.list(new DirFilter(args[0]));    // 匹配任意字符    //list = file.list(new DirFilter("[\\d\\D]*"));    // 匹配以b开头的文件夹或文件    //list = file.list(new DirFilter("^b.*"));    Arrays.sort(list, String.CASE_INSENSITIVE_ORDER);    for(String dirItem : list)      System.out.println(dirItem);  }}class DirFilter implements FilenameFilter {      private Pattern pattern;      public DirFilter(String regex) {        pattern = Pattern.compile(regex);      }      // 判断某个name是否匹配正则表达式      public boolean accept(File dir, String name) {        return pattern.matcher(name).matches();      }}结果：D:\Java\eclipse_se\lifan_workspace\firstProject\..classpath.project.settingsbinmylibsrc注：自己写了一个正则表达式过滤器，当用它过滤时，比如只找以b开头的文件（夹）list = file.list(new DirFilter("^b.*"));最后只会得到 bin这一个文件夹

精简写法：

import java.util.regex.*;import java.io.*;import java.util.*;public class DirList3 {  public static void main(final String[] args) {    File path = new File(".");    String[] list;    if(args.length == 0)      list = path.list();    else      list = path.list(new FilenameFilter() {        private Pattern pattern = Pattern.compile(args[0]);        public boolean accept(File dir, String name) {          return pattern.matcher(name).matches();        }      });    Arrays.sort(list, String.CASE_INSENSITIVE_ORDER);    for(String dirItem : list)      System.out.println(dirItem);  }}

有关File的一些操作
例如
File f = new File(“…”);
创建文件夹 f.mkdirs();
删除文件（夹） f.delete();
例2：

import java.io.*;public class MakeDirectories {  private static void usage() {    System.err.println(      "Usage:MakeDirectories path1 ...\n" +      "Creates each path\n" +      "Usage:MakeDirectories -d path1 ...\n" +      "Deletes each path\n" +      "Usage:MakeDirectories -r path1 path2\n" +      "Renames from path1 to path2");    System.exit(1);  }  //  查看file的信息  private static void fileData(File f) {    System.out.println(      "Absolute path: " + f.getAbsolutePath() +      "\n Can read: " + f.canRead() +      "\n Can write: " + f.canWrite() +      "\n getName: " + f.getName() +      "\n getParent: " + f.getParent() +      "\n getPath: " + f.getPath() +      "\n length: " + f.length() +      "\n lastModified: " + f.lastModified());    if(f.isFile())      System.out.println("It's a file");    else if(f.isDirectory())      System.out.println("It's a directory");  }  public static void main(String[] args) {    if(args.length < 1) usage();    // 重命名    if(args[0].equals("-r")) {      if(args.length != 3) usage();      File        old = new File(args[1]),        rname = new File(args[2]);      old.renameTo(rname);      fileData(old);      fileData(rname);      return; // Exit main    }    int count = 0;    boolean del = false;    if(args[0].equals("-d")) {      count++;      del = true;    }    count--;    while(++count < args.length) {      File f = new File(args[count]);      if(f.exists()) {        System.out.println(f + " exists");        if(del) {          System.out.println("deleting..." + f);          f.delete();        }      }      else { // Doesn't exist        if(!del) {          f.mkdirs();          System.out.println("created " + f);        }      }      fileData(f);    }  }}