java.io.File实战

There are many things that can go wrong:

• A class works in Unix but doesn't on Windows (or vice versa)
• Invalid filenames due to double or missing path separators
• UNC filenames (on Windows) don't work with my home-grown filename utility function

UNC (Universal Naming Convention)通用命名约定。windows目录或文件的 UNC 名称可以包括共享名称下的目录路径，格式为： \\servername\sharename\directory\filename。

一个在linux或windows移植的小技巧 System.getProperty("file.separator") 

1.These are good reasons not to work with filenames as Strings. Using java.io.File instead handles many of the above cases nicely.

 String tmpdir = "/var/tmp";
 String tmpfile = tmpdir + System.getProperty("file.separator") + "test.tmp";
 InputStream in = new FileInputStream(tmpfile);

改为下面的代码会更好：

 File tmpdir = new File("/var/tmp");
 File tmpfile = new File(tmpdir, "test.tmp");
 InputStream in = new FileInputStream(tmpfile);

2.下面是一个不好的方法：

 public static String getExtension(String filename) {
   int index = filename.lastIndexOf('.');
   if (index == -1) {
     return "";
   } else {
     return filename.substring(index + 1);
   }
 }

如果传入 "C:\Temp\documentation.new\README"则会返回"new\README"。但这不是我们想要的结果。

3.复制文件

public void copyFile() throws IOException{
        FileInputStream iStream = new FileInputStream(new File("a.txt"));
        FileOutputStream oStream = new FileOutputStream(new File("acopy.txt"));
        byte [] bytes = new byte[2048];
        while(iStream.read(bytes) != -1){
            oStream.write(bytes);
        }
        oStream.flush();
        oStream.close();
        iStream.close();
    }