以前我一直以為File#renameTo(File)方法與OS下面的 move/mv 指令是相同的，可以達到改名、移動檔案的目的。不過後來經常發現問題：File#renameTo(File)方法會傳回失敗(false)，檔案沒有移動，又查不出原因，再後來幹脆棄用該方法，自己實作一個copy方法，問題倒是再也沒有出現過。
昨天老闆同學又遇到這個問題，File#renameTo(File)方法在windows下面工作的好好的，在linux下偶爾又失靈了。回到家我掃了一遍JDK中File#renameTo(File)方法的源代碼，發現它調用的是一個本地的方法(native method)，無法再跟蹤下去。網上有人說該方法在window下是正常的，在linux下面是不正常的。這個很難說通，SUN不可能搞出這種平台不一緻的代碼出來啊。
後面在SUN的官方論壇上看到有人提到這個問題“works on windows, don't work on linux”，後面有人回複說是“file systems”不一樣。究竟怎麼不一樣呢？還是沒有想出來...
後面在一個論壇裡面發現了某人關于這個問題的闡述：
引用 In the Unix'esque O/S's you cannot renameTo() across file systems. This behavior is different than the Unix "mv" command. When crossing file systems mv does a copy and delete which is what you'll have to do if this is the case.
The same thing would happen on Windows if you tried to renameTo a different drive, i.e. C: -> D:
終于明白咯。
做個實驗：
Java代碼
- File sourceFile = new File("c:/test.txt");
- File targetFile1 = new File("e:/test.txt");
- File targetFile2 = new File("d:/test.txt");
- System.out.println("source file is exist? " + sourceFile.exists()
- + ", source file => " + sourceFile);
- System.out.println(targetFile1 + " is exist? " + targetFile1.exists());
- System.out.println("rename to " + targetFile1 + " => "
- + sourceFile.renameTo(targetFile1));
- System.out.println("source file is exist? " + sourceFile.exists()
- + ", source file => " + sourceFile);
- System.out.println(targetFile2 + " is exist? " + targetFile2.exists());
- System.out.println("rename to " + targetFile2 + " => "
- + sourceFile.renameTo(targetFile2));
File sourceFile = new File("c:/test.txt");
File targetFile1 = new File("e:/test.txt");
File targetFile2 = new File("d:/test.txt");
System.out.println("source file is exist? " + sourceFile.exists()
+ ", source file => " + sourceFile);
System.out.println(targetFile1 + " is exist? " + targetFile1.exists());
System.out.println("rename to " + targetFile1 + " => "
+ sourceFile.renameTo(targetFile1));
System.out.println("source file is exist? " + sourceFile.exists()
+ ", source file => " + sourceFile);
System.out.println(targetFile2 + " is exist? " + targetFile2.exists());
System.out.println("rename to " + targetFile2 + " => "
+ sourceFile.renameTo(targetFile2));
結果：
Java代碼
- source file is exist? true, source file => c:\test.txt
- e:\test.txt is exist? false
- rename to e:\test.txt => false
- source file is exist? true, source file => c:\test.txt
- d:\test.txt is exist? false
- rename to d:\test.txt => true
source file is exist? true, source file => c:\test.txt
e:\test.txt is exist? false
rename to e:\test.txt => false
source file is exist? true, source file => c:\test.txt
d:\test.txt is exist? false
rename to d:\test.txt => true
注意看結果，從C槽到E盤失敗了，從C槽到D盤成功了。因為我的電腦C、D兩個盤是NTFS格式的，而E盤是FAT32格式的。是以從C到E就是上面文章所說的"file systems"不一樣。從C到D由于同是NTFS檔案系統，是以不存在這個問題，當然就成功了。
果然是不能把File#renameTo(File)當作move方法使用。
可以考慮使用apache組織的commons-io包裡面的FileUtils#copyFile(File,File)和FileUtils#copyFileToDirectory(File,File)方法實作copy的效果。至于删除嘛，我想如果要求不是那麼精确，可以調用File#deleteOnExit()方法，在虛拟機終止的時候，删除掉這個目錄或檔案。