File.delete（）不会删除文件

Question

There's something going on here that I don't understand. This code deletes all the files in the "stuff"directory:

public static void main(String[] args) throws Exception {

    File dire = new File("C:\\Users\\spacitron\\Desktop\\Stuff");

    for (File doc : dire.listFiles()) {
        doc.delete();
    }

}

However it won't work if I try to do something useful with it, such as only deleting duplicate files:

public static void main(String[] args) throws Exception {

    File dire = new File("C:\\Users\\spacitron\\Desktop\\Stuff");
    ArrayList<String> hashes = new ArrayList<>();
    for (File doc : dire.listFiles()) {
        String docHash = getHash(doc);
        if (hashes.contains(docHash)) {
            doc.delete();
        } else {
            hashes.add(docHash);
        }
    }

}

public static String getHash(File d) {
    MessageDigest md = null;
    try {
        md = MessageDigest.getInstance("SHA1");
        FileInputStream inStream = new FileInputStream(d);
        DigestInputStream dis = new DigestInputStream(inStream, md);
        BufferedInputStream bis = new BufferedInputStream(dis);
        while (true) {
            int b = bis.read();
            if (b == -1)
                break;
        }
    } catch (NoSuchAlgorithmException | IOException e) {
        e.printStackTrace();
    }

    BigInteger bi = new BigInteger(md.digest());

    return bi.toString(16);
}

What gives?

Answer 1

You need to close your input streams in a finally block would be best, These will be accessing you files still preventing them from being deleted as they are in use

    FileInputStream inStream = null;
    DigestInputStream dis = null;
    BufferedInputStream bis = null;

    try {
       md = MessageDigest.getInstance("SHA1");
       inStream = new FileInputStream(d);
       dis = new DigestInputStream(inStream, md);
       bis = new BufferedInputStream(dis);
       while (true) {
            int b = bis.read();
            if (b == -1)
                break;
            }
   } catch (NoSuchAlgorithmException | IOException e) {
       e.printStackTrace();
   } finally {
       try{
          if(inStream!= null)
              inStream.close();
          if(dis != null)
              dis.close();
          if(bis != null)
              bis.close()
      } catch (Exception ex){
          ex.printStackTrace()
      }         
    }

Answer 2

Windows does not permit deleting files that are open, unless they are opened with a special flag that is unavailable when programming in Java. While this code would work on a Unix system, on Windows it won't.

Closing open files is a good idea in general because operating systems impose a limit on the number of files that an application can have open at any given time.