Question

我正在使用NIO文件频道管理文件并锁定它们。到目前为止它仍然有效，但是当我使用NIO文件锁锁定文件时，它会锁定文件，因此无法更改文件内容。例如，如果我尝试在记事本上编辑文本文件，它将显示以下错误消息： File Lock

这是预期的结果，但是如果我尝试从Windows资源管理器中删除该文件（我没有在其他操作系统上测试过可能也是可能的话）它会允许我，这是不受欢迎的，我想知道是否可以打开文件句柄

使用的代码：

private static final byte[] MessageBytes;
static {
    byte tmp[];
    try {
        tmp = "Hello World".getBytes("UTF-8");
    } catch (UnsupportedEncodingException ex) {
        //if fail get the bytes in whatever the java VM charset sets as default
        tmp = "Hello World".getBytes();
    }
    MessageBytes = tmp;
}
private static final String Filename = "Lock_test.txt";

 private static void createFileandLock() {
    Path FilePath = Paths.get(Filename);
    FileChannel OpenFCh;
    try {
        OpenFCh = FileChannel.open(FilePath, StandardOpenOption.CREATE,
                StandardOpenOption.READ, StandardOpenOption.WRITE
        //                    ,StandardOpenOption.APPEND
        );
        System.out.println("File Channel is Open.");
    } catch (IOException err) {
        OpenFCh = null;
    }
    if (OpenFCh != null) {
        FileLock Lock = null;
        try {
            Lock = OpenFCh.lock();
        } catch (IOException err) {
            System.out.println("Unable To Lock the File.");
        }
        try {
            OpenFCh.write(ByteBuffer.wrap(MessageBytes));
            OpenFCh.force(false);
            System.out.println("Message Recorded");
        } catch (IOException ex) {
            System.out.println("Unable To write data into file");
        }
        try {
            // at this point file still locked and open.
            //lets wait for input and meanwhile ask to delete the file. 
            System.out.print("Please Try to delete file at: ");
            System.out.println(FilePath.toString());
            System.out.println("Press Enter to Continue");
            System.in.read();
        } catch (IOException ex) {
        }
        if (Lock != null) {
            try {
                Lock.close();
            } catch (IOException ex) {
            }
        }
        try {
            OpenFCh.close();
        } catch (IOException ex) {
        }
    }
}

经过进一步研究后，我注意到使用RandomAccessFile将锁定文件以避免删除，因为它会创建一个基本上在下划线操作系统上打开句柄的File Descriptor。因此，使用RAF确实可以提供所需的结果： File Open Message

使用的代码：

private static void createRAFileandLock() {
    RandomAccessFile RAf;
    try {
        RAf = new RandomAccessFile(Filename, "rw");
    } catch (FileNotFoundException ex) {
        //since is open as RW shold not trigger.
        RAf = null;
    }
    if (RAf != null) {
        FileChannel OpenFCh = RAf.getChannel();
        FileLock Lock = null;
        try {
            Lock = OpenFCh.lock();
        } catch (IOException err) {
            System.out.println("Unable To Lock the File.");
        }
        try {
            OpenFCh.write(ByteBuffer.wrap(MessageBytes));
            OpenFCh.force(false);
            System.out.println("Message Recorded");
        } catch (IOException ex) {
            System.out.println("Unable To write data into file");
        }
         // at this point file still locked and open.
        //lets wait for input and meanwhile ask to delete the file. 
        try {
            System.out.print("Please Try to delete file at: ");
            System.out.println(Filename);
            System.out.println("Press Enter to Continue");
            System.in.read();
        } catch (IOException ex) {
        }
        if (Lock != null) {
            try {
                Lock.close();
            } catch (IOException ex) {
            }
        }
        try {
            OpenFCh.close();
            RAf.close();
        } catch (IOException ex) {
        }
    }
}

但是我想知道是否可以仅使用NIO存档。由于随机访问文件在IO包上。

Answer 1

未指定FileLock以防止删除。它仅指定与其他文件锁进行交互，因此您已经深入了解与平台相关的行为。如果RandomAccessFile以某种方式做你想要的东西，你可能会坚持下去，但你不能依赖它。

NB当然，FileChannel.open（）使用FileDescriptor，句柄等。

如何锁定文件以避免使用NIO包删除

1 个答案: