用于跟踪Java中文件更改的文件ID? [英] File id for keeping track of file changes in Java?

问题描述

我试图找到一种跟踪文件的方法，即使它们在文件系统中被移动或重命名.

I'm trying to find a way to keep track of files even when they are moved or renamed in the file system.

我想到的一个想法是在Java 7中使用新的UserDefinedFileAttributeView并创建一个自定义文件属性作为一种自定义ID.我认为这可能适用于不同的平台(主要是Windows和Mac).但是我无法使它正常工作.甚至在此页面上尝试该示例时，这行:

One idea I had was to use the new UserDefinedFileAttributeView in Java 7 and create a custom file attribute as a sort of custom id. I thought that this might work on different platforms (Windows and Mac primarily). But I can't get it to work. Even trying the example on this page, when I get to this line:

UserDefinedFileAttributeView view = Files.getFileAttributeView(file, UserDefinedFileAttributeView.class);

我只为view变量获取了一个空值，然后程序由于空指针异常而停止了.

I only get a null value for the view variable, and then the program stops with a nullpointer exception.

然后，我发现至少有一种针对Mac的方法可能更简单:使用BasicFileAttributes fileKey属性.我试过了，即使我移动文件或重命名文件，fileKey似乎也保持不变.但是，它也表示此功能取决于平台，我记得在某处读到它在Windows上不起作用...

I then found that there is a perhaps easier way to do this for Mac at least: use the BasicFileAttributes fileKey attribute. I tried this, and the fileKey seems to stay the same even if I move the file or rename it. However, it also says that this functionality is platform dependent, and I remember reading somewhere that it doesn't work on Windows...

首先，在Mac上，fileKey方法是一种稳定的方法吗?如果是这样，对于Windows的相同功能我该怎么办?有人知道为什么我在UserDefinedFileAttributeView上获取null吗?因为我想，如果我能做到这一点应该是跨平台的.

So first of all, is the fileKey method a stable way of doing this on Mac? And if so, what can I do for the same functionality for Windows? Anyone know why I get null on the UserDefinedFileAttributeView? Because if I could get that to work it should be cross-platform I guess.

这不是需要超级鲁棒和可扩展的东西，它只是我正在开发的一个小助手应用程序，但是在移动或重命名文件时至少必须可靠地标识文件...

This is not something that needs to be super robust and scalable, it is just a small helper application I'm developing, but it needs to be at least reliable in identifying files when moved or renamed...

推荐答案

我在Windows XP计算机上尝试了Oracle示例.该代码示例中有一个非常小的错误，但是除此之外，该代码还可以正常工作-至少在Windows XP上如此.希望它也可以在Linux等系统上运行，但我个人仅在Windows XP上进行过尝试.

I tried the Oracle example on a Windows XP computer. There was a very minor bug in the code example, but other than this, the code worked fine -- at least on Windows XP. Hopefully it would also work on Linux etc, but I personally have only tried it on Windows XP.

public static void main(String args[])
        throws Exception
{
    Path target = Paths.get("C:\\mytemp\\Something.txt");
    Files.createFile(target);
    UserDefinedFileAttributeView view = Files.getFileAttributeView(target, UserDefinedFileAttributeView.class);
    view.write("user.mimetype", Charset.defaultCharset().encode("text/html"));
    String name = "user.mimetype";
    ByteBuffer buf = ByteBuffer.allocate(view.size(name));
    view.read(name, buf);
    buf.flip();
    String value = Charset.defaultCharset().decode(buf).toString();
    System.out.println("value="+value);

只是确保不只是从视图中读取属性，我还使用第二个视图运行了相同的代码.这也起作用...

Just to be sure the attribute was not just being read from the view, I also ran the same code using a 2nd view. This also worked...

public static void main(String args[])
        throws Exception
{
    Path target = Paths.get("C:\\mytemp\\SomethingDifferent.txt");
    Files.createFile(target);
    UserDefinedFileAttributeView view = Files.getFileAttributeView(target, UserDefinedFileAttributeView.class);
    view.write("user.mimetype", Charset.defaultCharset().encode("text/html"));
    String name = "user.mimetype";

    UserDefinedFileAttributeView view2 = Files.getFileAttributeView(target, UserDefinedFileAttributeView.class);
    ByteBuffer buf = ByteBuffer.allocate(view2.size(name));
    view2.read(name, buf);
    buf.flip();
    String value = Charset.defaultCharset().decode(buf).toString();
    System.out.println("value="+value);


}

如果这样的自定义文件属性在所有主要平台上都可以使用，那就太好了，因为在某些情况下，这样的自定义文件属性非常有用.希望他们能做到.

It would be great if such custom file attributes work across all the major platforms, as such custom file attributes are incredibly handy in some situations. Hope they do.

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