How to open file in shared mode in Java

Question

How to open file in shared mode in Java to allow other users to read and modify the file?

Thanks

Answer 1

In case you're asking about the Windows platform, where files are locked at filesystem level, here's how to do it with Java NIO:

    Files.newInputStream(path, StandardOpenOption.READ)

And a demonstration that it actually works:

    File file = new File("<some existing file>");
    try (InputStream in = Files.newInputStream(file.toPath(), StandardOpenOption.READ)) {
        System.out.println(file.renameTo(new File("<some other name>"));
    }

Will print true, because a file open in shared-read mode may be moved.

For more details refer to java.nio.file.StandardOpenOption.

Answer 2

I'm not entirely sure I know what you mean, but if you mean concurrent modification of the file, that is not a simple process. Actually, it's pretty involved and there's no simple way to do that, off the top of my head you'd have to:

• Decide whether the file gets refreshed for every user when someone else modifies it, losing all changes or what to do in that case;
• Handle diffing & merging, if necessary;
• Handle synchronization for concurrent writing to the same file, so that when two users want to write that file, the content doesn't end up gibberishly, e.g., if one user wants to write "foo" and another one wants to write "bar", the content might end up being "fbaroo" without synchronization.

If you just want to open a file in read-only mode, all you gotta do is open it via FileInputStream or something similar, an object that only permits reading operations.