How to atomically rename a file in Java, even if the dest file already exists?

Question

I have a cluster of machines, each running a Java app.

These Java apps need to access a unique resource.txt file concurently.

I need to atomical

Answer 1

For Java 1.7+, use java.nio.file.Files.move(Path source, Path target, CopyOption... options) with CopyOptions "REPLACE_EXISTING" and "ATOMIC_MOVE".

See API documentation for more information.

For example:

Files.move(src, dst, StandardCopyOption.ATOMIC_MOVE);

Answer 2

I solve with a simple rename function.

Calling :

File newPath = new File("...");
newPath = checkName(newPath);
Files.copy(file.toPath(), newPath.toPath(), StandardCopyOption.REPLACE_EXISTING);

The checkName function checks if exits. If exits then concat a number between two bracket (1) to the end of the filename. Functions:

private static File checkName(File newPath) {
    if (Files.exists(newPath.toPath())) {

        String extractRegExSubStr = extractRegExSubStr(newPath.getName(), "\\([0-9]+\\)");
        if (extractRegExSubStr != null) {
            extractRegExSubStr = extractRegExSubStr.replaceAll("\\(|\\)", "");
            int parseInt = Integer.parseInt(extractRegExSubStr);
            int parseIntPLus = parseInt + 1;

            newPath = new File(newPath.getAbsolutePath().replace("(" + parseInt + ")", "(" + parseIntPLus + ")"));
            return checkName(newPath);
        } else {
            newPath = new File(newPath.getAbsolutePath().replace(".pdf", " (" + 1 + ").pdf"));
            return checkName(newPath);
        }

    }
    return newPath;

}

private static String extractRegExSubStr(String row, String patternStr) {
    Pattern pattern = Pattern.compile(patternStr);
    Matcher matcher = pattern.matcher(row);
    if (matcher.find()) {
        return matcher.group(0);
    }
    return null;
}

EDIT: Its only works for pdf. If you want other please replace the .pdf or create an extension paramter for it. NOTE: If the file contains additional numbers between brackets '(' then it may mess up your file names.