Files.delete 和 Files.deleteIfExists 有点奇怪的行为

Question

我得到这样的代码：

paths.forEach(folderPath -> {
        Path to = folderPath.getRoot().resolve(folderPath.getParent().subpath(0, folderPath.getNameCount() - 1)); // До имени (исключительно)
        try {
            Files.list(folderPath).forEach(filePath -> {
                try { Files.move(filePath, to.resolve(filePath.getFileName()), StandardCopyOption.ATOMIC_MOVE); }
                catch (IOException e) { processException(e); }
            });
            if (Files.list(folderPath).count() == 0)
                Files.deleteIfExists(folderPath); // this call
        } catch (IOException e) { processException(e); }
    });

调用删除方法后，我锁定了我的空目录（调用后立即检查），但直到应用程序关闭后才删除。我觉得有点奇怪，但想知道为什么会这样。

(我用Windows10)

Answer 1

来自 Files.list(Path) 的文档：

This method must be used within a try-with-resources statement or similar control structure to ensure that the stream's open directory is closed promptly after the stream's operations have completed.

您没有这样做，因此 Files.deleteIfExists(…) 的以下部分适用：

On some operating systems it may not be possible to remove a file when it is open and in use by this Java virtual machine or other programs.

你应该使用

paths.forEach(folderPath -> {
    Path to = folderPath.getParent();
    try {
        try(Stream<Path> files = Files.list(folderPath)) {
            files.forEach(filePath -> {
                try{Files.move(filePath, to.resolve(filePath.getFileName()), ATOMIC_MOVE);}
                catch (IOException e) { processException(e); }
            });
        }
        try {
            Files.deleteIfExists(folderPath);
        } catch(DirectoryNotEmptyException ex) {
            // may happen as you continue when Files.move fails,
            // but you already reported the original exception then
        }
    } catch (IOException e) { processException(e); }
});

这会在尝试删除目录之前关闭文件流。请注意，第二个流操作已被删除，这种预检查很浪费，当所有 move 操作成功时应该不需要。但是如果一些其他应用程序同时插入一个新文件，不能保证它不会在您的 Files.list(folderPath).count() == 0 检查和随后的 deleteIfExists 调用之间发生。

更简洁的解决方案是记住 move 失败的时间。当没有 move 失败时，仍不为空的目录应被视为错误情况，应像任何其他错误一样报告，例如

paths.forEach(folderPath -> {
    Path to = folderPath.getParent();
    try {
        boolean allMovesSucceeded;
        try(Stream<Path> files = Files.list(folderPath)) {
          allMovesSucceeded = files
            .map(filePath -> {
                try {
                    Files.move(filePath, to.resolve(filePath.getFileName()), ATOMIC_MOVE);
                    return true;
                }
                catch(IOException e) { processException(e); return false; }
            }).reduce(Boolean.TRUE, Boolean::logicalAnd);

        }
        if(allMovesSucceeded) Files.deleteIfExists(folderPath);
    } catch (IOException e) { processException(e); }
});

Files.delete 和 Files.deleteIfExists 有点奇怪的行为

A bit strange behaviour of Files.delete and Files.deleteIfExists

java

file-io

delete-file

nio2