java - Files.delete 和 Files.deleteIfExists 的行为有点奇怪

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); }
    });

在调用删除方法后，我的空目录被锁定(在调用后立即检查它)，但直到应用程序关闭后才被删除。我觉得有点奇怪，但想知道为什么会发生这种情况。

(我使用 Windows 10)

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，所以 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，这种预检查是浪费的，当所有 move 操作成功时就不需要了。但是如果其他应用程序同时插入一个新文件，则不能保证它不会在您的Files.list(folderPath).count() == 0之间发生检查和后续的 deleteIfExists 调用。

更简洁的解决方案是记住移动何时失败。当没有移动失败时，仍然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); }
});