模仿 chmod -R 755 的 java walkFileTree 不起作用

Question

我想确保目录树中的正确权限(目录为 0755，文件为 644)。这是我的类(class):

package NRF_Utils;

import java.io.IOException;
import java.nio.file.FileVisitResult;
import static java.nio.file.FileVisitResult.*;
import java.nio.file.FileVisitor;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.util.Set;
import java.util.logging.Logger;
import java.nio.file.attribute.BasicFileAttributes;
import java.nio.file.attribute.PosixFilePermission;
import java.nio.file.attribute.PosixFilePermissions;

public class DirectoryTreeOperations {
    private static final Logger log = Logger.getLogger("spv." + DirectoryTreeOperations.class.getName());

    public static boolean setPermissions(String root, String directoryPermissions, String filePermissions) {
        boolean result = true;
        //declaring the path to delete
        final Path path = Paths.get(root);
        final Set<PosixFilePermission> dirPermissions = PosixFilePermissions.fromString(directoryPermissions);
        final Set<PosixFilePermission> filPermissions = PosixFilePermissions.fromString(filePermissions);

        try {
            Files.walkFileTree(path, new FileVisitor<Path>() {

                @Override
                public FileVisitResult preVisitDirectory(Path dir,
                        BasicFileAttributes attrs) throws IOException {
                    System.out.println("setting dir permission on " + dir);
                    Files.setPosixFilePermissions(dir, dirPermissions);                 
                    return CONTINUE;
                }

                @Override
                public FileVisitResult visitFile(Path file,
                        BasicFileAttributes attrs) throws IOException {
                    System.out.println("setting file permission on " + file);
                    Files.setPosixFilePermissions(file, filPermissions);
                    return CONTINUE;
                }

                @Override
                public FileVisitResult visitFileFailed(Path file, IOException exc)
                        throws IOException {
                    log.severe("visitFileFailed failed on " + file + " : " + exc);
                    return CONTINUE;
                }

                @Override
                public FileVisitResult postVisitDirectory(Path dir,
                        IOException exc) throws IOException {
                    return CONTINUE;
                }

            });
        } catch (IOException e) {
            log.severe("setPermissions failed " + e);
            result = false;
        }
        return result;
    }

    // TODO remove and provide a proper unit test
    public static void main(String [] arg) {
        System.out.println ("setPermissions returned: " + setPermissions("/tmp/x", "rwxr-xr-x", "rw-r--r--"));
    }
}

为了进行测试，我做了:

mkdir -p /tmp/x/y/z;touch /tmp/x/y/z/f;chmod 000 /tmp/x/y/z

输出是:

setting dir permission on /tmp/x
setting dir permission on /tmp/x/y
setPermissions returned: true
nov. 26, 2017 2:45:00 PM NRF_Utils.DirectoryTreeOperations$1 visitFileFailed
GRAVE: visitFileFailed failed on /tmp/x/y/z : java.nio.file.AccessDeniedException: /tmp/x/y/z

java似乎不想探索目录树，因为权限不对，但我的目的是探索目录树以修复权限。 API 疯了吗？

Answer 1

它的这种行为方式看起来确实很奇怪，所以也许不是一个疯狂的 API，但实现肯定不适合使用 preVisitDirectory() 使目录可访问的特定情况。

Files.walkFileTree() 文档说:

Where the file is a directory, and the directory could not be opened, then the visitFileFailed method is invoked with the I/O exception, after which, the file tree walk continues, by default, at the next sibling of the directory.

并查看实现，它实际上在调用 visitor.preVisitDirectory() 之前尝试打开目录，这解释了您遇到的问题。

作为解决方案，您可以获取 FileTreeWalker.java 源代码，并在您自己的本地版本的 FileTreeWalker 中进行细微调整 - 直接查找对 visitor.preVisitDirectory() 的调用即可> 并将打开的目录代码移到之后发生。然后将您的代码更改为:

  new FileTreeWalker(EnumSet.noneOf(FileVisitOption.class), new FileVisitor<Path>() {
     ...
  }, Integer.MAX_VALUE).walk(path);

当你运行时，你会得到:

setting dir permission on /tmp/x
setting dir permission on /tmp/x/y
setting dir permission on /tmp/x/y/z
setting file permission on /tmp/x/y/z/f
setPermissions returned: true

这表明您对 FileVisitor 的实现没有问题。

希望对您有所帮助。