为什么Java 7 Files.walkFileTree在遇到远程驱动器上的tar文件时抛出异常

内容来源于 Stack Overflow,并遵循CC BY-SA 3.0许可协议进行翻译与使用

  • 回答 (2)
  • 关注 (0)
  • 查看 (228)

我使用Files.WalkFileTree()导航文件夹和计算音频文件,但遇到tar文件时出现问题,它似乎将其视为实际文件夹,我期待它跳过它。

我看不到任何让我控制此行为的选项

代码:

package com.jthink.songkong.fileloader;


import com.jthink.songkong.cmdline.SongKong;
import com.jthink.songkong.ui.MainWindow;

import java.nio.file.*;
import java.nio.file.attribute.BasicFileAttributes;
import java.util.concurrent.Callable;
import java.util.logging.Level;

/**
 * Count the number of files that can be loaded, for information purposes only
 */
public class CountFilesinFolder implements Callable<Boolean> {
    public static class CountFiles
            extends SimpleFileVisitor<Path> {
        private int fileCount = 0;
        private final PathMatcher matcher;

        CountFiles(String pattern) {
            matcher =
                    FileSystems.getDefault()
                            .getPathMatcher("regex:" + pattern);
        }

        /**
         * Find Music file
         *
         * @param file
         * @param attr
         * @return
         */
        @Override
        public FileVisitResult visitFile(Path file,
                                         BasicFileAttributes attr) {
            Path name = file.getFileName();
            if (name != null && matcher.matches(name)) {
                fileCount++;
            }
            return FileVisitResult.CONTINUE;
        }

        public int getFileCount() {
            return fileCount;
        }
    }


    private Path scanDir;
    public CountFilesinFolder(Path scanDir) {
        this.scanDir = scanDir;
    }

    public Boolean call() {
        CountFiles countFiles = null;
        try {
            countFiles = new CountFiles("^(?!._).*[.](?:mp3|mp4|m4p|m4b|m4a|ogg|flac|wma)$");
            Files.walkFileTree(scanDir, countFiles);
        }
        catch (Exception e) {
            MainWindow.logger.log(Level.SEVERE, "Unable to find file for deriving base folder", e);
        }
        MainWindow.logger.severe("Music File Count:"+countFiles.getFileCount());
        SongKong.setMaxProgress(countFiles.getFileCount());
        return true;
    }
}

给出了这个栈跟踪

java.nio.file.NoSuchFileException: Z:\Scratch\fred.tar
    at sun.nio.fs.WindowsException.translateToIOException(WindowsException.java:79)
    at sun.nio.fs.WindowsException.rethrowAsIOException(WindowsException.java:97)
    at sun.nio.fs.WindowsException.rethrowAsIOException(WindowsException.java:102)
    at sun.nio.fs.WindowsDirectoryStream.<init>(WindowsDirectoryStream.java:86)
    at sun.nio.fs.WindowsFileSystemProvider.newDirectoryStream(WindowsFileSystemProvider.java:526)
    at java.nio.file.Files.newDirectoryStream(Files.java:411)
    at java.nio.file.FileTreeWalker.walk(FileTreeWalker.java:179)
    at java.nio.file.FileTreeWalker.walk(FileTreeWalker.java:199)
    at java.nio.file.FileTreeWalker.walk(FileTreeWalker.java:69)
    at java.nio.file.Files.walkFileTree(Files.java:2591)
    at java.nio.file.Files.walkFileTree(Files.java:2624)
    at com.jthink.songkong.fileloader.CountFilesinFolder.call(CountFilesinFolder.java:68)
    at com.jthink.songkong.fileloader.CountFilesinFolder.call(CountFilesinFolder.java:15)
    at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:334)
    at java.util.concurrent.FutureTask.run(FutureTask.java:166)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1110)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:603)
    at java.lang.Thread.run(Thread.java:722)

但是这是一个远程驱动器(nas驱动器),本地驱动器上不会出现此类错误

编辑 基于以下答案,实施了以下我认为有效的答案

    @Override
            public FileVisitResult preVisitDirectory(Path dir, 
BasicFileAttributes attrs)
                    throws IOException {
                if(dir.endsWith(".tar"))
                {
                    return FileVisitResult.SKIP_SUBTREE;
                }
                return super.preVisitDirectory(dir, attrs);
            }

但我的测试是不对的,它实际上并不工作,因为FileTreeWalker中失败的代码在previsit方法之前调用

try {
            DirectoryStream<Path> stream = null;
            FileVisitResult result;

            // open the directory
            try {
                stream = Files.newDirectoryStream(file);
            } catch (IOException x) {
                return visitor.visitFileFailed(file, x);
            } catch (SecurityException x) {
                // ignore, as per spec
                return FileVisitResult.CONTINUE;
            }

            // the exception notified to the postVisitDirectory method
            IOException ioe = null;

            // invoke preVisitDirectory and then visit each entry
            try {
                result = visitor.preVisitDirectory(file, attrs);
                if (result != FileVisitResult.CONTINUE) {
                    return result;
                }
提问于
用户回答回答于

但实现visitFileFailed,你应该没问题。

public class MyFileVisitor extends SimpleFileVisitor<Path> {
    @Override
    public FileVisitResult visitFileFailed(Path file, IOException exc) throws IOException {
        if (file.toString().endsWith(".tar")) {
            return FileVisitResult.CONTINUE;
        }
        return super.visitFileFailed(file, exc);
    }
}

更新:如果我们仔细观察,我们可以看到walkFileTree使用Files.readAttributes 转向当前提供者:WindowsFileSystemProvider.readAttributes来确定路径是否为目录。

正如在评论中提到的人,我也不认为错误是在Java实现中,但是操作系统本地调用返回了错误的属性

如果你想为此做一个解决方法,一个选择是实现你自己的FileSystem,它透明地包装WindowsFileSystem实现,除了readAttributes返回.tar-paths作为文件而不是dir。

用户回答回答于

Tar档案可以被视为目录(文件包)。您可以通过preVisitDirectory在您的访问者中实现仅仅返回FileVisitResult.SKIP_SUBTREEtar档案的方法来防止这个错误:

public static class CountFiles
        extends SimpleFileVisitor<Path> {
    ...
    public FileVisitResult preVisitDirectory(Path dir, BasicFileAttributes attrs)
             throws IOException {
        if (dir.toString().toLowerCase().endsWith(".tar")) {
            return SKIP_SUBTREE;
        }
        return super.preVisitDirectory(dir, attrs);
    }
    ...
}

扫码关注云+社区

领取腾讯云代金券