如何在 Java 7 中递归读取文件？

Question

我知道用于 Java 文件目录处理的 Apache Commons IO 库。不过，List all files from a directory recursively with Java 谈到了 Java 7 中的原生支持。

有没有人知道如何使用 Java 7 递归地列出/读取目录中的文件？

Answer 1

There's a tutorial on it。基本上，您实现了一个访问者，然后可以在进入、退出和遇到文件时调用它。支持确定文件是否是符号链接，以及遵循符号链接的选项（如果您愿意的话）。快速阅读一下 Java Paths 可能会有用，and the entire documentation starts here。

import static java.nio.file.FileVisitResult.*;

public static class PrintFiles
    extends SimpleFileVisitor<Path> {

    // Print information about
    // each type of file.
    @Override
    public FileVisitResult visitFile(Path file,
                                   BasicFileAttributes attr) {
        if (attr.isSymbolicLink()) {
            System.out.format("Symbolic link: %s ", file);
        } else if (attr.isRegularFile()) {
            System.out.format("Regular file: %s ", file);
        } else {
            System.out.format("Other: %s ", file);
        }
        System.out.println("(" + attr.size() + "bytes)");
        return CONTINUE;
    }

    // Print each directory visited.
    @Override
    public FileVisitResult postVisitDirectory(Path dir,
                                          IOException exc) {
        System.out.format("Directory: %s%n", dir);
        return CONTINUE;
    }

    // If there is some error accessing
    // the file, let the user know.
    // If you don't override this method
    // and an error occurs, an IOException 
    // is thrown.
    @Override
    public FileVisitResult visitFileFailed(Path file,
                                       IOException exc) {
        System.err.println(exc);
        return CONTINUE;
    }
}

说明文件遍历的第二个示例（来自 find 的 Java 实现）可以轻松修改为“匹配”所有文件。

/*
 * Copyright (c) 2009, Oracle and/or its affiliates. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 *   - Redistributions of source code must retain the above copyright
 *     notice, this list of conditions and the following disclaimer.
 *
 *   - Redistributions in binary form must reproduce the above copyright
 *     notice, this list of conditions and the following disclaimer in the
 *     documentation and/or other materials provided with the distribution.
 *
 *   - Neither the name of Oracle or the names of its
 *     contributors may be used to endorse or promote products derived
 *     from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
 * IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
 * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT OWNER OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
 * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
 * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

import java.io.*;
import java.nio.file.*;
import java.nio.file.attribute.*;
import static java.nio.file.FileVisitResult.*;
import static java.nio.file.FileVisitOption.*;
import java.util.*;

/**
 * Sample code that finds files that
 * match the specified glob pattern.
 * For more information on what
 * constitutes a glob pattern, see
 * http://docs.oracle.com/javase/javatutorials/tutorial/essential/io/fileOps.html#glob
 *
 * The file or directories that match
 * the pattern are printed to
 * standard out.  The number of
 * matches is also printed.
 *
 * When executing this application,
 * you must put the glob pattern
 * in quotes, so the shell will not
 * expand any wild cards:
 *     java Find . -name "*.java"
 */

public class Find {

    /**
     * A {@code FileVisitor} that finds
     * all files that match the
     * specified pattern.
     */
    public static class Finder
        extends SimpleFileVisitor<Path> {

        private final PathMatcher matcher;
        private int numMatches = 0;

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

        // Compares the glob pattern against
        // the file or directory name.
        void find(Path file) {
            Path name = file.getFileName();
            if (name != null && matcher.matches(name)) {
                numMatches++;
                System.out.println(file);
            }
        }

        // Prints the total number of
        // matches to standard out.
        void done() {
            System.out.println("Matched: "
                + numMatches);
        }

        // Invoke the pattern matching
        // method on each file.
        @Override
        public FileVisitResult
            visitFile(Path file,
                BasicFileAttributes attrs) {
            find(file);
            return CONTINUE;
        }

        // Invoke the pattern matching
        // method on each directory.
        @Override
        public FileVisitResult
            preVisitDirectory(Path dir,
                BasicFileAttributes attrs) {
            find(dir);
            return CONTINUE;
        }

        @Override
        public FileVisitResult
            visitFileFailed(Path file,
                IOException exc) {
            System.err.println(exc);
            return CONTINUE;
        }
    }

    static void usage() {
        System.err.println("java Find <path>" +
            " -name \"<glob_pattern>\"");
        System.exit(-1);
    }

    public static void main(String[] args)
        throws IOException {

        if (args.length < 3 
            || !args[1].equals("-name"))
            usage();

        Path startingDir = Paths.get(args[0]);
        String pattern = args[2];

        Finder finder = new Finder(pattern);
        Files.walkFileTree(startingDir, finder);
        finder.done();
    }
}

在我的系统（Linux / Fedora）上，它运行良好；然而，我只是在测试它的功能，并玩弄它。我没有对它的性能或任何其他有意义的测量进行压力测试（除了“它有效”）。

Answer 2

使用Files.walkFileTree。

（没有使用它的经验，但我只是在文档中找到了它，看起来使用起来很简单。）