java - 全局理解

Question

我需要使用以下选项/参数在 java 中开发一个文件扫描器:

1. 一个目录
2. 一个或多个模式，如 *.xml、*.txt、*test.csv
3. 切换递归扫描

我认为最好的方法是这样的:

public class FileScanningTest {

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

        String directory = "C:\\tmp\\scanning\\";
        String glob      = "**/*.xml";
        Boolean rekursiv = false;

        final PathMatcher pathMatcher = FileSystems.getDefault().getPathMatcher("glob:"+glob);

        Files.walkFileTree(Paths.get(directory), new SimpleFileVisitor<Path>() {

            @Override
            public FileVisitResult visitFile(Path path, BasicFileAttributes attrs) throws IOException {
                if (pathMatcher.matches(path)) {
                    System.out.println(path);
                } 
                return FileVisitResult.CONTINUE;
            }

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

    }

}

我不明白为什么我必须在实际模式前加上“**/”。这也确实使扫描递归。如果我删除 **/，应用程序将不会再找到任何东西。

https://docs.oracle.com/javase/tutorial/essential/io/fileOps.html#glob告诉我 ** 表示递归，但为什么如果我删除它就不起作用？

有人可以给我提示吗？

谢谢大家，周末愉快

Answer 1

要使用从目录 /tmp/scanning/ 开始的 glob 递归查找 *.xml，请查看此示例。它与 Linux Ubuntu 一起工作，可以做你想做的事。它的工作方式类似于 Unix 查找实用程序。我没有在 Ubuntu 以外的其他操作系统上测试它，但你应该只需要更改文件名分隔符。

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.*;


public class FileScanningTest {

    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;
        }
    }


    public static void main(String[] args)
            throws IOException {
        boolean recursive = false;
        Path startingDir = Paths.get("/tmp/scanning");
        String pattern = "*.{html,xml}";

        Finder finder = new Finder(pattern);
        if (!recursive) {
            Path dir = startingDir;
            List<File> files = new ArrayList<>();
            try (DirectoryStream<Path> stream = Files.newDirectoryStream(dir, "*.{xml,html}")) {
                for (Path entry : stream) {
                    files.add(entry.toFile());
                }

                for (File xmlfile : files) {
                    System.out.println(xmlfile);
                }
            } catch (IOException x) {
                throw new RuntimeException(String.format("error reading folder %s: %s",
                        dir,
                        x.getMessage()),
                        x);
            }
        } else {    
            Files.walkFileTree(startingDir, finder);
            finder.done();
        }

    }
}

测试

 ~> java FileScanningTest
/tmp/scanning/dir2/test2.xml
/tmp/scanning/blah.xml
Matched: 2

如果你想匹配*.xml或test3.html，那么你可以使用这个模式:String pattern = "{*.xml, test3.html}";