虽然我同意Rich, Orian和其他人使用:

    final File keysFileFolder = new File(<path>); 
    File[] fileslist = keysFileFolder.listFiles();

    if(fileslist != null)
    {
        //Do your thing here...
    }

出于某种原因，这里所有的例子都使用绝对路径(即从根目录开始，或者，对于windows..)

我想补充的是，也可以使用相对路径。 所以，如果你的pwd(当前目录/文件夹)是folder1，你想要解析folder1/子文件夹，你只需写(在上面的代码中代替):

    final File keysFileFolder = new File("subfolder");

import java.io.File;


public class Test {

public void test1() {
    System.out.println("TEST 1");
}

public static void main(String[] args) throws SecurityException, ClassNotFoundException{

    File actual = new File("src");
    File list[] = actual.listFiles();
    for(int i=0; i<list.length; i++){
        String substring = list[i].getName().substring(0, list[i].getName().indexOf("."));
        if(list[i].isFile() && list[i].getName().contains(".java")){
                if(Class.forName(substring).getMethods()[0].getName().contains("main")){
                    System.out.println("CLASS NAME "+Class.forName(substring).getName());
                }

         }
    }

}
}

只要传递你的文件夹，它就会告诉你关于方法的主类。

这将读取指定路径下的指定文件扩展名文件(也可以查看子文件夹)

public static Map<String,List<File>> getFileNames(String 
dirName,Map<String,List<File>> filesContainer,final String fileExt){
    String dirPath = dirName;
    List<File>files = new ArrayList<>();
    Map<String,List<File>> completeFiles = filesContainer; 
    if(completeFiles == null) {
        completeFiles = new HashMap<>();
    }
    File file = new File(dirName);

    FileFilter fileFilter = new FileFilter() {
        @Override
        public boolean accept(File file) {
            boolean acceptFile = false;
            if(file.isDirectory()) {
                acceptFile = true;
            }else if (file.getName().toLowerCase().endsWith(fileExt))
              {
                acceptFile = true;
              }
            return acceptFile;
        }
    };
    for(File dirfile : file.listFiles(fileFilter)) {
        if(dirfile.isFile() && 
dirfile.getName().toLowerCase().endsWith(fileExt)) {
            files.add(dirfile);
        }else if(dirfile.isDirectory()) {
            if(!files.isEmpty()) {
                completeFiles.put(dirPath, files);  
            }

getFileNames(dirfile.getAbsolutePath(),completeFiles,fileExt);
        }
    }
    if(!files.isEmpty()) {
        completeFiles.put(dirPath, files);  
    }
    return completeFiles;
}

只需使用“文件”遍历所有“文件”。walkFileTree (java7)

Files.walkFileTree(Paths.get(dir), new SimpleFileVisitor<Path>() {
    @Override
    public FileVisitResult visitFile(Path file, BasicFileAttributes attrs) throws IOException {
        System.out.println("file: " + file);
        return FileVisitResult.CONTINUE;
    }
});

在Java 7及更高版本中，您可以使用listdir

Path dir = ...;
try (DirectoryStream<Path> stream = Files.newDirectoryStream(dir)) {
    for (Path file: stream) {
        System.out.println(file.getFileName());
    }
} catch (IOException | DirectoryIteratorException x) {
    // IOException can never be thrown by the iteration.
    // In this snippet, it can only be thrown by newDirectoryStream.
    System.err.println(x);
}

您还可以创建一个过滤器，然后将其传递给上面的newDirectoryStream方法

DirectoryStream.Filter<Path> filter = new DirectoryStream.Filter<Path>() {
    public boolean accept(Path file) throws IOException {
        try {
            return (Files.isRegularFile(path));
        } catch (IOException x) {
            // Failed to determine if it's a file.
            System.err.println(x);
            return false;
        }
    }
};

有关其他过滤示例，[参见文档]。(http://docs.oracle.com/javase/tutorial/essential/io/dirs.html#glob)

/**
 * Function to read all mp3 files from sdcard and store the details in an
 * ArrayList
 */


public ArrayList<HashMap<String, String>> getPlayList() 
    {
        ArrayList<HashMap<String, String>> songsList=new ArrayList<>();
        File home = new File(MEDIA_PATH);

        if (home.listFiles(new FileExtensionFilter()).length > 0) {
            for (File file : home.listFiles(new FileExtensionFilter())) {
                HashMap<String, String> song = new HashMap<String, String>();
                song.put(
                        "songTitle",
                        file.getName().substring(0,
                                (file.getName().length() - 4)));
                song.put("songPath", file.getPath());

                // Adding each song to SongList
                songsList.add(song);
            }
        }
        // return songs list array
        return songsList;
    }

    /**
     * Class to filter files which have a .mp3 extension
     * */
    class FileExtensionFilter implements FilenameFilter 
    {
        @Override
        public boolean accept(File dir, String name) {
            return (name.endsWith(".mp3") || name.endsWith(".MP3"));
        }
    }

你可以过滤任何文本文件或任何其他扩展..把它换成。mp3