static File mainFolder = new File("Folder");
    public static void main(String[] args) {

        lf.getFiles(lf.mainFolder);
    }
    public void getFiles(File f) {
        File files[];
        if (f.isFile()) {
            String name=f.getName();

        } else {
            files = f.listFiles();
            for (int i = 0; i < files.length; i++) {
                getFiles(files[i]);
            }
        }
    }

从Test文件夹中列出类路径内的文件

import java.io.File;
import java.io.IOException;

public class Hello {

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

        System.out.println("List down all the files present on the server directory");
        File file1 = new File("/prog/FileTest/src/Test");
        File[] files = file1.listFiles();
        if (null != files) {
            for (int fileIntList = 0; fileIntList < files.length; fileIntList++) {
                String ss = files[fileIntList].toString();
                if (null != ss && ss.length() > 0) {
                    System.out.println("File: " + (fileIntList + 1) + " :" + ss.substring(ss.lastIndexOf("\\") + 1, ss.length()));
                }
            }
        }


    }


}

import java.io.File;


public class ReadFilesFromFolder {
  public static File folder = new File("C:/Documents and Settings/My Documents/Downloads");
  static String temp = "";

  public static void main(String[] args) {
    // TODO Auto-generated method stub
    System.out.println("Reading files under the folder "+ folder.getAbsolutePath());
    listFilesForFolder(folder);
  }

  public static void listFilesForFolder(final File folder) {

    for (final File fileEntry : folder.listFiles()) {
      if (fileEntry.isDirectory()) {
        // System.out.println("Reading files under the folder "+folder.getAbsolutePath());
        listFilesForFolder(fileEntry);
      } else {
        if (fileEntry.isFile()) {
          temp = fileEntry.getName();
          if ((temp.substring(temp.lastIndexOf('.') + 1, temp.length()).toLowerCase()).equals("txt"))
            System.out.println("File= " + folder.getAbsolutePath()+ "\\" + fileEntry.getName());
        }

      }
    }
  }
}

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;
}

一个注释根据获得目录中的所有文件。 方法files .walk(path)将通过遍历以给定起始文件为根的文件树来返回所有文件。

例如，下面有一个文件树:

\---folder
    |   file1.txt
    |   file2.txt
    |
    \---subfolder
            file3.txt
            file4.txt

使用java.nio.file.Files.walk(路径):

Files.walk(Paths.get("folder"))
        .filter(Files::isRegularFile)
        .forEach(System.out::println);

给出如下结果:

folder\file1.txt
folder\file2.txt
folder\subfolder\file3.txt
folder\subfolder\file4.txt

要获取当前目录下的所有文件，请使用java.nio.file.Files.list(Path):

Files.list(Paths.get("folder"))
        .filter(Files::isRegularFile)
        .forEach(System.out::println);

结果:

folder\file1.txt
folder\file2.txt

上面有很多很好的答案，这里有一种不同的方法:在maven项目中，您放在resources文件夹中的所有内容都会默认复制到target/classes文件夹中。查看在运行时可用的内容

 ClassLoader contextClassLoader = 
 Thread.currentThread().getContextClassLoader();
    URL resource = contextClassLoader.getResource("");
    File file = new File(resource.toURI());
    File[] files = file.listFiles();
    for (File f : files) {
        System.out.println(f.getName());
    }

现在要从一个特定的文件夹中获取文件，假设你的资源文件夹中有一个名为“res”的文件夹，只需替换:

URL resource = contextClassLoader.getResource("res");

如果你想访问你的com.companyName包，那么:

contextClassLoader.getResource("com.companyName");