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 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());
        }

      }
    }
  }
}

防止listFiles()函数的nullpointerexception，并递归地从子目录中获取所有文件。

 public void listFilesForFolder(final File folder,List<File> fileList) {
    File[] filesInFolder = folder.listFiles();
    if (filesInFolder != null) {
        for (final File fileEntry : filesInFolder) {
            if (fileEntry.isDirectory()) {
            listFilesForFolder(fileEntry,fileList);
        } else {
            fileList.add(fileEntry);
        }
     }
    }
 }

 List<File> fileList = new List<File>();
 final File folder = new File("/home/you/Desktop");
 listFilesForFolder(folder);

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");

public static List<File> files(String dirname) {
    if (dirname == null) {
        return Collections.emptyList();
    }

    File dir = new File(dirname);
    if (!dir.exists()) {
        return Collections.emptyList();
    }

    if (!dir.isDirectory()) {
        return Collections.singletonList(file(dirname));
    }

    return Arrays.stream(Objects.requireNonNull(dir.listFiles()))
        .collect(Collectors.toList());
}

您可以将文件路径设置为参数，并创建包含所有文件路径的列表，而不必手动将其放入列表中。然后使用for循环和读取器。txt文件示例:

public static void main(String[] args) throws IOException{    
File[] files = new File(args[0].replace("\\", "\\\\")).listFiles(new FilenameFilter() { @Override public boolean accept(File dir, String name) { return name.endsWith(".txt"); } });
    ArrayList<String> filedir = new ArrayList<String>();
    String FILE_TEST = null;
    for (i=0; i<files.length; i++){
            filedir.add(files[i].toString());
            CSV_FILE_TEST=filedir.get(i) 

        try(Reader testreader = Files.newBufferedReader(Paths.get(FILE_TEST));
            ){
              //write your stuff
                 }}}