下面是一个示例代码，演示如何从外部存储中列出图像，并使用RecyclerView显示它们：

1. 添加必要的权限到AndroidManifest.xml文件中：

2. 创建一个新的布局文件，用于显示每个图像的视图。例如，image_item.xml：

3. 创建一个新的适配器类，用于将图像列表绑定到RecyclerView。例如，ImageAdapter.java：

public class ImageAdapter extends RecyclerView.Adapter {

    private List imagePaths;

    public ImageAdapter(List imagePaths) {
        this.imagePaths = imagePaths;
    }

    @NonNull
    @Override
    public ImageViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.image_item, parent, false);
        return new ImageViewHolder(view);
    }

    @Override
    public void onBindViewHolder(@NonNull ImageViewHolder holder, int position) {
        String imagePath = imagePaths.get(position);
        Bitmap bitmap = BitmapFactory.decodeFile(imagePath);
        holder.imageView.setImageBitmap(bitmap);
    }

    @Override
    public int getItemCount() {
        return imagePaths.size();
    }

    public static class ImageViewHolder extends RecyclerView.ViewHolder {
        ImageView imageView;

        public ImageViewHolder(View itemView) {
            super(itemView);
            imageView = itemView.findViewById(R.id.imageView);
        }
    }
}

4. 在你的Activity中，获取外部存储中的图像路径，并将其传递给适配器。例如，MainActivity.java：

public class MainActivity extends AppCompatActivity {

    private RecyclerView recyclerView;
    private ImageAdapter adapter;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        recyclerView = findViewById(R.id.recyclerView);
        recyclerView.setLayoutManager(new GridLayoutManager(this, 2));

        List imagePaths = getImagePathsFromExternalStorage();
        adapter = new ImageAdapter(imagePaths);
        recyclerView.setAdapter(adapter);
    }

    private List getImagePathsFromExternalStorage() {
        List imagePaths = new ArrayList<>();

        String path = Environment.getExternalStorageDirectory().getAbsolutePath() + "/Pictures";
        File directory = new File(path);
        File[] files = directory.listFiles();

        if (files != null) {
            for (File file : files) {
                if (file.isFile() && file.getName().endsWith(".jpg")) {
                    imagePaths.add(file.getAbsolutePath());
                }
            }
        }

        return imagePaths;
    }
}

这个示例假设图像位于外部存储的"Pictures"目录中，且文件类型为.jpg。你可以根据自己的需求进行修改。