1、创建SpacesItemDecoration辅助类

public class SpacesItemDecoration extends RecyclerView.ItemDecoration {
    private int space;
    public SpacesItemDecoration(int space) {
        this.space = space;
    }
    @Override
    public void getItemOffsets(Rect outRect, @NonNull View view, RecyclerView parent, @NonNull RecyclerView.State state) {
//        outRect.left = space;
//        outRect.right = space;
//        outRect.bottom = space;
          outRect.top = space;
        // Add top margin only for the first item to avoid double space between items
        if (parent.getChildLayoutPosition(view) == 0) {
            outRect.top = space;
        }
    }

    public static int px2dp(float dpValue) {
        return (int) (0.5f + dpValue * Resources.getSystem().getDisplayMetrics().density);
    }
}

2、使用SpacesItemDecoration辅助类

 RecyclerView.addItemDecoration(new SpacesItemDecoration(SpacesItemDecoration.px2dp(12)));