用RecyclerView 做瀑布流，item来回动？

用RecyclerView 做瀑布流， notifyDataSetChanged()之后，item来回动？
notify之后第一和第二个位置顶部有高度差

右边的item可能跑到左边

package com.oracle.servlet;

import java.io.IOException;
import java.util.List;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import com.oracle.domain.Book;
import com.oracle.domain.Category;
import com.oracle.service.BaseServlet;
import com.oracle.service.BookService;
import com.oracle.service.CategoryService;

public class BookServlet extends BaseServlet {
BookService bookService=new BookService();
public String findAll(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
List booklist = bookService.findAll();
request.setAttribute("booklist", booklist);
return "f:/jsps/book/list.jsp";
}
public String findByCid(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
String cid = request.getParameter("cid");
List booklist = bookService.findByCid(cid);
request.setAttribute("booklist", booklist);
return "f:/jsps/book/list.jsp";
}

public String findByBid(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {
    String bid = request.getParameter("bid");
     Book book = bookService.findByBid(bid);
     System.out.println(book);
    request.setAttribute("book", book);
    return "f:/jsps/book/desc.jsp";
}

}

不来回动怎么叫瀑布流？

网上有现成的例子，gradle的流行布局