Type mismatch: cannot convert from Object to Book

这是jsp的
<%
			 Book book = request.getAttribute("book");
			for(Student student:book.getStudents()){
		%>
			<tr>
				<td><a href="QueryStudentBySno?sno=<%= student.getSno()%>"><%= student.getSno()%></a></td>
				
				<td><%= student.getSname()%></td>
				<td><%= student.getSage()%></td>
				<td><a href="DeleteStudentServlet?sno=<%= student.getSno()%>">删除</a></td>
				
			</tr>
		<% 
			}
		 %>

	book.setStudents(students);
		request.setAttribute("book", book);
		request.getRequestDispatcher("index.jsp").forward(request, response);