页面重定向问题（Serlvet负责逻辑运算，jsp负责输入输出）：传递表单数据到Serlvet，然后在Serlvet中将接收的表单数据去计算它的字符长度，在页面重定向时作为页面welcome.jsp的请求参数，由welcome.jsp负责显示。仔细阅读下列程序：input.jsp:

Output.java:import java.io.IOException;import javax.servlet.ServletException;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;public class Output extends HttpServlet {private static final long serialVersionUID = 1L;public Output() {// TODO Auto-generated constructor stub}protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {String school=request.getParameter("schoolname");response.sendRedirect("welcome.jsp?len="+len);}protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {}}welcome.jsp:输出长度值<%=request.getParameter("len") %>

A. len.length();
B. int schoollen=school.length();
C. int len = len.length();
D. int len = school.length();