response.sendRedirect("/a.jsp");

　　页面的路径是相对路径。sendRedirect可以将页面跳转到任何页面，不一定局限于本web应用中，如：

　　response.sendRedirect("URL");

　　跳转后浏览器地址栏变化。

　　这种方式要传值出去的话，只能在url中带parameter或者放在session中，无法使用request.setAttribute来传递。

　　2) forward方式

　　RequestDispatcher dispatcher = request.getRequestDispatcher("/a.jsp");

　　dispatcher .forward(request, response);

　　Servlet页面跳转的路径是相对路径。forward方式只能跳转到本web应用中的页面上。

　　跳转后浏览器地址栏不会变化。

　　使用这种方式跳转，传值可以使用三种方法：url中带parameter，session，request.setAttribute

实例：

第一种方法:

AccountBean.java文件

package com.ht.servlet;

public class AccountBean {
 private String username = "";
 private String password = "";
 public String getPassword() {
  return password;
 }
 public void setPassword(String password) {
  this.password = password;
 }
 public String getUsername() {
  return username;
 }
 public void setUsername(String username) {
  this.username = username;
 }
}

CheckAccount.java文件

package com.ht.servlet;

import java.io.IOException;

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

public class CheckAccount extends HttpServlet {

 @Override
 protected void doPost(HttpServletRequest req, HttpServletResponse resp)
   throws ServletException, IOException {
  doGet(req,resp);
 }

 @Override
 public void doGet(HttpServletRequest req, HttpServletResponse resp)
   throws ServletException, IOException {
  HttpSession session = req.getSession();
  AccountBean account = new AccountBean();
  String username = req.getParameter("username");
  String pwd = req.getParameter("pwd");
  account.setPassword(pwd);
  account.setUsername(username);
  if((username != null)&&(username.trim().equals("jsp"))) {
   if((pwd != null)&&(pwd.trim().equals("1"))) {
    System.out.println("success");
    session.setAttribute("account", account);
    String login_suc = "success.jsp";
    resp.sendRedirect(login_suc);
    return;
   }
  }
  String login_fail = "fail.jsp";
  resp.sendRedirect(login_fail);
  return;
 }
 
}

第二种方法：
package servlets;

import java.io.IOException;
import java.io.PrintWriter;

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

public class LoginServlet extends HttpServlet {

 
 public void doGet(HttpServletRequest request, HttpServletResponse response)
   throws ServletException, IOException {

  doPost(request,response);
 }

 public void doPost(HttpServletRequest request, HttpServletResponse response)
   throws ServletException, IOException {

  String user = request.getParameter("user");
  RequestDispatcher rd = null;
  if(user!=null&&user.equals("admin"))
  {
   request.getSession().setAttribute("login", "true");
   rd = request.getRequestDispatcher("admin.html");
   rd.forward(request, response);  
  }
  else if(user!=null&&user.equals("common"))
  {
   request.getSession().setAttribute("login", "true");
   rd = request.getRequestDispatcher("common.html");
   rd.forward(request, response);    
  }
  else
   response.sendRedirect("login.html");
 }

}