我用login.jsp进行登录留言板的管理页面用一个servlet进行身份验证。成功----->通过request.getRequestDispatcher("/admin/secure/manage?q=list").forward(request, response);return;其中/admin/secure/manage是ManageServlet的映射路径。来登录到manage的管理程序中，也就是ManageServlet来执行q=list的操作。然后转向到list.jsp中。

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ManageServlet的代码是：

package com.v512.servlet;

import java.io.IOException;

import java.util.List;

import javax.servlet.ServletException;

import javax.servlet.http.HttpServlet;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;

import org.apache.commons.dbutils.handlers.BeanListHandler;

import com.v512.Guestbook;

import com.v512.dbutil.OracleUtil;

public class ManageServlet extends HttpServlet {

private static final long serialVersionUID = -7850908097407733668L;

public void update(HttpServletRequest request, HttpServletResponse response)

throws ServletException, IOException {

String sql = "update guestbook set name=?,email=?,phone=?,title=?,content=? where id=?";

String message = "";

String param[] = { request.getParameter("name"),

request.getParameter("email"), request.getParameter("phone"),

request.getParameter("title"), request.getParameter("content"),

request.getParameter("id") };

OracleUtil db = new OracleUtil("java:/comp/env/jdbc/oracleds");

db.init();

int i = db.update(sql, param);

if (i == 1) {

message = "更新成功！";

request.setAttribute("guestbook.admin.update.message", message);

request.getRequestDispatcher("/admin/secure/list.jsp").forward(

request, response);

Guestbook gb = new Guestbook();

gb.setName(request.getParameter("name"));

gb.setEmail(request.getParameter("email"));

gb.setPhone(request.getParameter("phone"));

gb.setTitle(request.getParameter("title"));

gb.setContent(request.getParameter("content"));

request.setAttribute("admin/secure/update", gb);

} else {

message = "更新不成功！";

request.setAttribute("guestbook.admin.update.message", message);

request.getRequestDispatcher("/admin/secure/update.jsp").forward(

request, response);

}

}

public void delete(HttpServletRequest request, HttpServletResponse response)

throws ServletException, IOException {

String sql = "delete from guestbook where id=?";

String message = "";

String[] param = { request.getParameter("id") };

OracleUtil db = new OracleUtil("java:/comp/env/jdbc/oracleds");

db.init();

int i = db.update(sql, param);

if (i == 1) {

message = "删除成功！";

request.setAttribute("guestbook.admindelete.message", message);

request.getRequestDispatcher("/admin/secure/delete.jsp").forward(

request, response);

} else {

message = "删除不成功！";

request.setAttribute("guestbook.admin.delete.message", message);

request.getRequestDispatcher("/admin/secure/delete.jsp").forward(

request, response);

}

}

public void edit(HttpServletRequest request, HttpServletResponse response)

throws ServletException, IOException {

String sql = "select * from guestbook where id=?";

String[] param = { request.getParameter("id") };

OracleUtil db = new OracleUtil("java:/comp/env/jdbc/oracleds");

db.init();

List list = (List) db.query(sql, param, new BeanListHandler(

Guestbook.class));

request.setAttribute("guestbook.admin.edit", list.get(0));

request.getRequestDispatcher("http://www.v512.com").forward(request,

response);

}

public void list(HttpServletRequest request, HttpServletResponse response)

throws ServletException, IOException {

String sql = "select id ,name,title from guestbook order by id desc";

OracleUtil db = new OracleUtil("java:/comp/env/jdbc/oracleds");

db.init();

List list = (List) db.query(sql, null, new BeanListHandler(

Guestbook.class));

request.setAttribute("guestbook.admin.list", list);

request.getRequestDispatcher("/admin/secure/list.jsp").forward(request,

response);

return;

}

public void doGet(HttpServletRequest request, HttpServletResponse response)

throws ServletException, IOException {

String method = request.getParameter("q");

if (method.equals(null)) {

method = "list";

}

if (method.equals("edit")) {

edit(request, response);

} else if (method.equals("delete")) {

delete(request, response);

} else if (method.equals("update")) {

update(request, response);

} else {

list(request, response);

}

}

public void doPost(HttpServletRequest request, HttpServletResponse response)

throws ServletException, IOException {

doGet(request, response);

}

} ---------------------------------------------------------------------------------

可是我的前二次转向已经成功了！就是由

request.getRequestDispatcher("/admin/secure/manage?q=list").forward(request, response);

return; //这行代码的执行是以身份通过为前提的。其中/admin/secure/manage是ManageServlet的映射路径。

request.getRequestDispatcher("/admin/secure/list.jsp").forward(request, response);

return;然后它可以成功的转向到list.jsp;在list.jsp中又有两个链接如下：

编辑

删除

当点击“编辑”或“删除”时就出现了下面的异常：

java.lang.IllegalStateException: Cannot forward after response has been committed

com.v512.servlet.ManageServlet.edit(ManageServlet.java:73)