菜品删除的提示框

我想如果删除的ID不存在的话，就弹出一个提示框，可是没有效果，怎么才能弹出呢

liqihang 2018-06-11

源自：项目：登录注册功能 5-2 作业题

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5回答

chrismorgen 2018-06-12 10:14:20

要将对msg的判断放到底部。
如下图所示。是msg="";而不是msg=" "；你的双引号中间多了一个空格符。修改完之后你需要的功能就完成了。祝学习愉快~

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提问者 liqihang 2018-06-12 09:45:09

<%@ page language="java" contentType="text/html; charset=utf-8"
    pageEncoding="utf-8"%>
<html>
<head>
<%String msg="";
if(request.getAttribute("msg")!=null)
msg=(String)request.getAttribute("msg"); %>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<script type="text/javascript">
    var msg="<%=msg%>";
if(msg!=null&&msg!=" "){
  alert(msg);
}
</script>
<title>菜品删除</title>
<style type="text/css">

</style>
</head>
<body>
<h3><%=msg %></h3>
<center>
  <h1>根据ID删除菜品</h1>
  <form action="/foodManage/deleteServlet" method="post">
   <table width="400px" border="1px" cellspacing="0px" cellpadding="0px">
    <tr>
     <td>菜品ID</td>
     <td><input type="text" name="id"></td>
    </tr>
    <tr>
     <td colspan="2" style="text-align:center"><input type="submit" value="删除"></td>
    </tr>
   </table>
  </form>
</center>
</body>

</html>

package foodServlet;

import java.io.IOException;
import java.util.Map;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import utils.FoodDaoImpl;

/**
*菜品删除的servlet
*/
@WebServlet("/deleteServlet")
public class deleteServlet extends HttpServlet {

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
   String id=request.getParameter("id");
   boolean flag=FoodDaoImpl.deleteFoodById(id);
   if(!flag){
    request.setAttribute("msg", "您要删除的菜品id不存在,请重新输入");
  request.getRequestDispatcher("/myFile.jsp/deleteById.jsp").forward(request, response);
    return;
}else{
  request.getRequestDispatcher("/myFile.jsp/showFoodList.jsp").forward(request, response);
}
}
  protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
  // TODO Auto-generated method stub
  doGet(request, response);
}

}

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chrismorgen 2018-06-11 17:59:44

你是放到代码底部了么？程序是按照顺序执行的。祝学习愉快~

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提问者 liqihang #1

放到后面也是这样，奇怪啊，

2018-06-11 20:22:43
chrismorgen 回复提问者 liqihang #2

你可以将你的代码粘贴上来方便我们检查。祝学习愉快~

2018-06-12 09:08:09
提问者 liqihang 回复 chrismorgen #3

菜品删除的jsp页面和servlet代码在上面贴出，请老师检阅。

2018-06-12 09:45:52