请问不相同的key值，Map添加值的时候还是覆盖了？
web.xml
<?xml version="1.0" encoding="UTF-8"?> <web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" id="WebApp_ID" version="3.0"> <display-name>Libary</display-name> <welcome-file-list> <welcome-file>index.html</welcome-file> <welcome-file>index.htm</welcome-file> <welcome-file>index.jsp</welcome-file> <welcome-file>default.html</welcome-file> <welcome-file>default.htm</welcome-file> <welcome-file>default.jsp</welcome-file> </welcome-file-list> <servlet> <description></description> <display-name>InitServlet</display-name> <servlet-name>InitServlet</servlet-name> <servlet-class>Servlet.InitServlet</servlet-class> <load-on-startup>2</load-on-startup> </servlet> <servlet-mapping> <servlet-name>InitServlet</servlet-name> <url-pattern>/InitServlet</url-pattern> </servlet-mapping> <filter> <filter-name>OneFilter</filter-name> <filter-class>Filter.One</filter-class> <init-param> <param-name>charSet</param-name> <param-value>UTF-8</param-value> </init-param> </filter> <filter-mapping> <filter-name>OneFilter</filter-name> <url-pattern>/*</url-pattern> </filter-mapping> </web-app>
package Servlet;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import javax.servlet.ServletConfig;
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 User.User;
/**
* Servlet implementation class InitServlet
*/
public class InitServlet extends HttpServlet {
private static final long serialVersionUID = 1L;
@Override
public void init() throws ServletException {
// 创建一个User集合类用于保存用户集合
List<User> UserList = new ArrayList<User>();
// 将集合保存在ServletContext域中
this.getServletContext().setAttribute("list",UserList);
}
}package Servlet;
import java.io.IOException;
import java.util.List;
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 User.User;
/**
* Servlet implementation class RegistServlet
*/
@WebServlet("/RegistServlet")
public class RegistServlet extends HttpServlet {
private static final long serialVersionUID = 1L;
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
//获得注册页面的相关信息
String username = request.getParameter("username");
String password = request.getParameter("password");
String checkPWD = request.getParameter("checkPWD");
String phone = request.getParameter("phone");
String email = request.getParameter("email");
//进行后台验证 防止吊毛用户在前端删除验证方式
String usernameRegex = "[a-zA-Z_0-9]{6,12}";
boolean flag1 = username.matches(usernameRegex);
String passwordRegex = "[0-9]{6,12}";
boolean flag2 = password.matches(passwordRegex);
String phoneRegex = "1[34578][0-9]{9}";
boolean flag3 = phone.matches(phoneRegex);
String emailRegex = "[a-zA-Z_0-9]{6,}@([a-zA-Z]+ | \\d+)(\\.[a-zA-Z]+)+";
boolean flag4 = email.matches(emailRegex);
System.out.println(username);
System.out.println(password);
System.out.println(checkPWD);
System.out.println(phone);
System.out.println(email);
if(flag1==false && flag2==false && flag3==false && flag4==false) {
//不符合注册条件，进行重定向并且转发数据
response.sendRedirect(request.getContextPath()+"/regist.jsp?flag=1");
}else {
//将符合的信息存储在User中
User user = new User();
user.setUsername(username);
user.setPassword(password);
user.setEmail(email);
user.setPhone(phone);
// 将User存入集合中
List<User> UserList = (List<User>)this.getServletContext().getAttribute("list");
UserList.add(user);
this.getServletContext().setAttribute("UserList", UserList);
//然后进行页面跳转
response.sendRedirect(request.getContextPath()+"/index.jsp?flag=1");
}
}
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
doGet(request, response);
}
}package Servlet;
import java.io.IOException;
import java.util.HashMap;
import java.util.List;
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 User.User;
/**
* Servlet implementation class LoginServlet
*/
@WebServlet("/LoginServlet")
public class LoginServlet extends HttpServlet {
private static final long serialVersionUID = 1L;
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
String username = request.getParameter("username");
String password = request.getParameter("password");
//获得集合
List<User> UserList = (List<User>) this.getServletContext().getAttribute("UserList");
//判断
for(User u : UserList) {
if(u.getUsername().equals(username) && u.getPassword().equals(password)) {
//进行页面跳转
request.getSession().setAttribute("username", username);
response.sendRedirect(request.getContextPath()+"/server.jsp");
}else{
//页面跳转
}
}
}
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
doGet(request, response);
}
}package Servlet;
import java.io.IOException;
import java.util.HashMap;
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;
/**
* Servlet implementation class CatgoryServlet
*/
@WebServlet("/CatgoryServlet")
public class CatgoryServlet extends HttpServlet {
private static final long serialVersionUID = 1L;
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
String id = request.getParameter("id");
String catgoryName = request.getParameter("catgoryName");
String description = request.getParameter("description");
//创建Map集合来存储catgoryName key-id value-catgoryName
Map<String,String> map = new HashMap<String,String>();
map.put(id, catgoryName);
this.getServletContext().setAttribute("map", map);
Map<String,String> maps = (Map<String, String>) this.getServletContext().getAttribute("map");
for(String key : maps.keySet()) {
System.out.println(key+"==="+maps.get(key));
}
}
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// TODO Auto-generated method stub
doGet(request, response);
}
}<%@ page language="java" contentType="text/html; charset=UTF-8"
pageEncoding="UTF-8"%>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
String flag = request.getParameter("flag");
%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta charset="UTF-8">
<title>图书馆管理系统首页</title>
<script type="text/javascript">
var flag = <%=flag%>;
if(flag == 1){
alert("注册成功！");
}
</script>
</head>
<body>
<center>
<h1>登录 | <a href="<%=basePath%>regist.jsp">注册</a></h1>
<form action="<%=basePath%>/LoginServlet" method="post">
<table width="350px" cellspacing="0px" cellpadding="0px" border="1px">
<tr>
<td>用户名</td>
<td><input type="text" name="username" placeholder="用户名为3-12位字母数字或下划线组合" ></td>
</tr>
<tr>
<td>密 码</td>
<td><input type="password" name="password" placeholder="长度为6-12位的纯数字" ></td>
</tr>
<tr>
<td colspan="2" style="text-align:center">
<input type="submit" value="登录">
<input type="reset" value="取消">
</td>
</tr>
</table>
</form>
</center>
</body>
</html><%@ page language="java" contentType="text/html; charset=UTF-8"
pageEncoding="UTF-8"%>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
String flag = request.getParameter("flag");
%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta charset="UTF-8">
<title>用户注册</title>
</head>
<body>
<script type="text/javascript">
function mk(){
var id1 = document.getElementById("password").value;
var id2 = document.getElementById("password2").value;
if(id1==id2){
}else{
alert("两次密码不相同！");
}
}
var flag = <%=flag%>;
if(flag ==1 ){
alert("注册信息不正确！");
}
</script>
<center>
<h1>用户注册</h1>
<form action="<%=basePath%>RegistServlet" method="post">
<table width="400px" cellspacing="0px" cellpadding="0px" border="1px">
<tr>
<td>用户名</td>
<td><input type="text" name="username" placeholder="用户名为3-12位字母数字或下划线组合" pattern="[a-zA-Z_0-9]{3,12}"></td>
</tr>
<tr>
<td>密 码</td>
<td><input type="password" name="password" placeholder="密码长度为6-12位的纯数字" id="password" pattern="[0-9]{6,12}"></td>
</tr>
<tr>
<td>确认密码</td>
<td><input type="password" name="checkPWD" placeholder="密码长度为6-12位的纯数字" id="password2" pattern="[0-9]{6,12}"></td>
</tr>
<tr>
<td>手机号码</td>
<td><input type="text" name="phone" placeholder="请输入正确的手机号码格式" onclick="mk()" pattern="1[34578][0-9]{9}"></td>
</tr>
<tr>
<td>邮箱</td>
<td><input type="email" name="email" placeholder="请输入正确邮箱格式" required="required"></td>
</tr>
<tr>
<td colspan="2" style="text-align:center">
<input type="submit" value="注册">
<input type="reset" value="重置">
</td>
</tr>
</table>
</form>
</center>
</body>
</html><%@ page language="java" contentType="text/html; charset=UTF-8" pageEncoding="UTF-8"%> <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> <html> <head> <meta charset="UTF-8"> <title>图书后台管理系统</title> </head> <frameset rows="20%,*"> <frame src="./top.jsp"></frame> <frameset cols="10%,*"> <frame src="./left.jsp"></frame> <frame name="main"></frame> </frameset> </frameset> </html>
<%@ page language="java" contentType="text/html; charset=UTF-8"
pageEncoding="UTF-8"%>
<%
String name = (String)request.getSession().getAttribute("username");
%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta charset="UTF-8">
<title>Insert title here</title>
</head>
<body>
<center>
<h1>
图书后台管理系统<span style="font-size:12px">您好,<%=name %>
</h1>
</center>
</body>
</html><%@ page language="java" contentType="text/html; charset=UTF-8" pageEncoding="UTF-8"%> <% String path = request.getContextPath(); String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/"; %> <!DOCTYPE html> <html> <head> <meta charset="UTF-8"> <title>Insert title here</title> </head> <body> <p><a href="<%=basePath%>/catgory.jsp" target="main">分类添加</a></p> <p><a href="<%=basePath%>/addbook.jsp" target="main">图书添加</a></p> <p><a href="<%=basePath%>/show.jsp" target="main">图书查询</a></p> </body> </html>
<%@ page language="java" contentType="text/html; charset=UTF-8" pageEncoding="UTF-8"%> <% String path = request.getContextPath(); String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/"; %> <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> <html> <head> <meta charset="UTF-8"> <title>图书分类添加</title> </head> <body> <center> <h1>图书分类添加</h1> <form action="<%=basePath%>/CatgoryServlet" method="post"> <table width="400px" cellspacing="0px" cellpadding="0px" border="1px"> <tr> <td>分类ID</td> <td><input type="text" name="id"></td> </tr> <tr> <td>名 字</td> <td><input type="text" name="catgoryName"></td> </tr> <tr> <td>描 述</td> <td><input type="text" name="description"></td> </tr> <tr> <td colspan="2" style="text-align:center"> <input type="submit" value="添加"> <input type="reset" value="重置"> </td> </tr> </table> </form> </center> </body> </html>
<%@page import="java.util.Map"%>
<%@ page language="java" contentType="text/html; charset=UTF-8"
pageEncoding="UTF-8"%>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
Map<String,String> maps =(Map<String,String>) this.getServletContext().getAttribute("map");
%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta charset="UTF-8">
<title>图书添加</title>
</head>
<body>
<center>
<h1>图书添加</h1>
<form action="<%=basePath%>/AddBookServlet" method="post">
<table width="400px" cellspacing="0px" cellpadding="0px" border="1px">
<tr>
<td>图书ID</td>
<td><input type="text" name="id" placeholder="请输入数字" pattern="\d+" required="required"></td>
</tr>
<tr>
<td>图书名</td>
<td><input type="text" name="bookName"></td>
</tr>
<tr>
<td>图书分类</td>
<td>
<select name="catgoryName">
<%
for(String key : maps.keySet()){
%>
<option value="<%=maps.get(key) %>"><%=maps.get(key)%></option>
<%
}
%>
</select>
</td>
</tr>
<tr>
<td>价格</td>
<td><input type="text" name="price" placeholder="请输入价格" ></td>
</tr>
<tr>
<td>描述</td>
<td><input type="text" name="description" placeholder="请输入描述信息"></td>
</tr>
<tr>
<td colspan="2" style="text-align:center">
<input type="submit" value="添加">
<input type="reset" value="重置">
</td>
</tr>
</table>
</form>
</center>
</body>
</html>其他页面没有抒写业务逻辑就不贴出来了
0
收起
正在回答 回答被采纳积分+1
2回答
好帮手慕阿莹
2018-11-01 18:28:36
首先在map中不同的key值不会被覆盖，
不过，同学可以把域想象成一个Map 。同一个key值只能存一个 value，所以，每次往域中key为“map”中存时，会覆盖上次存的map。例如你的代码：
this.getServletContext().setAttribute("map", map);
如果再来一个map，就会把之前的存的覆盖掉了。
所以，
1、我们可以在全局设置一个 List
public static List<Map<String ,String>> mapList = newArraryList<Map<String ,String>>();
2、
然后我们把id，catgoryName，description 等都存到新创建的map中。
Map<String,String> map = new HashMap<String,String>(); map.put(“id”,id ); map.put(“catgoryName”,catgoryName ); map.put(“description ”,description );
3、把这个创建好的map （一个分类） 放到 mapList 中去。
mapList.add(map);
4、最后我们再把这个mapList集合放到域中，可以起名叫 mapList
this.getServletContext().setAttribute("mapList", mapList);这样，每次放一个分类在里边，都可以存在这个mapList，中了。
可以遍历mapList，就可以获取所以添加的类了。
5、建议同学把这个过程放到Dao的实现类中，写成一个方法，在Servlet中，直接调用这个方法，把获取的这几个参数传递给这个方法就可以了。实现了代码的分成，比较清晰。
如果我的回答解决了你的疑惑，请采纳！祝学习愉快！
相似问题
登录后可查看更多问答，登录/注册
从网页搭建入门Java Web2018版
- 参与学习 人
- 提交作业 1088 份
- 解答问题 10205 个
如果你有Java语言基础，又想以后从事Java Web开发，那么本路径是你的不二选择！本路径从网页搭建开始入手，通过大量案例来学习Java Web基础。定能助你完成Java Web小白的蜕变！
了解课程
恭喜解决一个难题，获得1积分~
来为老师/同学的回答评分吧
0 星