修改功能时emp取值为null，无法修改，请帮忙看看，谢谢

javabean：Emp类

package com.imooc.bean;
public class Emp {
    private String account;
    private String name;
    private String password;
    private String email;

    //无参构造方法
    public Emp() {
    }

    //带参构造方法
    public Emp(String account, String name, String password, String email) {
        this.setAccount(account);
        this.setName(name);
        this.setPassword(password);
        this.setEmail(email);
    }

    //get&set方法
    public String getAccount() {
        return account;
    }

    public void setAccount(String account) {
        this.account = account;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password;
    }

    public String getEmail() {
        return email;
    }

    public void setEmail(String email) {
        this.email = email;
    }
}

DBUtil类：

package com.imooc.db;

import com.imooc.bean.Emp;

import java.util.HashMap;
import java.util.Map;

public class DBUtil {
    public static Map<String, Emp> map = new HashMap<String, Emp>();

    static {
        map.put("1001", new Emp("1001", "AA", "123456", "AA@email.com"));
        map.put("1002", new Emp("1002", "BB", "123456", "BB@email.com"));
        map.put("1003", new Emp("1003", "CC", "123456", "CC@email.com"));
        map.put("1004", new Emp("1004", "DD", "123456", "DD@email.com"));
    }

    /**
     * 判断用户名和密码是否正确
     */
    public static boolean selectEmpByAccountAndPassword(Emp emp) {
        boolean flag = false;
        for (String key : map.keySet()) {
            Emp e = map.get(key);
            if (emp.getAccount().equals(e.getAccount()) && emp.getPassword().equals(e.getPassword())) {
                flag = true;
                break;
            }
        }
        return flag;
    }
}

Jsp页面-update.jsp

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>员工信息更新</title>
    <style>

        td{
            text-align: center;
            background: #d0eaff;;
        }
        h3{
            color: blue;
        }

    </style>
</head>
<body>
    <h3 align="right">登录账号:<%=session.getAttribute("account")%></h3>
    <h2 align="center">员工信息更新</h2>
    <hr>
    <form action="update_control.jsp">
        <table align="center" width="600px">
            <tr>
                <td>账号:</td>
                <td><input type="text" name="account"  value="<%=request.getParameter("account")%>" readonly></td>
            </tr>
            <tr>
                <td>名称:</td>
                <td><input type="text" name="name"  value="<%=request.getParameter("name")%>"></td>
            </tr>
            <tr>
                <td>邮箱:</td>
                <td><input type="text" name="email"  value="<%=request.getParameter("email")%>"></td>
            </tr>
            <tr>
                <td colspan="2"><input type="submit" value="修改"></td>
            </tr>
        </table>
    </form>
</body>
</html>

Jsp页面-control.jsp

<%@ page contentType="text/html;charset=UTF-8" language="java"  import="com.imooc.db.*,com.imooc.bean.*" errorPage="error.jsp" %>
<%@ page import="java.util.Map" %>
<html>
<head>
    <title>Title</title>
    <style>

        td{
            text-align: center;
            background: #d0eaff;;
        }
        h3{
            color: blue;
        }

    </style>
</head>
<body>
    <%
        String account = request.getParameter("account");
        String password = request.getParameter("password");
        Emp emp = new Emp(account,null,password,null);
        boolean flag = DBUtil.selectEmpByAccountAndPassword(emp);
        Map<String,Emp> map =DBUtil.map;

        if (flag==true){
            session.setAttribute("account",account);
            session.setMaxInactiveInterval(10);
            Object o = application.getAttribute("count");
            if (o==null){
                application.setAttribute("count",1);
            }else{
                int count = Integer.parseInt(o.toString());
                application.setAttribute("count",count+1);
            }
            session.setAttribute("account",account);
    %>
    <h3 align="right">该页面访问量为:<%= application.getAttribute("count")%></h3>
    <h3 align="right" >登录账号:<%= session.getAttribute("account")%></h3>
    <h2 align="center">欢迎来到人事管理系统首页</h2>
    <hr>
    <table align="center" border="1" width="600px">
        <tr>
            <td>账号</td>
            <td>员工姓名</td>
            <td>员工邮箱</td>
            <td>修改</td>
        </tr>

            <%
                for (String key: map.keySet()) {
                    Emp e = map.get(key);
            %>
                <tr>
                    <td><%= e.getAccount() %></td>
                    <td><%= e.getName() %></td>
                    <td><%= e.getEmail() %></td>
                    <td>
                        <a href="update.jsp?account= <%= e.getAccount()%>&name=<%= e.getName() %>&email=<%= e.getEmail() %>">修改</a>
                    </td>
                </tr>
            <%
            }
            %>
    </table>
    <%
    }else{
            throw new Exception("账号或密码错误,登录失败,请重新输入!");
        }
    %>
</body>
</html>

Jsp页面-update_control.jsp

<%@ page language="java" contentType="text/html; charset=UTF-8" errorPage="error.jsp"
         pageEncoding="UTF-8" import="com.imooc.db.*,com.imooc.bean.*,java.util.*"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
    <meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
    <title>Insert title here</title>
</head>
<body>
<%
    Map<String,Emp> map = DBUtil.map;
    Emp emp = map.get(request.getParameter("account"));
    emp.setName(request.getParameter("name"));
    emp.setEmail(request.getParameter("email"));
%>
<h3 align="center">员工信息修改成功</h3>
</body>
</html>

jarive 2018-05-17

源自：JSP内置对象 4-7 信息修改功能

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3回答

一叶知秋519 2018-05-17 14:02:02

emp没有获取到值，所以后面再对emp进行操作时会出现空指针异常；

建议同学通过这种方式来完成：

String account=request.getParameter("account")；

如果account不为空再进行emp的赋值操作；

祝学习愉快！

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提问者 jarive #1

谢谢你的回答不过这种试了不行的后来知道什么原因了可能是拿到的account的值有空格的原因吧，清除空格就好了修改代码如下： Emp emp = map.get(request.getParameter("account").trim());

2018-05-17 15:10:00