为什么这个异常Java？

本文介绍了为什么这个异常Java？的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！

问题描述

我正在研究servlet，我正在尝试创建一个小程序，以便通过我创建的类获取小时数。但是我有一个例外。以下是代码：

用户

  
 
 public class User {
 
 private String userId; 
 
 public User（）{
 userId =; 
} 
 
 public User（String id）{
 userId = id; 
} 
 
 public void setUserId（String id）{
 userId = id; 
} 
 
 public String getUserId（）{
 return userId; 
} 
 
}

小时

  package业务; 
 
 import java.util.Calendar; 
 import java.util.GregorianCalendar; 
 
 import business.User; 
 
 public class Hours {
 
 private User user; 
 private Calendar cal = new GregorianCalendar（）; 
 private int min = 0; 
 
 public Hours（用户用户）{
 this.user = user; 
 min = cal.get（Calendar.MINUTE）; 
} 
 
 public String getMinutes（）{
 return Integer.toString（min）; 
} 
 
 public User getUser（）{
 return user; 
} 
 
}

CheckUser

 包过程; 
 
 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; 
 
 import Business.User; 
 import Business.Hours; 
 
 public class CheckUser extends HttpServlet {
 
 protected void processRequest（HttpServletRequest request，HttpServletResponse response）
 throws ServletException，IOException {
 String userId = request。的getParameter（ 用户ID）; 
用户user1 =新用户（userId）; 
小时h1 =新小时（user1）; 
 String url =/show.jsp; 
 
 request.setAttribute（hours，h1）; 
 
 RequestDispatcher dispatcher = getServletContext（）。getRequestDispatcher（url）; 
 dispatcher.forward（request，response）; 
 
} 
 
 @Override 
 protected void doGet（HttpServletRequest request，HttpServletResponse response）
 throws ServletException，IOException {
 String userId = request .getParameter（ 用户ID）; 
用户user1 =新用户（userId）; 
小时h1 =新小时（user1）; 
 String url =/show.jsp; 
 
 request.setAttribute（hours，h1）; 
 
 RequestDispatcher dispatcher = getServletContext（）。getRequestDispatcher（url）; 
 dispatcher.forward（request，response）; 
} 
 
 
 @Override 
 protected void doPost（HttpServletRequest request，HttpServletResponse response）
 throws ServletException，IOException {
 String userId = request .getParameter（ 用户ID）; 
用户user1 =新用户（userId）; 
小时h1 =新小时（user1）; 
 String url =/show.jsp; 
 
 request.setAttribute（hours，h1）; 
 
 RequestDispatcher dispatcher = getServletContext（）。getRequestDispatcher（url）; 
 dispatcher.forward（request，response）; 
} 
 
}

索引

 <％@ page contentType =text / htmlpageEncoding =UTF-8％> 
<！DOCTYPE html> 
< html> 
< head> 
< meta http-equiv =Content-Typecontent =text / html; charset = UTF-8> 
< title> Project< / title> 
< / head> 
< body> 
< h1>员工< / h1> 
< form action =<％= response.encodeURL（CheckUser）％>方法= GET > 
< input type =submitvalue =Diogo> 
< input type =hiddenname =userIdvalue =1> 
< / form> 
< / body> 
< / html>

显示

 <！DOCTYPE html> 
< html> 
< head> 
< meta http-equiv =Content-Typecontent =text / html; charset = UTF-8> 
< title> JSP页面< / title> 
< / head> 
< body> 
<％@ page import =Business。*，process。*％> 
 
<％
小时h1 =（小时）request.getAttribute（小时）; 
 String userId = h1.getUser（）。getUserId（）; 
％> 
< h1><％= userId％>< / h1> 
< / body> 
< / html>

异常

解决方案

你的包是 package Business; 小时你使用的类 import business.User;
记得包是区分大小写的标准它应该是小写的

I'm studying servlets and I'm trying to create a small program to get the hour through a class that I've created. But I've bee getting a exception. Here is the code:

User

package Business;

public class User {

    private String userId;

    public User() {
        userId = "";
    }

    public User(String id) {
        userId = id;
    }

    public void setUserId(String id) {
        userId = id;
    }

    public String getUserId() {
        return userId;
    }

}

Hours

package Business;

import java.util.Calendar;
import java.util.GregorianCalendar;

import business.User;

public class Hours {

    private User user;
    private Calendar cal = new GregorianCalendar();
    private int min = 0;

    public Hours(User user) {
        this.user = user;
        min = cal.get(Calendar.MINUTE);
    }

    public String getMinutes() {
        return Integer.toString(min);
    }

    public User getUser() {
        return user;
    }

}

CheckUser

package process;

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;

import Business.User;
import Business.Hours;

public class CheckUser extends HttpServlet {

    protected void processRequest(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        String userId = request.getParameter("userID");
        User user1 = new User(userId);
        Hours h1 = new Hours(user1);
        String url = "/show.jsp";

        request.setAttribute("hours", h1);

        RequestDispatcher dispatcher = getServletContext().getRequestDispatcher(url);
        dispatcher.forward(request, response);

    }

    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        String userId = request.getParameter("userID");
        User user1 = new User(userId);
        Hours h1 = new Hours(user1);
        String url = "/show.jsp";

        request.setAttribute("hours", h1);

        RequestDispatcher dispatcher = getServletContext().getRequestDispatcher(url);
        dispatcher.forward(request, response);
    }


    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        String userId = request.getParameter("userID");
        User user1 = new User(userId);
        Hours h1 = new Hours(user1);
        String url = "/show.jsp";

        request.setAttribute("hours", h1);

        RequestDispatcher dispatcher = getServletContext().getRequestDispatcher(url);
        dispatcher.forward(request, response);
    }

}

Index

<%@page contentType="text/html" pageEncoding="UTF-8"%>
<!DOCTYPE html>
<html>
    <head>
        <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
        <title>Project</title>
    </head>
    <body>
        <h1>Employees</h1>
        <form action="<%=response.encodeURL("CheckUser")%>" method="get">
            <input type="submit" value="Diogo">
            <input type="hidden" name="userId" value="1">
        </form>
    </body>
</html>

Show

<!DOCTYPE html>
<html>
    <head>
        <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
        <title>JSP Page</title>
    </head>
    <body>
        <%@ page import="Business.*, process.*" %>

        <%
            Hours h1 = (Hours) request.getAttribute("hours");
            String userId =h1.getUser().getUserId();
        %>
        <h1><%= userId %></h1>
    </body>
</html>

Exception

解决方案

your package is package Business; but Hours class you have used import business.User;remember package is case sensitive and as per standard it should be in lowercase

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