java - request.getParameter 正在检索 'null'

Question

我正在尝试在我的项目中实现 CRUD 功能。我能够在 jsp 上显示数据库表，但是当我尝试删除条目时，出现此错误:(我看到 servlet 中的一行有问题，但不明白为什么它不能检索 bookingID。):

Warning: StandardWrapperValve[UserController]: Servlet.service() for servlet UserController threw exception
java.lang.NumberFormatException: null
	at java.lang.Integer.parseInt(Integer.java:542)
	at java.lang.Integer.parseInt(Integer.java:615)
	at com.daniel.controller.UserController.doGet(UserController.java:34)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:687)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:790)
	at org.apache.catalina.core.StandardWrapper.service(StandardWrapper.java:1682)
	at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:318)
	at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:160)
	at org.apache.catalina.core.StandardPipeline.doInvoke(StandardPipeline.java:734)
	at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:673)
	at com.sun.enterprise.web.WebPipeline.invoke(WebPipeline.java:99)
	at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:174)
	at org.apache.catalina.connector.CoyoteAdapter.doService(CoyoteAdapter.java:416)
	at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:283)
	at com.sun.enterprise.v3.services.impl.ContainerMapper$HttpHandlerCallable.call(ContainerMapper.java:459)
	at com.sun.enterprise.v3.services.impl.ContainerMapper.service(ContainerMapper.java:167)
	at org.glassfish.grizzly.http.server.HttpHandler.runService(HttpHandler.java:206)
	at org.glassfish.grizzly.http.server.HttpHandler.doHandle(HttpHandler.java:180)
	at org.glassfish.grizzly.http.server.HttpServerFilter.handleRead(HttpServerFilter.java:235)
	at org.glassfish.grizzly.filterchain.ExecutorResolver$9.execute(ExecutorResolver.java:119)
	at org.glassfish.grizzly.filterchain.DefaultFilterChain.executeFilter(DefaultFilterChain.java:283)
	at org.glassfish.grizzly.filterchain.DefaultFilterChain.executeChainPart(DefaultFilterChain.java:200)
	at org.glassfish.grizzly.filterchain.DefaultFilterChain.execute(DefaultFilterChain.java:132)
	at org.glassfish.grizzly.filterchain.DefaultFilterChain.process(DefaultFilterChain.java:111)
	at org.glassfish.grizzly.ProcessorExecutor.execute(ProcessorExecutor.java:77)
	at org.glassfish.grizzly.nio.transport.TCPNIOTransport.fireIOEvent(TCPNIOTransport.java:536)
	at org.glassfish.grizzly.strategies.AbstractIOStrategy.fireIOEvent(AbstractIOStrategy.java:112)
	at org.glassfish.grizzly.strategies.WorkerThreadIOStrategy.run0(WorkerThreadIOStrategy.java:117)
	at org.glassfish.grizzly.strategies.WorkerThreadIOStrategy.access$100(WorkerThreadIOStrategy.java:56)
	at org.glassfish.grizzly.strategies.WorkerThreadIOStrategy$WorkerThreadRunnable.run(WorkerThreadIOStrategy.java:137)
	at org.glassfish.grizzly.threadpool.AbstractThreadPool$Worker.doWork(AbstractThreadPool.java:591)
	at org.glassfish.grizzly.threadpool.AbstractThreadPool$Worker.run(AbstractThreadPool.java:571)
	at java.lang.Thread.run(Thread.java:745)

预订.java

package com.daniel.model;

public class Booking {
	
	private int bookingID = -1;
	private String bookingDate = null;
	private String reasoning = null;
	private String bookingStatus = null;
	private String bookingReview = null;
	
	public int getBookingID() {
		return bookingID;
	}
	public void setBookingID(int bookingID) {
		this.bookingID = bookingID;
	}
	public String getBookingDate() {
		return bookingDate;
	}
	public void setBookingDate(String bookingDate) {
		this.bookingDate = bookingDate;
	}
	public String getReasoning() {
		return reasoning;
	}
	public void setReasoning(String reasoning) {
		this.reasoning = reasoning;
	}
	public String getBookingStatus() {
		return bookingStatus;
	}
	public void setBookingStatus(String bookingStatus) {
		this.bookingStatus = bookingStatus;
	}
	public String getBookingReview() {
		return bookingReview;
	}
	public void setBookingReview(String bookingReview) {
		this.bookingReview = bookingReview;
	}
	@Override
	public String toString() {
		  return "Booking [bookingID=" + bookingID + ", bookingDate=" + bookingDate
	                + ", reasoning=" + reasoning + ", bookingStatus=" + bookingStatus + ", bookingReview="
	                + bookingReview + "]";

	}


	
}

BookingDao.java

package com.daniel.dao;

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.ArrayList;
import java.util.List;

import com.daniel.model.Booking;
import com.daniel.util.DbUtil;


public class BookingDao {
	
	private Connection connection;

    public BookingDao() {
        connection = DbUtil.getConnection();
    }

    public void addUser(Booking booking) {
        try {
            PreparedStatement preparedStatement = connection
                    .prepareStatement("insert into booking(booking_id,booking_date,reasoning,booking_status) values (?, ?, ?, 'Upcoming' )");
            // Parameters start with 1
            preparedStatement.setInt(1, booking.getBookingID());
            preparedStatement.setString(2, booking.getBookingDate());
            preparedStatement.setString(3, booking.getReasoning());
            preparedStatement.executeUpdate();

        } catch (SQLException e) {
            e.printStackTrace();
        }
    }

    public void deleteUser(int bookingID) {
        try {
            PreparedStatement preparedStatement = connection
                    .prepareStatement("delete from booking where booking_id=?");
            // Parameters start with 1
            preparedStatement.setInt(1, bookingID);
            preparedStatement.executeUpdate();

        } catch (SQLException e) {
            e.printStackTrace();
        }
    }

    public void updateUser(Booking booking) {
        try {
            PreparedStatement preparedStatement = connection
                    .prepareStatement("update booking set booking_date=?, reasoning=?" +
                            "where booking_id=?");
            // Parameters start with 1
            preparedStatement.setString(1, booking.getBookingDate());
            preparedStatement.setString(2, booking.getReasoning());
            preparedStatement.setInt(3, booking.getBookingID());
            preparedStatement.executeUpdate();

        } catch (SQLException e) {
            e.printStackTrace();
        }
    }

    public List<Booking> getAllUsers() {
        List<Booking> bookings = new ArrayList<Booking>();
        try {
            Statement statement = connection.createStatement();
            ResultSet rs = statement.executeQuery("select * from booking");
            while (rs.next()) {
                Booking booking = new Booking();
                booking.setBookingID(rs.getInt(1));
                booking.setBookingDate(rs.getString(2));
                booking.setReasoning(rs.getString(3));
                booking.setBookingStatus(rs.getString(4));
                booking.setBookingReview(rs.getString(5));
                bookings.add(booking);
                System.out.println(booking);
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }

        return bookings;
    }

    public Booking getUserById(int bookingID) {
        Booking booking = new Booking();
        try {
            PreparedStatement preparedStatement = connection.
                    prepareStatement("select * from booking where booking_id=?");
            preparedStatement.setInt(1, bookingID);
            ResultSet rs = preparedStatement.executeQuery();

            if (rs.next()) {
            	 booking.setBookingID(rs.getInt(1));
                 booking.setBookingDate(rs.getString(2));
                 booking.setReasoning(rs.getString(3));
                 booking.setBookingStatus(rs.getString(4));
                 booking.setBookingReview(rs.getString(5));
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }

        return booking;
    }


}

UserController.java

package com.daniel.controller;


import java.io.IOException;


import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import com.daniel.dao.BookingDao;
import com.daniel.model.Booking;

public class UserController extends HttpServlet {
	
	 private static final long serialVersionUID = 1L;
	    private static String INSERT_OR_EDIT = "/user.jsp";
	    private static String LIST_USER = "/listUser.jsp";
	    private BookingDao dao;

	    public UserController () {
	        super();
	        dao = new BookingDao();
	    }

	    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
	        String forward="";
	        String action = request.getParameter("action");

	        if (action.equalsIgnoreCase("delete")){
	        	System.out.println(request.getParameter("bookingID"));
	            int bookingID = Integer.parseInt(request.getParameter("bookingID"));
	            dao.deleteUser(bookingID);
	            forward = LIST_USER;
	            request.setAttribute("users", dao.getAllUsers());    
	        } else if (action.equalsIgnoreCase("edit")){
	            forward = INSERT_OR_EDIT;
	            int bookingID = Integer.parseInt(request.getParameter("bookingID"));
	            Booking booking = dao.getUserById(bookingID);
	            request.setAttribute("booking", booking);
	        } else if (action.equalsIgnoreCase("listUser")){
	            forward = LIST_USER;
	            request.setAttribute("users", dao.getAllUsers());
	        } else {
	            forward = INSERT_OR_EDIT;
	        }

	        RequestDispatcher view = request.getRequestDispatcher(forward);
	        view.forward(request, response);
	    }

	    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
	        Booking booking = new Booking();
	        booking.setBookingDate(request.getParameter("bookingDate"));
	        booking.setReasoning(request.getParameter("reasoning"));
	        String bookingID = request.getParameter("bookingID");
	        if(bookingID == null || bookingID.isEmpty())
	        {
	            dao.addUser(booking);
	        }
	        else
	        {
	           booking.setBookingID(Integer.parseInt(bookingID));
	            dao.updateUser(booking);
	        }
	        RequestDispatcher view = request.getRequestDispatcher(LIST_USER);
	        request.setAttribute("users", dao.getAllUsers());
	        view.forward(request, response);
	    }


}

listUser.jsp

<%@ page language="java" contentType="text/html; charset=EUC-KR" pageEncoding="EUC-KR"%>
<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c"%>
<%@ taglib uri="http://java.sun.com/jsp/jstl/fmt" prefix="fmt"%>
<!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=EUC-KR">
<title>Show All Users</title>
</head>
<body>
    <table border=1>
        <thead>
            <tr>
                <th>User Id</th>
                <th>First Name</th>
                <th>Last Name</th>
                <th>DOB</th>
                <th>Email</th>
                <th colspan=2>Action</th>
            </tr>
        </thead>
        <tbody>
            <c:forEach items="${users}" var="booking">
                <tr>
                    <td><c:out value="${booking.bookingID}" /></td>
                    <td><c:out value="${booking.bookingDate}" /></td>
                    <td><c:out value="${booking.reasoning}" /></td>
                    <td><c:out value="${booking.bookingStatus}" /></td>
                    <td><c:out value="${booking.bookingReview}" /></td>
                    <td><a href="UserController?action=edit&userId=<c:out value="${booking.bookingID}"/>">Update</a></td>
                    <td><a href="UserController?action=delete&userId=<c:out value="${booking.bookingID}"/>">Delete</a></td>
                </tr>
            </c:forEach>
        </tbody>
    </table>
    <p><a href="UserController?action=insert">Add User</a></p>
</body>
</html>

Answer 1

您要删除的链接使用以下 URL:

UserController?action=delete&userId=<c:out value="${booking.bookingID}"/>

你的代码使用

request.getParameter("bookingID")

很明显，bookingID 参数为空，因为 URL 中没有这样的参数。该参数名为 userId。

请注意，使用链接删除某些内容是一个非常非常糟糕的主意。任何人都可以向您发送包含删除 URL 的链接，如果您单击它:砰!你删除了一个用户。

更糟糕的是:如果该页面被公开，GoogleBot(以及所有其他搜索引擎机器人)将点击页面中的每个链接来抓取您的网站，从而删除所有用户。

使用表单，通过 POST 提交。