请给出基于Java、mysql、tomcat、html的web候选人投票系统的详细代码

好的，以下是基于Java、MySQL、Tomcat和HTML的Web候选人投票系统的详细代码示例：

1. 数据库设计

创建数据库vote，其中包括两个表格candidate和vote_record。

CREATE DATABASE vote;

USE vote;

CREATE TABLE candidate (
    id INT(11) PRIMARY KEY AUTO_INCREMENT,
    name VARCHAR(50) NOT NULL,
    photo VARCHAR(100),
    description VARCHAR(255)
);

CREATE TABLE vote_record (
    id INT(11) PRIMARY KEY AUTO_INCREMENT,
    user_id INT(11) NOT NULL,
    candidate_id INT(11) NOT NULL,
    vote_time DATETIME DEFAULT CURRENT_TIMESTAMP,
    FOREIGN KEY (user_id) REFERENCES user(id),
    FOREIGN KEY (candidate_id) REFERENCES candidate(id)
);

2. Java Web项目搭建

创建一个新的Java Web项目vote_system，添加如下依赖：

- MySQL JDBC驱动
- Tomcat Servlet API
- JSP API

创建一个名为DBUtil的Java类，用于封装数据库操作。

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;

public class DBUtil {
    private static final String URL = "jdbc:mysql://localhost:3306/vote?useSSL=false&serverTimezone=UTC";
    private static final String USER = "root";
    private static final String PASSWORD = "password";

    public static Connection getConnection() {
        Connection conn = null;
        try {
            Class.forName("com.mysql.jdbc.Driver");
            conn = DriverManager.getConnection(URL, USER, PASSWORD);
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        } catch (SQLException e) {
            e.printStackTrace();
        }
        return conn;
    }

    public static void close(Connection conn, PreparedStatement pstmt, ResultSet rs) {
        try {
            if (rs != null) {
                rs.close();
            }
            if (pstmt != null) {
                pstmt.close();
            }
            if (conn != null) {
                conn.close();
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
}

3. 用户登录

创建一个名为LoginServlet的Servlet，用于处理用户登录请求。

import java.io.IOException;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;

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 javax.servlet.http.HttpSession;

@WebServlet("/login")
public class LoginServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;

    protected void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        String username = request.getParameter("username");
        String password = request.getParameter("password");

        Connection conn = null;
        PreparedStatement pstmt = null;
        ResultSet rs = null;

        try {
            conn = DBUtil.getConnection();
            pstmt = conn.prepareStatement("SELECT id FROM user WHERE username=? AND password=?");
            pstmt.setString(1, username);
            pstmt.setString(2, password);
            rs = pstmt.executeQuery();
            if (rs.next()) {
                HttpSession session = request.getSession();
                session.setAttribute("user_id", rs.getInt("id"));
                response.sendRedirect("candidate_list.jsp");
            } else {
                response.sendRedirect("login.jsp?error=1");
            }
        } catch (SQLException e) {
            e.printStackTrace();
        } finally {
            DBUtil.close(conn, pstmt, rs);
        }
    }
}

4. 候选人列表

创建一个名为CandidateListServlet的Servlet，用于获取候选人列表并在JSP页面中展示。

import java.io.IOException;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.ArrayList;
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;

@WebServlet("/candidate_list")
public class CandidateListServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;

    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        Connection conn = null;
        PreparedStatement pstmt = null;
        ResultSet rs = null;

        try {
            conn = DBUtil.getConnection();
            pstmt = conn.prepareStatement("SELECT id, name, photo, description FROM candidate");
            rs = pstmt.executeQuery();
            List<Candidate> candidates = new ArrayList<Candidate>();
            while (rs.next()) {
                Candidate candidate = new Candidate();
                candidate.setId(rs.getInt("id"));
                candidate.setName(rs.getString("name"));
                candidate.setPhoto(rs.getString("photo"));
                candidate.setDescription(rs.getString("description"));
                candidates.add(candidate);
            }
            request.setAttribute("candidates", candidates);
            request.getRequestDispatcher("candidate_list.jsp").forward(request, response);
        } catch (SQLException e) {
            e.printStackTrace();
        } finally {
            DBUtil.close(conn, pstmt, rs);
        }
    }
}

5. 投票

创建一个名为VoteServlet的Servlet，用于处理用户投票请求。

import java.io.IOException;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Timestamp;

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 javax.servlet.http.HttpSession;

@WebServlet("/vote")
public class VoteServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;

    protected void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        int candidateId = Integer.parseInt(request.getParameter("candidate_id"));

        HttpSession session = request.getSession();
        int userId = (int) session.getAttribute("user_id");

        Connection conn = null;
        PreparedStatement pstmt = null;
        ResultSet rs = null;

        try {
            conn = DBUtil.getConnection();
            pstmt = conn.prepareStatement("SELECT id FROM vote_record WHERE user_id=? AND candidate_id=?");
            pstmt.setInt(1, userId);
            pstmt.setInt(2, candidateId);
            rs = pstmt.executeQuery();
            if (rs.next()) {
                response.sendRedirect("candidate_list.jsp?error=1");
            } else {
                pstmt = conn.prepareStatement("INSERT INTO vote_record (user_id, candidate_id) VALUES (?, ?)");
                pstmt.setInt(1, userId);
                pstmt.setInt(2, candidateId);
                pstmt.executeUpdate();
                response.sendRedirect("candidate_list.jsp");
            }
        } catch (SQLException e) {
            e.printStackTrace();
        } finally {
            DBUtil.close(conn, pstmt, rs);
        }
    }
}

6. JSP页面

最后创建一个名为candidate_list.jsp的JSP页面，用于展示候选人列表并处理用户投票请求。

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core"%>
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>候选人列表</title>
<style type="text/css">
    .candidate {
        margin: 10px;
        padding: 10px;
        border: 1px solid #ddd;
        display: inline-block;
        text-align: center;
        vertical-align: top;
    }

    .candidate img {
        width: 100px;
        height: 100px;
    }
</style>
</head>
<body>
    <h1>候选人列表</h1>
    <c:if test="${not empty param.error}">
        <p style="color: red;">您已经投过票了，请勿重复投票！</p>
    </c:if>
    <c:forEach var="candidate" items="${candidates}">
        <div class="candidate">
            <img src="${candidate.photo}" />
            <p>${candidate.name}</p>
            <p>${candidate.description}</p>
            <form method="post" action="vote">
                <input type="hidden" name="candidate_id" value="${candidate.id}" />
                <button type="submit">投票</button>
            </form>
        </div>
    </c:forEach>
</body>
</html>

以上是基于Java、MySQL、Tomcat和HTML的Web候选人投票系统的详细代码示例。希望能对您有所帮助。