使用java+mysql写一个简单的在线投票系统

好的，下面是一个简单的在线投票系统的Java代码，使用MySQL作为数据库：

首先，需要创建一个投票项目的实体类（VoteItem）和投票记录的实体类（VoteRecord）：

public class VoteItem {
    private int id;
    private String name;
    private int count;

    // getter and setter methods
}

public class VoteRecord {
    private int id;
    private int itemId;
    private String voterIp;
    private Date voteTime;

    // getter and setter methods
}

接下来，需要创建一个MySQL数据库，并创建两张表：vote_item用于存储投票项目，vote_record用于存储投票记录。下面是两张表的建表语句：

CREATE TABLE vote_item (
  id INT PRIMARY KEY AUTO_INCREMENT,
  name VARCHAR(100) NOT NULL,
  count INT DEFAULT 0
);

CREATE TABLE vote_record (
  id INT PRIMARY KEY AUTO_INCREMENT,
  item_id INT NOT NULL,
  voter_ip VARCHAR(50) NOT NULL,
  vote_time DATETIME NOT NULL
);

然后，创建一个投票服务类（VoteService），实现投票功能：

public class VoteService {
    private static final String DB_URL = "jdbc:mysql://localhost:3306/vote";
    private static final String DB_USER = "root";
    private static final String DB_PASSWORD = "root";

    private static final String INSERT_VOTE_RECORD_SQL = "INSERT INTO vote_record (item_id, voter_ip, vote_time) VALUES (?, ?, ?)";
    private static final String UPDATE_VOTE_ITEM_SQL = "UPDATE vote_item SET count = count + 1 WHERE id = ?";
    private static final String GET_ALL_VOTE_ITEMS_SQL = "SELECT * FROM vote_item";
    private static final String GET_VOTE_ITEM_SQL = "SELECT * FROM vote_item WHERE id = ?";

    private Connection conn;

    public VoteService() throws SQLException {
        conn = DriverManager.getConnection(DB_URL, DB_USER, DB_PASSWORD);
    }

    public List<VoteItem> getAllVoteItems() throws SQLException {
        List<VoteItem> items = new ArrayList<>();

        try (PreparedStatement ps = conn.prepareStatement(GET_ALL_VOTE_ITEMS_SQL)) {
            ResultSet rs = ps.executeQuery();
            while (rs.next()) {
                VoteItem item = new VoteItem();
                item.setId(rs.getInt("id"));
                item.setName(rs.getString("name"));
                item.setCount(rs.getInt("count"));
                items.add(item);
            }
        }

        return items;
    }

    public VoteItem getVoteItem(int id) throws SQLException {
        try (PreparedStatement ps = conn.prepareStatement(GET_VOTE_ITEM_SQL)) {
            ps.setInt(1, id);
            ResultSet rs = ps.executeQuery();
            if (rs.next()) {
                VoteItem item = new VoteItem();
                item.setId(rs.getInt("id"));
                item.setName(rs.getString("name"));
                item.setCount(rs.getInt("count"));
                return item;
            } else {
                return null;
            }
        }
    }

    public void vote(int itemId, String voterIp) throws SQLException {
        Date voteTime = new Date();

        try (PreparedStatement ps = conn.prepareStatement(INSERT_VOTE_RECORD_SQL)) {
            ps.setInt(1, itemId);
            ps.setString(2, voterIp);
            ps.setTimestamp(3, new Timestamp(voteTime.getTime()));
            ps.executeUpdate();
        }

        try (PreparedStatement ps = conn.prepareStatement(UPDATE_VOTE_ITEM_SQL)) {
            ps.setInt(1, itemId);
            ps.executeUpdate();
        }
    }
}

最后，创建一个投票应用程序（VoteApp），使用Spring Boot框架实现Web界面：

@RestController
public class VoteApp {
    private VoteService voteService;

    @Autowired
    public VoteApp(VoteService voteService) {
        this.voteService = voteService;
    }

    @GetMapping("/vote")
    public ModelAndView vote() throws SQLException {
        List<VoteItem> items = voteService.getAllVoteItems();
        ModelAndView mv = new ModelAndView("vote");
        mv.addObject("items", items);
        return mv;
    }

    @PostMapping("/vote")
    public String doVote(@RequestParam int itemId, HttpServletRequest request) throws SQLException {
        String voterIp = request.getRemoteAddr();
        voteService.vote(itemId, voterIp);
        return "success";
    }

    @GetMapping("/vote/{id}")
    public ModelAndView voteItem(@PathVariable int id) throws SQLException {
        VoteItem item = voteService.getVoteItem(id);
        if (item == null) {
            return new ModelAndView("error");
        } else {
            ModelAndView mv = new ModelAndView("vote_item");
            mv.addObject("item", item);
            return mv;
        }
    }

    public static void main(String[] args) {
        SpringApplication.run(VoteApp.class, args);
    }
}

在resources/templates目录下创建vote.html和vote_item.html两个模板文件，分别用于显示所有投票项目和单个投票项目的投票结果。

最后，启动投票应用程序，访问http://localhost:8080/vote即可进行投票。