实现论坛管理，在mysql中创建论坛表，包含留言时间、留言IP地址、留言内容并且在servlet程序中实现发表留言、留言显示、删除留言

1. 创建论坛表

在MySQL中创建论坛表，包括留言时间、留言IP地址、留言内容等字段。

CREATE TABLE forum (
    id INT(11) NOT NULL AUTO_INCREMENT,
    post_time TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP,
    ip VARCHAR(20) NOT NULL,
    content TEXT NOT NULL,
    PRIMARY KEY (id)
);

2. 实现发表留言

在Servlet中实现发表留言功能，将用户输入的留言内容、留言IP地址等信息插入到论坛表中。

protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    String content = request.getParameter("content");
    String ip = request.getRemoteAddr();
    try {
        Class.forName("com.mysql.jdbc.Driver");
        Connection conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/forum", "root", "password");
        PreparedStatement pstmt = conn.prepareStatement("INSERT INTO forum (ip, content) VALUES (?, ?)");
        pstmt.setString(1, ip);
        pstmt.setString(2, content);
        pstmt.executeUpdate();
        pstmt.close();
        conn.close();
        response.sendRedirect("index.jsp");
    } catch (Exception e) {
        e.printStackTrace();
    }
}

3. 实现留言显示

在Servlet中实现留言显示功能，从论坛表中查询留言记录，并将结果封装成List对象，通过JSP页面展示留言列表。

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    try {
        Class.forName("com.mysql.jdbc.Driver");
        Connection conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/forum", "root", "password");
        Statement stmt = conn.createStatement();
        String sql = "SELECT * FROM forum ORDER BY post_time DESC";
        ResultSet rs = stmt.executeQuery(sql);
        List<ForumPost> posts = new ArrayList<>();
        while (rs.next()) {
            ForumPost post = new ForumPost();
            post.setId(rs.getInt("id"));
            post.setPostTime(rs.getTimestamp("post_time"));
            post.setIp(rs.getString("ip"));
            post.setContent(rs.getString("content"));
            posts.add(post);
        }
        rs.close();
        stmt.close();
        conn.close();
        request.setAttribute("posts", posts);
        request.getRequestDispatcher("index.jsp").forward(request, response);
    } catch (Exception e) {
        e.printStackTrace();
    }
}

4. 实现删除留言

在Servlet中实现删除留言功能，根据留言ID从论坛表中删除对应记录。

protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    int postId = Integer.parseInt(request.getParameter("postId"));
    try {
        Class.forName("com.mysql.jdbc.Driver");
        Connection conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/forum", "root", "password");
        PreparedStatement pstmt = conn.prepareStatement("DELETE FROM forum WHERE id = ?");
        pstmt.setInt(1, postId);
        pstmt.executeUpdate();
        pstmt.close();
        conn.close();
        response.sendRedirect("index.jsp");
    } catch (Exception e) {
        e.printStackTrace();
    }
}