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

在mysql中创建论坛表的SQL语句：

CREATE TABLE forum (
    id INT AUTO_INCREMENT PRIMARY KEY,
    post_time TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
    ip_address VARCHAR(15) NOT NULL,
    content TEXT NOT NULL
);

在servlet程序中实现发表留言、留言显示、删除留言的代码示例：

import java.io.IOException;
import java.sql.*;
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("/ForumServlet")
public class ForumServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;
    private static final String DB_URL = "jdbc:mysql://localhost:3306/forumdb?useSSL=false&serverTimezone=UTC";
    private static final String DB_USER = "root";
    private static final String DB_PASS = "password";

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        String action = request.getParameter("action");
        if (action == null) {
            action = "list";
        }
        switch (action) {
            case "new":
                showNewForm(request, response);
                break;
            case "insert":
                insertPost(request, response);
                break;
            case "delete":
                deletePost(request, response);
                break;
            case "list":
            default:
                listPosts(request, response);
                break;
        }
    }

    private void listPosts(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        List<Post> postList = new ArrayList<>();
        try (Connection conn = DriverManager.getConnection(DB_URL, DB_USER, DB_PASS);
             PreparedStatement stmt = conn.prepareStatement("SELECT * FROM forum ORDER BY post_time DESC");
             ResultSet rs = stmt.executeQuery()) {
            while (rs.next()) {
                Post post = new Post();
                post.setId(rs.getInt("id"));
                post.setPostTime(rs.getTimestamp("post_time"));
                post.setIpAddress(rs.getString("ip_address"));
                post.setContent(rs.getString("content"));
                postList.add(post);
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }
        request.setAttribute("postList", postList);
        request.getRequestDispatcher("forum.jsp").forward(request, response);
    }

    private void showNewForm(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        request.getRequestDispatcher("new_post.jsp").forward(request, response);
    }

    private void insertPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        String ipAddress = request.getRemoteAddr();
        String content = request.getParameter("content");
        try (Connection conn = DriverManager.getConnection(DB_URL, DB_USER, DB_PASS);
             PreparedStatement stmt = conn.prepareStatement("INSERT INTO forum (ip_address, content) VALUES (?, ?)")) {
            stmt.setString(1, ipAddress);
            stmt.setString(2, content);
            stmt.executeUpdate();
        } catch (SQLException e) {
            e.printStackTrace();
        }
        response.sendRedirect("ForumServlet?action=list");
    }

    private void deletePost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        int id = Integer.parseInt(request.getParameter("id"));
        try (Connection conn = DriverManager.getConnection(DB_URL, DB_USER, DB_PASS);
             PreparedStatement stmt = conn.prepareStatement("DELETE FROM forum WHERE id = ?")) {
            stmt.setInt(1, id);
            stmt.executeUpdate();
        } catch (SQLException e) {
            e.printStackTrace();
        }
        response.sendRedirect("ForumServlet?action=list");
    }
}

在jsp页面中显示论坛留言的代码示例：

<%@ 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>Forum</title>
</head>
<body>
    <h1>Forum</h1>
    <a href="ForumServlet?action=new">New Post</a>
    <br><br>
    <table border="1">
        <tr>
            <th>ID</th>
            <th>Date/Time</th>
            <th>IP Address</th>
            <th>Content</th>
            <th>Action</th>
        </tr>
        <c:forEach items="${postList}" var="post">
            <tr>
                <td>${post.id}</td>
                <td>${post.postTime}</td>
                <td>${post.ipAddress}</td>
                <td>${post.content}</td>
                <td><a href="ForumServlet?action=delete&id=${post.id}">Delete</a></td>
            </tr>
        </c:forEach>
    </table>
</body>
</html>

在jsp页面中发表新留言的代码示例：

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>New Post</title>
</head>
<body>
    <h1>New Post</h1>
    <form action="ForumServlet?action=insert" method="post">
        <textarea name="content" rows="10" cols="50"></textarea>
        <br>
        <input type="submit" value="Post">
    </form>
</body>
</html>