使用过滤器完成添加留言模块 insert.jsp：包含表单及非法文字提示 InsertMessage.java：接受表单参数，jdbc操作数据库 要求： 进行中文字符处理 如果提交内容中有非法字符串，将该字符串保存在request对象发送回insert.jsp，并显示““xxx”是非法文字”。（设定多个非法字符串） 如果登录非法，转发回insert.jsp。

下面是一个使用过滤器完成添加留言模块的示例代码：

InsertMessage.java：

import java.io.IOException;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.SQLException;
import java.text.SimpleDateFormat;
import java.util.Date;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class InsertMessage extends HttpServlet {
    private static final long serialVersionUID = 1L;

    protected void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        request.setCharacterEncoding("UTF-8");
        String name = request.getParameter("name");
        String content = request.getParameter("content");
        String ip = request.getRemoteAddr();
        Date date = new Date();
        SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
        String time = sdf.format(date);

        Connection conn = null;
        PreparedStatement stmt = null;
        try {
            Class.forName("com.mysql.jdbc.Driver");
            String url = "jdbc:mysql://localhost:3306/test?useSSL=false&characterEncoding=UTF-8";
            String user = "root";
            String password = "123456";
            conn = DriverManager.getConnection(url, user, password);
            String sql = "INSERT INTO messages(name, content, time, ip) VALUES (?, ?, ?, ?)";
            stmt = conn.prepareStatement(sql);
            stmt.setString(1, name);
            stmt.setString(2, content);
            stmt.setString(3, time);
            stmt.setString(4, ip);
            stmt.executeUpdate();
            response.sendRedirect("list.jsp");
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        } catch (SQLException e) {
            e.printStackTrace();
        } finally {
            if (stmt != null) {
                try {
                    stmt.close();
                } catch (SQLException e) {
                    e.printStackTrace();
                }
            }
            if (conn != null) {
                try {
                    conn.close();
                } catch (SQLException e) {
                    e.printStackTrace();
                }
            }
        }
    }
}

InsertFilter.java：

import java.io.IOException;
import java.util.Arrays;
import java.util.List;
import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletRequest;

public class InsertFilter implements Filter {
    private List<String> illegalWords;

    public void init(FilterConfig config) throws ServletException {
        String illegalWordsStr = config.getInitParameter("illegalWords");
        illegalWords = Arrays.asList(illegalWordsStr.split(","));
    }

    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
            throws IOException, ServletException {
        HttpServletRequest req = (HttpServletRequest) request;
        String name = req.getParameter("name");
        String content = req.getParameter("content");

        for (String word : illegalWords) {
            if (name.contains(word) || content.contains(word)) {
                request.setAttribute("illegalWord", word);
                req.getRequestDispatcher("insert.jsp").forward(request, response);
                return;
            }
        }

        chain.doFilter(request, response);
    }

    public void destroy() {
        illegalWords = null;
    }
}

在web.xml文件中配置过滤器：

<filter>
    <filter-name>InsertFilter</filter-name>
    <filter-class>InsertFilter</filter-class>
    <init-param>
        <param-name>illegalWords</param-name>
        <param-value>非法1,非法2,非法3</param-value>
    </init-param>
</filter>
<filter-mapping>
    <filter-name>InsertFilter</filter-name>
    <url-pattern>/insert.jsp</url-pattern>
</filter-mapping>

在insert.jsp中添加表单和提示信息：

<%@ page language="java" contentType="text/html; charset=UTF-8" pageEncoding="UTF-8"%>
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>添加留言</title>
</head>
<body>
    <h1>添加留言</h1>
    <form action="InsertMessage" method="post">
        姓名：<input type="text" name="name"><br>
        内容：<textarea name="content"></textarea><br>
        <input type="submit" value="提交">
    </form>
    <%
        String illegalWord = (String) request.getAttribute("illegalWord");
        if (illegalWord != null) {
            out.println("<p>" + illegalWord + "是非法文字</p>");
        }
    %>
</body>
</html>

在上面的代码中，`InsertFilter`过滤器用于过滤表单提交的内容，如果提交内容中包含非法字符串，则将该字符串保存在request对象中，并转发回insert.jsp页面，同时显示提示信息。如果提交内容合法，则继续执行后续操作。