servlet返回空白页面和数据库未更新。

首先，需要确保servlet代码正确、没有报错和异常，可以通过日志或在控制台打印信息进行调试。其次，需要检查数据库连接是否成功，以及是否正确执行了SQL语句。以下是一个基本的servlet代码，用于插入数据到MySQL数据库：

import java.io.IOException;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
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;

@WebServlet("/AddDataServlet")
public class AddDataServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;
       
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        String name = request.getParameter("name");
        String email = request.getParameter("email");
        
        Connection conn = null;
        PreparedStatement pstmt = null;
        
        try {
            // 1. 加载MySQL JDBC驱动
            Class.forName("com.mysql.jdbc.Driver");
            
            // 2. 获取数据库连接
            conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/test", "root", "password");
            
            // 3. 创建PreparedStatement对象，设置SQL语句
            String sql = "INSERT INTO users (name, email) VALUES (?, ?)";
            pstmt = conn.prepareStatement(sql);
            pstmt.setString(1, name);
            pstmt.setString(2, email);
            
            // 4. 执行SQL语句
            int rows = pstmt.executeUpdate();
            
            // 5. 检查是否插入成功，根据结果返回相应信息
            if (rows > 0) {
                response.getWriter().println("Data added successfully!");
            } else {
                response.getWriter().println("Failed to add data!");
            }
        } catch (ClassNotFoundException | SQLException e) {
            e.printStackTrace();
        } finally {
            // 6. 关闭数据库连接和PreparedStatement对象
            try {
                if (pstmt != null) {
                    pstmt.close();
                }
                if (conn != null) {
                    conn.close();
                }
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }