我在 servlet 准备语句 [duplicate] 中收到空指针异常

问：

java.lang.NullPointerException：无法调用“java.sql.PreparedStatement.setString（int， String）”，因为“this.statement”为空

注册.java

package in.adit.controller;

import java.io.IOException;
import java.io.PrintWriter;
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("/Registration")
public class Registration extends HttpServlet {
    private static final long serialVersionUID = 1L;

    private static final String URL = "jdbc:mysql://localhost:3306/user";
    private static final String USERNAME = "root";
    private static final String PASSWORD = "";

    Connection connection = null;
    PreparedStatement statement = null;

    public Registration() {
        super();
        try {
            Class.forName("com.mysql.cj.jdbc.Driver");
            connection = DriverManager.getConnection(URL, USERNAME, PASSWORD);
            System.out.println("Connect established succesfully");
        } catch (SQLException e) {
            e.printStackTrace();
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        }
    }

    protected void service(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        // TODO Auto-generated method stub
        String un = request.getParameter("username");
        String pass = request.getParameter("password");
        String firstName = request.getParameter("password");
        String lastName = request.getParameter("password");
        String email = request.getParameter("password");
        String m = request.getParameter("mobile");
        System.out.println(m);
        Long mobile = Long.parseLong(m);

        response.setContentType("text/html");
        PrintWriter out = response.getWriter();     
        try {
            String query2 = "INSERT INTO login_tbl VALUES (?,?)";
            //statement = connection.prepareStatement(query2);
            statement.setString(1,un);
            statement.setString(2,pass);
            statement.execute(query2);
            System.out.println("Query 2 Executed...");
            
            String query = "INSERT INTO user_info_tbl VALUES (?,?,?,?,?)";
            //statement = connection.prepareStatement(query);
            statement.setString(1, un);
            statement.setString(2, firstName);
            statement.setString(3, lastName);
            statement.setString(4, email);
            statement.setLong(5, mobile);
            statement.execute(query);
            System.out.println("Query 1 Executed...");
            
            response.sendRedirect("login.jsp");
        } catch (SQLException e) {
            out.println(e);
            e.printStackTrace();
        }

    }

}

Sigup.html

<%@include file="components/header.jsp" %>
<%@include file="components/navbar.jsp" %>
<div class="row">
    <div class="col-md-4"></div>
    <div class="col-md-4">
        <div class="card">
            <div class="card-header bg-danger">Create Account</div>
            <div class="card-body">

                <form action="Registration" method="get">
                <table class="table table-borderless">
                    <tr>
                        <td><input type="text" class="form-control" name="username"
                            placeholder="Enter Username" /></td>
                    </tr>
                    <tr>
                        <td><input type="password" class="form-control"
                            name="password" placeholder="Enter Password" /></td>
                    </tr>
                    <tr>
                        <td><input type="text" class="form-control" name="firstname"
                            placeholder="Enter Firstname" /></td>
                    </tr>
                    <tr>
                        <td><input type="text" class="form-control" name="lastname"
                            placeholder="Enter Lastname" /></td>
                    </tr>
                    <tr>
                        <td><input type="email" class="form-control" name="email"
                            placeholder="Enter Email" /></td>
                    </tr>
                    <tr>
                        <td><input type="tel" class="form-control" name="mobile"
                            placeholder="Mobile Number 10 digit" pattern="[0-9]{10}" /></td>
                    </tr>
                    <tr>
                        <td><input type="submit" class="btn btn-danger"
                            value="Create Account" /></td>
                    </tr>
                </table>
                </form>
            </div>
        </div>
    </div>
    <div class="col-md-4"></div>
</div>
<%@include file="components/footer.jsp" %>0

我尝试将查询直接放入 xamp 中的 mySql 数据库，这是我的代码，它有效，因此查询是正确的，并且在 jsp 中获取方法显示所有参数传入 url