将数据库字符串值与 getParameter html 值进行比较？答案

【问题标题】：Compare a database String value to an getParameter html value?将数据库字符串值与 getParameter html 值进行比较？
【发布时间】：2016-11-03 13:59:24
【问题描述】：

我有一个本地数据库、一个登录页面和一个 servlet。我可以从数据库中获取我想要的值，例如用户名和密码。我还可以在 html 登录表单中获取用户输入。我对 html 使用 request.getParameter。我想检查数据库中的用户名是否等于输入的用户名，如果数据库中的密码等于输入的密码，则授予访问权限，否则拒绝访问。这是我的代码：

 /*
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 * To change this template file, choose Tools | Templates
 * and open the template in the editor.
 */
package com.Servlet;

import static com.sun.corba.se.spi.presentation.rmi.StubAdapter.request;
import java.sql.*;
import java.io.IOException;
import java.io.PrintWriter;
import java.io.StringWriter;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.Scanner;
import javax.servlet.RequestDispatcher;
import javax.sql.DataSource;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 *
 * @author Jony
 */
public class LoginServlet extends HttpServlet {

    private static Object request;

    public static void main(String[] args) throws SQLException, ClassNotFoundException {
        Connection connection = null;
        Statement stmt = null;



        try {
            //STEP 2: Register JDBC driver
            Class.forName("com.mysql.jdbc.Driver");
        } catch (Exception e) {
        }
        //STEP 3: Open a connection
        System.out.println("Connecting to database...");
        connection = DriverManager
                .getConnection("jdbc:mysql://localhost:3306/user_pass", "user", "pass");

        //STEP 4: Execute a query
        System.out.println("Creating statement...");
        stmt = connection.createStatement();
        String sql;
        sql = "SELECT username, password FROM information";
        ResultSet rs = stmt.executeQuery(sql);

        while (rs.next()) {
            //retrieve by column name
            String usernamedb = rs.getString("username");
            String passworddb = rs.getString("password");

            if (usernamedb.equals(inputUsername) && passworddb.equals(inputPassword)) {
                System.out.println("Login successful " + usernamedb + " " + passworddb);
            } else {
                System.out.println("Login failed " + usernamedb + " " + passworddb);
            }

        }

    }

    /**
     *
     * @param request
     * @param response
     * @throws ServletException
     * @throws IOException
     */
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

      PrintWriter out = response.getWriter();
      String title = "Welcome";
      String docType =
      "<!doctype html public \"-//w3c//dtd html 4.0 " +
      "transitional//en\">\n";
      out.println(docType + title);

      String inputUsername = request.getParameter("Name");
      String inputPassword = request.getParameter("Pass");
    }
}

【问题讨论】：

标签： java html database servlets

【解决方案1】：

我认为您只是在学习 servlet。我还看到您是 HvA 的学生，我也是，我们正在学习同一学科。继续上课，问问你的老师，这一切都会变得清晰。目前，此代码将按照您想要的方式运行：

package servlet;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintWriter;
import java.sql.*;

/**
 * @author Jony
 */
public class LoginServlet extends HttpServlet {

    private static Object request;

    private boolean isValidUser(String username, String password) {
        Connection connection = null;
        Statement stmt = null;
        ResultSet rs = null;

        try {
            //STEP 2: Register JDBC driver
            Class.forName("com.mysql.jdbc.Driver");

            //STEP 3: Open a connection
            System.out.println("Connecting to database...");
            connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/user_pass", "user", "pass");

            //STEP 4: Execute a query
            System.out.println("Creating statement...");
            stmt = connection.createStatement();
            String sql = "SELECT username, password FROM information WHERE username='" + username + "' AND password = '" + password + "';";
            rs = stmt.executeQuery(sql);

            // Return true if a result is found.
            if (rs != null && rs.next()) {
                return true;
            }
        } catch (SQLException | ClassNotFoundException e) {
            e.printStackTrace();
        }
        // Return false if no result is found or if there was an error.
        return false;
    }

    /**
     * @param request
     * @param response
     * @throws ServletException
     * @throws IOException
     */
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

        PrintWriter out = response.getWriter();
        String title = "Welcome";
        String docType =
                "<!doctype html public \"-//w3c//dtd html 4.0 " +
                        "transitional//en\">\n";
        out.println(docType + title);

        String inputUsername = request.getParameter("username");
        String inputPassword = request.getParameter("password");

        // Check if user is valid.
        boolean validUser = isValidUser(inputUsername, inputPassword);

        // If user is valid, go to ...
        if (validUser) {
            System.out.println("Login successful");
        }// If user is not valid, do ...
        else {
            System.out.println("Login failed.");
        }

    }
}

有些事情可以改进，比如使用prepared statements，但这也将在以后的课程中教授。编码愉快！

【讨论】：

【解决方案2】：

您正在混合基于命令行的 java 应用程序和 servlet 基础应用程序。请参考https://www.tutorialspoint.com/servlets/servlets-database-access.htm 了解基本的 servlet 数据库示例。

【讨论】：

【解决方案3】：

你会改变你的主要方法为打击

public static void main(String[] args) throws SQLException, ClassNotFoundException {

    Connection connection = null;

        try {
            //STEP 2: Register JDBC driver
            Class.forName("com.mysql.jdbc.Driver");
        } catch (Exception e) {
        }
        //STEP 3: Open a connection
        System.out.println("Connecting to database...");
        connection = DriverManager
                .getConnection("jdbc:mysql://localhost:3306/user_pass", "user", "pass");

        //STEP 4: Execute a query
        System.out.println("Creating statement...");
        sql = "SELECT username, password FROM information";
        PreparedStatement ps = connection.prepareStatement(sql);

        ResultSet rs = ps.executeQuery();

        while (rs.next()) {
            //retrieve by column name
            String usernamedb = rs.getString("username");
            String passworddb = rs.getString("password");

            if (usernamedb.equals(inputUsername) && passworddb.equals(inputPassword)) {
                System.out.println("Login successful " + usernamedb + " " + passworddb);
            } else {
                System.out.println("Login failed " + usernamedb + " " + passworddb);
            }

        }
}

【讨论】：