jdbc各个对象详解(2)

最新推荐文章于 2021-03-28 14:09:06 发布

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#jdbc各个对象详解(2)

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本文通过三种登录方法的对比，介绍了如何使用PreparedStatement来防止SQL注入，确保应用程序的安全性。详细展示了PreparedStatement的使用方法，并解释了其相较于传统Statement的优势。

PreparedStatement:

执行sql的对象. 该使用安全!

例子:

package com.ujn.jdbcDemo.jdbc_basic;

import com.ujn.jdbcUtils.DBUtils;

import java.sql.*;
import java.util.Scanner;

public class Login {

    public static void main(String[] args) {
        if (Login.login_method2()){
            System.out.println("登录成功!");
        }else {
            System.out.println("登陆失败!");
        }
    }

    /**
     * 登录方法1---(安全)
     */
    public static boolean login_method1(){
        Scanner sc = new Scanner(System.in);
        System.out.println("请输入用户名:");
        String name = sc.next();
        System.out.println("请输入密码:");
        String pass = sc.next();
        if (name == null || pass == null){
            return false;
        }
        Connection conn = null;
        Statement stat = null;
        ResultSet res = null;
        try {
            conn = DBUtils.getConn();
            String sql = "select * from logininfos";
            stat = conn.createStatement();
            res = stat.executeQuery(sql);
            while (res.next()){
                if (name.equals(res.getString("username")) && pass.equals(res.getString("password"))){
                    return true;
                }
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            DBUtils.close(res, stat, conn);
        }
        return false;
    }

    /**
     * 登录方法2---(不安全 存在sql注入)
     */
    public static boolean login_method2(){
        Scanner sc = new Scanner(System.in);
        System.out.println("请输入用户名:");
        String name = sc.next();
        System.out.println("请输入密码:");
        String pass = sc.next();
        if (name == null || pass == null){
            return false;
        }
        Connection conn = null;
        Statement stat = null;
        ResultSet res = null;
        try {
            conn = DBUtils.getConn();
            String sql = "select * from logininfos where username ='" + name + "'and password ='" + pass +"'";
            System.out.println(sql);
            stat = conn.createStatement();
            res = stat.executeQuery(sql);
            return res.next();
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            DBUtils.close(res, stat, conn);
        }
        return false;
    }

    /**
     * 登录方法3---(安全 使用了PreparedStatement)
     */
    public static boolean login_method3(){
        Scanner sc = new Scanner(System.in);
        System.out.println("请输入用户名:");
        String name = sc.next();
        System.out.println("请输入密码:");
        String pass = sc.next();
        if (name == null || pass == null){
            return false;
        }
        Connection conn = null;
        PreparedStatement pstat = null;
        ResultSet res = null;
        try {
            conn = DBUtils.getConn();
            String sql = "select * from logininfos where username = ? and password = ?";
            pstat = conn.prepareStatement(sql);
            pstat.setString(1, name);
            pstat.setString(2, pass);
            res = pstat.executeQuery();
            return res.next();
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            DBUtils.close(res, pstat, conn);
        }
        return false;
    }

}