防止sql注入方法 如何防止java中将MySQL的数据库验证密码加上 ' or '1'= '1 就可以出现万能密码 的PreparedStatement

package com.swift;

import java.sql.Connection;

import java.sql.DriverManager;

import java.sql.PreparedStatement;

import java.sql.ResultSet;

import java.sql.SQLException;

public class LoginJDBC$PreparedStatement {

    public static void main(String[] args) {

        User userZhangsan=new User("swift","123456' or '1'='1");

        if(login(userZhangsan)) {

            System.out.println("账号密码正确，登陆成功");

        }else {

            System.out.println("登陆失败");

        }

    }

    private static boolean login(User userZhangsan) {

        Connection conn=null;

        PreparedStatement ps=null;

        ResultSet rs=null;

        try {

            //1、装载驱动

            Class.forName("com.mysql.jdbc.Driver");

        } catch (ClassNotFoundException e) {

            e.printStackTrace();

        }

        try {

            //2、链接数据库，使用com.mysql.jdbc.Connection包会出错

            conn=DriverManager.getConnection("jdbc:mysql://localhost:3306/sw_database?user=root&password=root");

            //3、创建连接语句

            ps=conn.prepareStatement("select * from sw_user where username='"+userZhangsan.getUsername()+"' and password='"+userZhangsan.getPassword()+"'");

            //4、执行ＳＱＬ语句获得结果集

            rs=ps.executeQuery();

            if(rs.next()) {

                return true;

            }

        } catch (SQLException e) {

            e.printStackTrace();

        }finally {

            //关闭结果集

            try {

                if(rs!=null) {

                   rs.close();

                }

            } catch (SQLException e) {

                // TODO Auto-generated catch block

                e.printStackTrace();

            }

            //关闭连接语句

            try {

                if(ps!=null) {

                   ps.close();

                }

            } catch (SQLException e) {

                // TODO Auto-generated catch block

                e.printStackTrace();

            }

            //关闭数据库连接

            try {

                if(conn!=null) {

                    conn.close();

                }

            } catch (SQLException e) {

                // TODO Auto-generated catch block

                e.printStackTrace();

            }

        }

        return false;

    }

}

上面代码中的sql语句通过字符串连接的方式，虽然已经使用了PreparedStatement,但依然不能防止注入，因为字符串连接可以加入'or '1'='1
ps=conn.prepareStatement("select * from sw_user where username='"+userZhangsan.getUsername()+"' and password='"+userZhangsan.getPassword()+"'");
将上面sql语句变为 select * from sw_user where username=? and password=?
就不存在字符串连接，password 加上其他字符sql也无法执行
所以代码修改如下：

package com.swift;

import java.sql.Connection;

import java.sql.DriverManager;

import java.sql.PreparedStatement;

import java.sql.ResultSet;

import java.sql.SQLException;

public class LoginJDBC$PreparedStatement2 {

    public static void main(String[] args) {

        User userSwift=new User("zhangsan","123456");

        if(login(userSwift)) {

            System.out.println("账号密码正确，登陆成功");

        }else {

            System.out.println("登陆失败");

        }

    }

    private static boolean login(User userSwift) {

        Connection conn=null;

        PreparedStatement ps=null;

        ResultSet rs=null;

        try {

            //1、装载驱动

            Class.forName("com.mysql.jdbc.Driver");

        } catch (ClassNotFoundException e) {

            e.printStackTrace();

        }

        try {

            //2、链接数据库，使用com.mysql.jdbc.Connection包会出错

            conn=DriverManager.getConnection("jdbc:mysql://localhost:3306/sw_database?user=root&password=root");

            //3、创建连接语句

            ps=conn.prepareStatement("select * from sw_user where username=? and password=?");

            ps.setString(1, userSwift.getUsername());

            ps.setString(2, userSwift.getPassword());

            //4、执行ＳＱＬ语句获得结果集

            rs=ps.executeQuery();

            if(rs.next()) {

                return true;

            }

        } catch (SQLException e) {

            e.printStackTrace();

        }finally {

            //关闭结果集

            try {

                if(rs!=null) {

                   rs.close();

                }

            } catch (SQLException e) {

                // TODO Auto-generated catch block

                e.printStackTrace();

            }

            //关闭连接语句

            try {

                if(ps!=null) {

                   ps.close();

                }

            } catch (SQLException e) {

                // TODO Auto-generated catch block

                e.printStackTrace();

            }

            //关闭数据库连接

            try {

                if(conn!=null) {

                    conn.close();

                }

            } catch (SQLException e) {

                // TODO Auto-generated catch block

                e.printStackTrace();

            }

        }

        return false;

    }

}