PrepareedStatement 可以防止SQL注入

package com.kuang.lesson03;
import com.kuang.lesson02.utils.JdbcUtils;
import java.util.Date;
import java.sql.*;
public class TestInsert {
    public static void main(String[] args) throws SQLException {
        Connection conn = null;
        PreparedStatement st =null;
        try {
            conn= JdbcUtils.getConnection();
            //区别
            //使用？占位符代替参数
            String sql="insert into users(id,`NAME`,`PASSWORD`,`email`,`birthday`) values(?,?,?,?,?)";
            st=conn.prepareStatement(sql);//预编译，先写sql，然后不执行
            st.setInt(1,4);//id
            st.setString(2,"qiangjiang");//name
            st.setString(3,"123123");
            st.setString(4,"2233445");
            //注意点： sql.Date  数据库   java.sql.Date()
            //       util.Date   Java     new Date().getTime  获得时间戳
            st.setDate(5,new java.sql.Date(new Date().getTime()));
            //执行
            int i = st.executeUpdate();
            if(i>0){
                System.out.println("插入成功");
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }finally {
            JdbcUtils.release(conn,st,null);
        }
    }
}

其他的类似，只需要改sql语句和手动给参即可。
删除类似：

更新：

查询：

package com.kuang.lesson03;
import com.kuang.lesson02.utils.JdbcUtils;
import javax.annotation.Resource;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
public class TestSelect {
    public static void main(String[] args) throws SQLException {
        Connection conn=null;
        PreparedStatement st=null;
        ResultSet rs=null;
        try {
            conn=JdbcUtils.getConnection();
            String sql="select * from users where id = ?";
            st=conn.prepareStatement(sql);
            st.setInt(1,1);
            rs=st.executeQuery();
            if(rs.next()){
                System.out.println(rs.getString("NAME"));
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }finally {
            JdbcUtils.release(conn,st,rs);
        }
    }
}

如何解决sql注入问题？

package com.kuang.lesson03;

import com.kuang.lesson02.utils.JdbcUtils;

import java.sql.*;

public class SqlInjection {
    public static void main(String[] args) {
//    login("zhansan","123456");
    login("''or '1=1","123456");
}
    public static void login(String username,String password){
        Connection conn=null;
        PreparedStatement st=null;
        ResultSet rs=null;

        try {
            conn= JdbcUtils.getConnection();


            //SELECT * FROM users WHERE `name` = 'zhansan' AND `password` = '123456';
            String sql="SELECT * FROM users WHERE `NAME` = ? and `PASSWORD`=?";
            st=conn.prepareStatement(sql);

            st.setString(1,username);
            st.setString(2,password);
            rs=st.executeQuery();
            while (rs.next()){
                System.out.println(rs.getString("NAME"));
                System.out.println(rs.getString("password"));
                System.out.println("=====================================");
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }finally {
            try {
                JdbcUtils.release(conn,st,rs);
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
    }
}

Preparedstatement 防止SQL注入的本质，把传递进来的参数当做字符
假设其中存在转义字符，比如说 ` 会被直按转义