JAVA JDBC连接步骤代码，SQL注入，处理异常try catch 的快捷键

JAVA JDBC连接步骤代码，SQL注入，处理异常try catch 的快捷键

备注：try catch快捷键：选中代码块，然后Ctrl+Alt+T   //idea

所需文件夹

查询：statement.executeQuery(sql)  返回结果是数据集

package com;

import java.sql.*;

public class Demo1 {
    //备注：try catch快捷键：选中代码块，然后Ctrl+Alt+T
    public static void main(String[] args){
        Connection connection = null;
        Statement statement = null;
        ResultSet resultSet = null;
        try {
            //1.加载驱动
            Class.forName("com.mysql.cj.jdbc.Driver");//mysql8.0以后版本
            //2.获得链接
            String username = "root";
            String passWord = "123456";
            String url = "jdbc:mysql://localhost:3306/mysql2?serverTimezone=UTC";
            connection = DriverManager.getConnection(url, username, passWord);
            //3.定义sql，创建状态通道（进行sql语句的发送）
            statement = connection.createStatement();
            resultSet = statement.executeQuery("select * from emp1");//executeQuery(sql) 执行查询
            //4.取出结果集信息
            while(resultSet.next()){//判断是否有下一条数据
                //取出数据：resultSet.getXXX(“列名”);  xxx表示数据类型
                System.out.println("姓名："+resultSet.getString("ename")+",工资："+resultSet.getDouble("sal")+",雇佣日期:"+resultSet.getDate("hiredate"));
            }
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        } catch (SQLException throwables) {
            throwables.printStackTrace();
        } finally {
            try {
                //5.关闭资源
                if (resultSet != null) {
                    resultSet.close();
                }
                if (statement != null) {
                    statement.close();
                }
                if (connection != null) {
                    connection.close();
                }
            } catch (SQLException throwables) {
                throwables.printStackTrace();
            }
        }
    }
}

增删改：statement.executeUpdate(sql)  返回结果是int类型，指受影响的行数

package com;

import java.sql.*;

public class Demo1 {
    //备注：try catch快捷键：选中代码块，然后Ctrl+Alt+T
    public static void main(String[] args){
        Connection connection = null;
        Statement statement = null;
        try {
            //1.加载驱动
            Class.forName("com.mysql.cj.jdbc.Driver");//mysql8.0以后版本
            //2.获得链接
            String username = "root";
            String passWord = "123456";
            String url = "jdbc:mysql://localhost:3306/mysql2?serverTimezone=UTC";
            connection = DriverManager.getConnection(url, username, passWord);
            //3.定义sql，创建状态通道（进行sql语句的发送）
            statement = connection.createStatement();
            //返回结果为受影响的行数  result的值是受影响的行数
            int result = statement.executeUpdate("insert into emp1(ename,hiredate,sal) values('aa','2020-1-1',2000)");//executeUpdate(sql) 执行增删改时使用
            if(result>0){
                System.out.println("执行成功");
            }else{
                System.out.println("执行失败");
            }
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        } catch (SQLException throwables) {
            throwables.printStackTrace();
        } finally {
            try {
                //5.关闭资源
                if (statement != null) {
                    statement.close();
                }
                if (connection != null) {
                    connection.close();
                }
            } catch (SQLException throwables) {
                throwables.printStackTrace();
            }
        }
    }
}

SQL注入

package com;

import java.sql.*;

public class Demo1 {
    //备注：try catch快捷键：选中代码块，然后Ctrl+Alt+T
    public static void main(String[] args){
        Connection connection = null;
        Statement statement = null;
        ResultSet resultSet = null;
        try {
            //1.加载驱动
            Class.forName("com.mysql.cj.jdbc.Driver");//mysql8.0以后版本
            //2.获得链接
            String username = "root";
            String passWord = "123456";
            String url = "jdbc:mysql://localhost:3306/mysql2?serverTimezone=UTC";
            connection = DriverManager.getConnection(url, username, passWord);
            //3.定义sql，创建状态通道（进行sql语句的发送）
            statement = connection.createStatement();
            String uname = "abcd";
            String pass = " '' or 1=1";
            resultSet = statement.executeQuery("select * from users2 where username='"+uname+"' and password="+pass);//executeQuery(sql) 执行查询
            //4.取出结果集信息
            if(resultSet.next()){
                System.out.println("登陆成功");
            }else{
                System.out.println("登陆失败");
            }
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        } catch (SQLException throwables) {
            throwables.printStackTrace();
        } finally {
            try {
                //5.关闭资源
                if (resultSet != null) {
                    resultSet.close();
                }
                if (statement != null) {
                    statement.close();
                }
                if (connection != null) {
                    connection.close();
                }
            } catch (SQLException throwables) {
                throwables.printStackTrace();
            }
        }
    }
}

防止SQL注入（预状态通道）

package com;

import java.sql.*;

public class Demo1 {
    //备注：try catch快捷键：选中代码块，然后Ctrl+Alt+T
    public static void main(String[] args){
        Connection connection = null;
        PreparedStatement pps = null;
        ResultSet resultSet = null;
        try {
            //1.加载驱动
            Class.forName("com.mysql.cj.jdbc.Driver");//mysql8.0以后版本
            //2.获得链接
            String username = "root";
            String passWord = "123456";
            String url = "jdbc:mysql://localhost:3306/mysql2?serverTimezone=UTC";
            connection = DriverManager.getConnection(url, username, passWord);
            //3.定义sql，创建预状态通道（进行sql语句的发送）
            String sql = "select * from users2 where username=? and password=?";
            pps = connection.prepareStatement(sql);
            String uname = "aa";
            String pass = "1";
            //给占位符赋值 (下标，内容)
            pps.setString(1,uname);
            pps.setString(2,pass);
            //执行sql
            resultSet = pps.executeQuery();
            //4.取出结果集信息
            if(resultSet.next()){
                System.out.println("登陆成功");
            }else{
                System.out.println("登陆失败");
            }
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        } catch (SQLException throwables) {
            throwables.printStackTrace();
        } finally {
            try {
                //5.关闭资源
                if (resultSet != null) {
                    resultSet.close();
                }
                if (pps != null) {
                    pps.close();
                }
                if (connection != null) {
                    connection.close();
                }
            } catch (SQLException throwables) {
                throwables.printStackTrace();
            }
        }
    }
}