JDBCUtils（JDBC工具类）

1.通过.class类文件获取流或者ClassLoader类加载器获取当前src路径下的文件

...\src\pro.properties

url=jdbc:mysql://127.0.0.1:3306/day3?serverTimezone=UTC
user=root
password=root
driver=com.mysql.cj.jdbc.Driver

2.创建类jdbcUtils1包含3个方法

1. 可以把几个字符串定义成边量
   • 用户名
   • 密码
   • URL
   • 驱动类
   • statci{}，静态代码块的内容只随着 类的加载 而加载一次
2. 得到数据库的连接：getConnection()
3. 关闭所有打开的资源
   • close(Connection conn,Statement stmt)
   • close(Connection conn,Statement stmt,ResultSet rs)

package demo.jdbcutils01;

import java.io.FileReader;
import java.io.IOException;
import java.net.URL;
import java.sql.*;
import java.util.Properties;

public class JDBCUtils1 {
    private static String url;
    private static String user;
    private static String password;
    private static String driver;

    public static void main(String[] args) {
        JDBCUtils1 j1 = new JDBCUtils1();
        j1.getConnection();
    }

//执行顺序：（优先级从高到低。）静态代码块>mian方法>构造代码块>构造方法。
// 静态代码块只执行一次。构造代码块在每次创建对象是都会执
//tatic代码块指的是static{}包裹的代码块，可以通过Class.forName("classPath")的方式唤醒代码的static代码块,只执行一次。
//构造块：直接在类中定义且没有加static关键字的代码块称为{}构造代码块。构造代码块在创建对象时被调用，每次创建对象都会被调用

    static {
        Properties p = new Properties();
        ClassLoader classLoader = JDBCUtils1.class.getClassLoader();
        URL resource = classLoader.getResource("jdbc.properties");
        String path = resource.getPath();
//        path = URLDecoder.decode(path,"utf-8");文件路径有中文的话需要转为utf-8编码格式
        try {
            p.load(new FileReader(path));
        } catch (IOException e) {
            e.printStackTrace();
        }
        url = p.getProperty("url");
        user = p.getProperty("user");
        password = p.getProperty("password");
        driver = p.getProperty("driver");
        try {
            Class.forName(driver);
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        }
    }
    public static Connection getConnection(){
        try {
            return DriverManager.getConnection(url,user,password);
        } catch (SQLException e) {
            e.printStackTrace();
            return null;
        }
    }
    public static void close(Connection con, Statement stat){
        if (con != null) {
            try {
                con.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
        if (stat != null) {
            try {
                stat.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }

    }
    public static void close(Connection con, Statement stat, ResultSet set){
        if (con != null) {
            try {
                con.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
        if (stat != null) {
            try {
                stat.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
        if (set != null) {
            try {
                set.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
    }
}

3.jdbcUtil工具类实现，用户登录注册案例

package demo.jdbcutils01;

import netscape.security.UserTarget;

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

public class login_demo {
    private static  Connection con = JDBCUtils1.getConnection();
    private static Statement stat = null;
    private static PreparedStatement pstat = null;
    private static ResultSet set = null;
    private static int i;
    public static void main(String[] args) {
        while (true){
            Scanner scanner = new Scanner(System.in);
            System.out.println("请输入你的选择（1、登录（可SQL注入），2、登录（防止SQL注入）3、注册，4、退出）：");
            String str = scanner.nextLine();
            if (str.equals("4")){
                JDBCUtils1.close(con,stat,set);
                JDBCUtils1.close(con,pstat,set);
                System.exit(0);
            }
            System.out.println("请输入 用户名");
            String username = scanner.nextLine();
            System.out.println("请输入 密码");
            String password = scanner.nextLine();
            switch (str){
                case "1":
                    login(username,password);
                    break;
                case "2":
                    login2(username,password);
                    break;
                case "3":
                    register(username,password);
                    break;
                default:
                    System.out.println("无此选项");
                    break;
            }
        }
    }
    public static void login(String username,String password){
        String sql = "select * from userinfo where username = '"+username+"' and password = '"+password+"';";
        System.out.println(sql);
        try {
            stat = con.createStatement();
            set = stat.executeQuery(sql);
        } catch (SQLException e) {
            e.printStackTrace();
        }
        try {
            if (set.next()){
                System.out.println("登录成功");
            }else {
                System.out.println("登录失败");
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
    public static void login2(String username,String password){
        String sql = "select * from userinfo where username = ? and password = ?;";
        System.out.println(sql);

        try {
            pstat = con.prepareStatement(sql);
            pstat.setString(1,username);
            pstat.setString(2,password);
            set = pstat.executeQuery();
        } catch (SQLException e) {
            e.printStackTrace();
        }
        try {
            if (set.next()){
                System.out.println("登录成功");
            }else {
                System.out.println("登录失败");
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
    public static void register(String username,String password){
        String sql = "insert into userinfo values (null,'"+username+"','"+password+"');";
        System.out.println(sql);
        try {
            stat = con.createStatement();
            i = stat.executeUpdate(sql);
        } catch (SQLException e) {
            e.printStackTrace();
        }
        if (i == 1){
            System.out.println("注册成功");
        }else {
            System.out.println("注册失败");
        }
    }
}