数据库连接查询(Statement)，全过程。

public void executeQuery() throws Exception{

        //1.数据库四要素
        InputStream resourceAsStream = this.getClass().getClassLoader().getResourceAsStream("jdbc.properties");

        //2.用Properties，key返回value值
        Properties properties = new Properties();
        properties.load(resourceAsStream);
        String driver = properties.getProperty("jdbc.drivers");
        String url = properties.getProperty("jdbc.url");
        String user = properties.getProperty("jdbc.user");
        String password = properties.getProperty("jdbc.password");

        //3.用Class.forName反射的机制进行对类的对象的生成
        Class.forName(driver);

        //4.用DriverManager连接Driver
        Connection connection = DriverManager.getConnection(url, user, password);
//        System.out.println(connection);

        //5.用connection类下的Statement方法，准备查询
        Statement statement = connection.createStatement();

        //6.用executeQuery查询sql
        String sql = "select * from t_user";
        ResultSet resultSet = statement.executeQuery(sql);

        //6.因为ResultSet里有一个游标为了对数据库进行查询所以使用next()的布尔类型执行while
        //7.将遍历结果放在List里
        List<User> users = new ArrayList<>();
        while(resultSet.next()) {

            int id = resultSet.getInt(1);
            String login_name = resultSet.getString(2);
            String password1 = resultSet.getString(3);
            String user_name = resultSet.getString(4);
            
            //8.创建一个User对象，以便于添加至List
            User user1 = new User(id,login_name,password1,user_name);
            users.add(user1);
            //9.打印结果
            System.out.println(user1);
        }


    }