获取连接

public class JdbcTest {

    /**
     * 1、完整流程
     */
    @Test
    public void test1() throws SQLException {
        // 1.定义要素
        String driverName = "com.mysql.cj.jdbc.Driver";
        String url = "jdbc:mysql://localhost:3306/student?useUnicode=true&characterEncoding=utf8&&useSSL=false&serverTimezone=GMT%2B8";
        String username = "root";
        String password = "root";

        // 2.加载驱动,实例化驱动
        Driver driver = new Driver();

        // 3.注册驱动
        DriverManager.registerDriver(driver);

        // 4.获取连接
        Connection connection = DriverManager.getConnection(url, username, password);

        System.out.println(connection);
    }

    /**
     * 2、反射加载驱动
     */
    @Test
    public void test2() throws SQLException, ClassNotFoundException {
        // 1.定义要素
        String driverName = "com.mysql.cj.jdbc.Driver";
        String url = "jdbc:mysql://localhost:3306/student?useUnicode=true&characterEncoding=utf8&&useSSL=false&serverTimezone=GMT%2B8";
        String username = "root";
        String password = "root";

        // 2.加载驱动,实例化驱动。并注册驱动
        // 仅仅需要jvm加载一下
        Class.forName(driverName);

        // 4.获取连接
        Connection connection = DriverManager.getConnection(url, username, password);

        System.out.println(connection);
    }

    /**
     * 3、jvm主动加载驱动：SPI机制
     */
    @Test
    public void test3() throws SQLException {
        // 1.定义要素
        String url = "jdbc:mysql://localhost:3306/student?useUnicode=true&characterEncoding=utf8&&useSSL=false&serverTimezone=GMT%2B8";
        String username = "root";
        String password = "root";

        // 4.获取连接
        Connection connection = DriverManager.getConnection(url, username, password);

        System.out.println(connection);
    }

}

结果：

com.mysql.cj.jdbc.ConnectionImpl@37d31475

Process finished with exit code 0

我们并没有加载驱动，但是获取到了MySQL的驱动实现。这是JDK主动加载的，涉及到SPI机制。