【Java】JDBC Part1 数据库连接的演变

环境搭建

使用Maven工程的依赖项，如果普通工程就点注释的地址下载jar包即可

<dependencies>
        <!-- https://mvnrepository.com/artifact/mysql/mysql-connector-java -->
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>8.0.19</version>
        </dependency>

        <!-- https://mvnrepository.com/artifact/junit/junit -->
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.13</version>
            <scope>test</scope>
        </dependency>
</dependencies>

原始JDBC链接

    @Test
    public void connectionTest1() throws SQLException {
        // 获取驱动对象
        // 这是8+版本的驱动，5+版本的驱动是这样的com.mysql.jdbc.Driver
        Driver driver = new com.mysql.cj.jdbc.Driver();

        // 注入连接信息 这也是8+的链接方式，必须声明时区，5+版本 jdbc:mysql://localhost:3306/mysql
        String url = "jdbc:mysql://localhost:3306/mysql?serverTimezone=Asia/Shanghai";
        
        // 协议 jdbc:mysql:
        // 地址 localhost:
        // MySQL端口号 3306
        // 数据库 mysql
        // 参数 serverTimezone=Asia/Shanghai"

        // 配置对象封装账户信息
        Properties properties = new Properties();
        properties.setProperty("user","root");
        properties.setProperty("password","123456");

        // 注入信息，得到链接
        Connection connection = driver.connect(url,properties);

        //com.mysql.cj.jdbc.ConnectionImpl@1d548a08
        System.out.println(connection);
    }

演变1 利用反射调取实现类创建驱动实例

    @Test // 提升可移植性，面向接口编程，不要出现第三方的API
    public void connectionTest2() throws SQLException, ClassNotFoundException, IllegalAccessException, InstantiationException {
        //使用反射动态，获取Driver实现类对象
        Class<?> driverClass = Class.forName("com.mysql.cj.jdbc.Driver");
        Driver driver = (Driver) driverClass.newInstance();
        
        String url = "jdbc:mysql://localhost:3306/mysql?serverTimezone=Asia/Shanghai";
        
        Properties properties = new Properties();
        properties.setProperty("user","root");
        properties.setProperty("password","123456");
        
        Connection connection = driver.connect(url,properties);
        
        System.out.println(connection);
    }

演变2 利用驱动管理者实现

    @Test // 用驱动管理者代替驱动对象
    public void connectionTest3() throws SQLException, ClassNotFoundException, IllegalAccessException, InstantiationException {

        Class<?> driverClass = Class.forName("com.mysql.cj.jdbc.Driver");
        Driver driver = (Driver) driverClass.newInstance();

        // 驱动注册
        java.sql.DriverManager.registerDriver(driver);

        String url = "jdbc:mysql://localhost:3306/mysql?serverTimezone=Asia/Shanghai";
        String user = "root";
        String password = "123456";

        // 用驱动管理者配置链接信息去获取连接对象
        Connection connection = DriverManager.getConnection(url, user, password);

        System.out.println(connection);
    }

演变3 驱动优化

    @Test // 驱动再优化
    public void connectionTest4() throws SQLException, ClassNotFoundException, IllegalAccessException, InstantiationException {
        // 注册驱动已经不需要我们来编写了
        Class.forName("com.mysql.cj.jdbc.Driver");
        String url = "jdbc:mysql://localhost:3306/mysql?serverTimezone=Asia/Shanghai";
        String user = "root";
        String password = "123456";
        // 用驱动管理者配置链接信息去获取连接对象
        Connection connection = DriverManager.getConnection(url, user, password);
        System.out.println(connection);
    }

演变4 驱动完全不需要写了 jdbc5+版本支持此写法

    @Test // 驱动再再优化 在5+版本已经不需要驱动这玩意儿了
    public void connectionTest4() throws SQLException, ClassNotFoundException, IllegalAccessException, InstantiationException {
        String url = "jdbc:mysql://localhost:3306/mysql?serverTimezone=Asia/Shanghai";
        String user = "root";
        String password = "123456";
        // 用驱动管理者配置链接信息去获取连接对象
        Connection connection = DriverManager.getConnection(url, user, password);
        System.out.println(connection);
    }

演示5 配置信息不再使用硬编码的方式注入

配置可随意更改，实现了数据和代码的解耦

    @Test //
    public void connectionTest5() throws SQLException, ClassNotFoundException, IOException {
        InputStream inputStream = ConnectorTest.class.getClassLoader().getResourceAsStream("jdbc.properties");

        Properties properties = new Properties();
        properties.load(inputStream);
        
        String driverClass = properties.getProperty("driverClass");
        String url = properties.getProperty("url");
        String user = properties.getProperty("user");
        String password = properties.getProperty("password");

        //加载驱动
        Class.forName(driverClass);
        Connection connection = DriverManager.getConnection(url, user, password);
        System.out.println(connection);
    }

在Maven工程，配置文件放在sources里面

在生成打包文件时，自动生成对应的配置文件

非Maven的普通项目可采用下面这两种方式读取配置文件

    @Test 
    public void connectionTest6() throws SQLException, ClassNotFoundException, IOException {
        // 返回URL的编码 %20  类加载器读取 文件的位置默认是在当前Module或者项目的src包下
        String path = Loader.class.getClassLoader().getResource("jdbc.properties").getFile();
        // 需要解码
        String decode = URLDecoder.decode(path, "UTF-8");
        System.out.println(path);
        System.out.println(decode);
        Properties properties = new Properties();
        properties.load(new FileInputStream(decode));

        String driverClass = properties.getProperty("driverClass");
        String url = properties.getProperty("url");
        String user = properties.getProperty("user");
        String password = properties.getProperty("password");

        //加载驱动
        Class.forName(driverClass);
        Connection connection = DriverManager.getConnection(url, user, password);
        System.out.println(connection);
    }

    @Test //
    public void connectionTest7() throws SQLException, ClassNotFoundException, IOException {
       
        Properties properties = new Properties();
        properties.load(new FileInputStream("src\\jdbc.properties"));

        String driverClass = properties.getProperty("driverClass");
        String url = properties.getProperty("url");
        String user = properties.getProperty("user");
        String password = properties.getProperty("password");

        //加载驱动
        Class.forName(driverClass);
        Connection connection = DriverManager.getConnection(url, user, password);
        System.out.println(connection);
    }