了解ClassLoader：

    /*

     * 了解类的加载器：ClassLoader

     *

     */

@Test

    public void testClassLoader() {

        // 获取到系统类加载器，加载用户自己创建类

        ClassLoader loader = ClassLoader.getSystemClassLoader();

        System.out.println(loader);

        // 获取到扩展类加载器，加载D:\jdk1.6.0_45\jre\lib\ext目录下的jar包

        ClassLoader loader2 = loader.getParent();

        System.out.println(loader2);

        // 引导类加载器，获取不到

        ClassLoader loader3 = loader2.getParent();

        System.out.println(loader3);

    }

    // 举例：对于自定义类，是使用系统类加载器加载

        String className = "com.atguigu.java.Person";

        ClassLoader classLoader = Class.forName(className).getClassLoader();

        System.out.println(classLoader);

        className = "java.lang.String";

        classLoader = Class.forName(className).getClassLoader();

        System.out.println(classLoader);

关于ClassLoader加载器的一个使用，需要掌握

包结构：

================================

jdbc.properties:

jdbc.user=root

jdbc.password=root

jdbc.driverClass=com.mysql.jdbc.Driver

jdbc.jdbcUrl=jdbc:mysql://127.0.0.1:3306/jdbc1

#jdbc.user=scott

#jdbc.password=tiger

#jdbc.driverClass=oracle.jdbc.driver.OracleDriver

#jdbc.jdbcUrl=jdbc:oracle:thin:@127.0.0.1:1521:ORCL001

    /*

     * 关于ClassLoader加载器的一个使用，需要掌握

     */

    @Test

    public void testClassLoader1() throws IOException {

        // 方式一：读取当前工程下的配置文件jdbc.properties

        Properties properties = new Properties();

        FileInputStream inStream = new FileInputStream(new File(

                "jdbc.properties"));

        properties.load(inStream);

        String user = properties.getProperty("jdbc.user");

        String password = properties.getProperty("jdbc.password");

        String driverClass = properties.getProperty("jdbc.driverClass");

        String url = properties.getProperty("jdbc.jdbcUrl");

        System.out.println("user=" + user + "\npassword=" + password

                + "\ndriverClass=" + driverClass + "\nurl" + url);

        System.out.println("============================");

=====================================================

        // 方式二：读取src目录下的配置文件

        Properties properties2 = new Properties();

        // InputStream inputStream =

        // ReflectTest.class.getClassLoader().getResourceAsStream("jdbc1.properties");

        InputStream inputStream = this.getClass().getClassLoader()

                .getResourceAsStream("jdbc1.properties");

        properties2.load(inputStream);

        String user2 = properties2.getProperty("jdbc.user");

        String password2 = properties2.getProperty("jdbc.password");

        String driverClass2 = properties2.getProperty("jdbc.driverClass");

        String url2 = properties2.getProperty("jdbc.jdbcUrl");

        System.out.println("user=" + user2 + "\npassword=" + password2

                + "\ndriverClass=" + driverClass2 + "\nurl" + url2);

        System.out.println("============================");

===============================================

        // 方式三：读包目录下的配置文件

        Properties properties3 = new Properties();

//      InputStream inputStream2 = this.getClass().getClassLoader()

//              .getResourceAsStream("com/atguigu/java/jdbc2.properties");

        InputStream inputStream2 = this.getClass().getClassLoader()

                .getResourceAsStream("com\\atguigu\\java\\jdbc2.properties");

        properties3.load(inputStream2);

        String user3 = properties3.getProperty("jdbc.user");

        String password3 = properties3.getProperty("jdbc.password");

        String driverClass3 = properties3.getProperty("jdbc.driverClass");

        String url3 = properties3.getProperty("jdbc.jdbcUrl");

        System.out.println("user=" + user3 + "\npassword=" + password3

                + "\ndriverClass=" + driverClass3 + "\nurl" + url3);

    }