Spring初探(IOC,AOP,DI)

class UserDaoImpl implements UserDao {
    //数据库连接信息，需要一些配置，但是又不能写在这个类中(硬编码，改的时候麻烦)
    private String jdbcUrl = "...";
    private String driverClass;
    private String username;
    private String password;
    // ...
}

jdbc.properties
----------------
jdbcUrl = ....
driverClass = ....
...
...

class UserServiceImpl{
        //和具体的实现类耦合在一起了
        //private UserDao userDao = new UserDaoImpl();
        //可以采用工厂的方式解决这个问题
    private UserDao userDao = Factory.getUserDao();

}
工厂里可以采用反射生成实例    

jdbcUrl        = jdbc:mysql:///test2
driverClass    = com.mysql.jdbc.Driver
username       = root
password       = root

public class UserDaoImpl implements UserDao {
    private String jdbcUrl;
    private String driverClass;
    private String username;
    private String password;
    // ...
    public UserDaoImpl() {
        // 读取配置文件
        String resource = "cn/itcast/spring/a_helloworld/jdbc.properties";//一定要加包名
        Properties props = loadProperties(resource);
        // 并初始化信息
        jdbcUrl = props.getProperty("jdbcUrl");
        driverClass = props.getProperty("driverClass");
        username = props.getProperty("username");
        password = props.getProperty("password");
    }

    /**
     * 加载配置文件  
     */
    private Properties loadProperties(String resource) {
        InputStream inputStream = null;
        try {
            //带类加载器(getClassLoader())的情况资源要加包名,因为这种情况是在classpath下面查找。
            //cn/itcast/spring/a_helloworld/jdbc.properties
            inputStream = this.getClass().getClassLoader().getResourceAsStream(resource);
            Properties props = new Properties();
            props.load(inputStream);
            return props;
        } catch (IOException e) {
            throw new RuntimeException(e);
        } finally {
            try {
                inputStream.close();
            } catch (IOException e) {
                throw new RuntimeException(e);
            }
        }
    }
}

// 一、定义工厂类
public class BeanFactory {
    // 用于存放“对象名--实现类的全名”这种对应关系的键值对集合
    private static Properties properties;

    static {
        // 读取配置文件 ObjectFactory.properties，具体代码略。
        properties.load(inStream);
    }

    // 可创建对象实例的工厂方法，接受的参数是对象名，如UserDao、RoleDao等

public static <T>T getBeanInstance(Class<T> clazz) {
        try {
            String className = props.getProperty(clazz.getSimpleName());
            return (T)Class.forName(className).newInstance();
        } catch (Exception e) {
            throw new RuntimeException(e);
        }
    }

}

// 二、使用工厂生成实例
# UserDao = cn.itcast.dao.impl.MySQLUserDaoImpl
# UserDao = cn.itcast.dao.impl.OracleUserDaoImpl
UserDao = cn.itcast.dao.impl.MySQLUserDaoImpl

// 三、使用工厂生成实例
public class UserServiceImpl {
    private UserDao userDao = (UserDao) BeanFactory.getBeanInstance("UserDao");
    // ...
}

当我们把依赖对象交给外部容器负责创建，那么PersonServiceBean 类可以改成如下：
public class PersonServiceBean {
     private PersonDao personDao ; // 要有getter与setter

     // 通过构造器参数，让容器把创建好的依赖对象注入进PersonServiceBean
     public PersonServiceBean(PersonDao personDao){
         this.personDao=personDao;
     }
    // 当然也可以使用setter方法进行注入。
　　public void save(Person person){ personDao.save(person); } }

　　<!-- 配置UserDao对象，需要注入一些配置 -->
    <bean id="userDao" class="cn.itcast.spring.b_springhelloworld.UserDaoImpl">
         //name是UserDaoImpl中的属性名
        <property name="jdbcUrl" value="jdbc:mysql:///test111"></property>
        <property name="driverClass" value="com.mysql.jdbc.Driver"></property>
        <property name="username" value="root"></property>
        <property name="password" value="root"></property>
    </bean>
    <!-- 配置UserService对象，需要依赖UserDao对象 -->
    <bean id="userService" class="cn.itcast.spring.b_springhelloworld.UserServiceImpl">
        <property name="userDao" ref="userDao"></property>
    </bean>

@Test
public void testGetUserDao() {
    // Spring的容器对象
    ApplicationContext applicationContext = new ClassPathXmlApplicationContext("cn/itcast/spring/b_springhelloworld/applicationContext.xml");
　　

   // Spring的容器对象
   Resource resource = new ClassPathResource("cn/itcast/spring/b_springhelloworld/applicationContext.xml");
   BeanFactory beanFactory = new XmlBeanFactory(resource);

// 从中取出配置的Bean
   UserDao userDao = (UserDao) applicationContext.getBean("userDao");
   UserService userService = (UserServiceImpl) applicationContext.getBean("userService");
}