1、bean的作用？

        定义Spring核心容器管理的对象。

2、如何使用？

    <beans>
        <bean/>
        <bean></bean>
    </beans>

示例：

    <bean id="bookDao" class="com.spring.dao.impl.BookDaoImpl"/>
    <bean id="bookService" class="com.spring.service.impl.BookServiceImpl">
        <property name="bookDao" ref="bookDao"/>
    </bean>

---

bean实例化

1、构造方法实例化（常用）

提供方法

public class BookDaoImpl implements BookDao {

    public BookDaoImpl(){
        System.out.println("111");
    }

    public void save(){
        System.out.println("book dao save ...");
    }
}

配置（类似中间容器，绑定关系）

    <bean 
            id="bookDao" 
            class="com.spring.dao.impl.BookDaoImpl"/>

使用（先获取容器中的bean，再使用其方法）

public class APP2 {
    public static void main(String[] args) {
        //3.获取IoC容器
        ApplicationContext ctx = new ClassPathXmlApplicationContext("applicationContext.xml");
        //4.获取bean
        BookDao bookDao = (BookDao) ctx.getBean("bookDao");
        bookDao.save();
    }
}

 

 

2、静态工厂实例化

静态工厂

public class OrderDaoFactory {
    public static OrderDao getOrderDao(){
        return new OrderDaoImpl();
    }
}

配置

    <bean 
            id="orderDao" 
            class="com.spring.factory.OrderDaoFactory" 
            factory-method="getOrderDao"/>

3、实例工厂实例化

实例工厂

public class UserDaoFactory {
    public UserDao getUserDao(){
        return new UserDaoImpl();
    }
}

配置

    <bean id="userFactory" class="com.spring.factory.UserDaoFactory"/>
    <bean id="userDao" factory-method="getUserDao" factory-bean="userFactory"/>

 

4、FactoryBean实例化（实用）

FactoryBean

public class UserDaoFactoryBean implements FactoryBean<UserDao> {
    @Override
    //代替原始实例工厂中创建对象的方法
    public UserDao getObject() throws Exception {
        return new UserDaoImpl();
    }

    @Override
    public Class<?> getObjectType() {
        return UserDao.class;
    }
}

UserDaoImpl类

public class UserDaoImpl implements UserDao {
    public void save(){
        System.out.println("user dao save");
    }
}

配置

    <bean id="userDao" class="com.spring.factory.UserDaoFactoryBean"/>

使用

public class AppForInstanceUser {
    public static void main(String[] args) {

        ApplicationContext ctx = new ClassPathXmlApplicationContext("applicationContext.xml");
        UserDao userDao = (UserDao) ctx.getBean("userDao");
        userDao.save();
    }
}