实例化bean的四种方法

方法一：用构造方法实例化bean

提供可靠的构造方法，不写默认调用无参构造方法

//配置
<bean id="bookDao" class="org.wcx.dao.impl.BookDaoImpl"/>

 

方法二：用静态工厂实例化bean

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

//配置
<bean id="orderDao" class="org.wcx.dao.factory.OrderDaoFactory" factory-method="getOrderDao"/>

 

方法三：用实例工厂实例化bean

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

}

//配置
<bean id="userDaoFactory" class="org.wcx.dao.factory.UserDaoFactory" />
<bean id="userDao" factory-bean="userDaoFactory" factory-method="getUserOrder"/>

 

方法四：FactoryBean

public class UserDaoFactoryBean implements FactoryBean<UserDao> {

    @Override
    public UserDao getObject() throws Exception {
        return new UserDaoImpl();
    }

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

//配置
<bean id="userDao" class="org.wcx.dao.factory.UserDaoFactoryBean"/>