Spring配置文件中Bean实例化的三种方式

1.无参构造方法实例化

<bean id="userDao" class="com.itheima.dao.impl.UserDaoImpl" init-method="inti" destroy-method="desto"></bean>

2.工厂静态方法实例化
创建工厂

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

配置告诉spring不要用无参构造

<bean id="factory" class="com.itheima.factory.StaticFactory" factory-method="getUserDao"></bean>

3.工厂实例方法实例化

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

<bean id="factory" class="com.itheima.factory.DynamicFactory"></bean>
<bean id="userDao" factory-bean="factory" factory-method="getUserDao"></bean>