Spring配置文件-Bean实例化的三种方式

1.无参构造方法实例化（详见我的博客）
2.工厂静态方法实例化
创建StaticFactory类

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

UserDaoImpl类

public class UserDaoImpl implements UserDao {

    public UserDaoImpl(){
        System.out.println("UserDaoImpl被创建了");
    }
    
    @Override
    public void save() {
        System.out.println("save running...");
    }
}

配置applicationContext.xml文件
告诉spring使用什么实例化

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd">
<!--    <bean id="userDao" class="com.hao.dao.impl.UserDaoImpl" ></bean>-->

    <bean id="userDao" class="com.hao.factory.StaticFactory" factory-method="getUserDao"></bean>
</beans>

其中的class是静态类的全限定类名，factory-method是静态类中的方法名，因为该类是静态的，所以不需要创建该类对象，直接调用即可
然后测试

public class SpringTest {

    @Test
    //测试scope属性
    public void test1(){
        ApplicationContext app=new ClassPathXmlApplicationContext("applicationContext.xml");
        UserDao userDao1 = (UserDao) app.getBean("userDao");
        System.out.println(userDao1);
    }
}

3.工厂实例方法实例化
创建工厂类DynamicFactory

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

application的配置

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd">

<!--    让spring先创建factory工厂对象-->
    <bean id="factory" class="com.hao.factory.DynamicFactory"></bean>
<!--    配置userDao的唯一标识id，factory-bean表示我要找这个factory工厂，然后找到找到getUserDao方法-->
    <bean id="userDao" factory-bean="factory" factory-method="getUserDao"></bean>
</beans>