Spring中实例化Bean的三种方式

<?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-2.5.xsd">

<!--第一种方式：直接实例化Bean-->

<bean id="personservice1" class="com.binyong.service.PersonServiceBean"></bean>

<!--第二种方式：通过静态工厂方法实例化Bean-->

<!--注意：用这种方式实例化Bean时，工厂方法必须是static的-->

<bean id="personservice2" class="com.binyong.service.impl.PersonServiceBeanFactory" factory-method="createPersonServiceBean"></bean>

<!--第三种方式：通过调用工厂实例的工厂方法实例化Bean，该方法可以不是static的-->

<!--注意：这种方式实例化Bean时，必须先实例化工厂Bean-->

<bean id="PersonServiceBeanFactory" class="com.binyong.service.impl.PersonServiceBeanFactory"></bean>

<bean id="personservice3" factory-bean="PersonServiceBeanFactory" factory-method="createPersonServiceBean2" depends-on="PersonServiceBeanFactory"></bean>

</beans>

获取Bean的代码：

ApplicationContext ctx = new ClassPathXmlApplicationContext(new String[]{"beans.xml"});

PersonServiceBean psb = (PersonServiceBean)ctx.getBean("personservice1");

第一种方式可能出现的异常：

1. org.springframework.beans.factory.CannotLoadBeanClassException: Cannot find class [com.binyong.service.PersonServiceBean] for bean with name 'personservice1' defined in class path resource [beans.xml]; nested exception is java.lang.ClassNotFoundException: com.binyong.service.PersonServiceBean

可能导致异常的原因：class属性中类配置出现问题

第二种方式可能导致的异常

1.org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'personservice2' defined in class path resource [beans.xml]: No matching factory method found: factory method 'createPersonServiceBean'

可能导致异常的原因：工厂方法没有定义为静态方法。

第三种方式可能导致的异常

1.org.springframework.beans.factory.NoSuchBeanDefinitionException: No bean named 'PersonServiceBeanFactory' is defined

可能导致异常的原因：没有先实例化工厂Bean，必须先配置工厂Bean。

在定义bean是可以指定depends-on属性设置先实例化的bean,如本例子中的

depends-on="PersonServiceBeanFactory". 否则就要在应用中明确初始化该bean

2.org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'personservice3' defined in class path resource [beans.xml]: No matching factory method found: factory bean 'PersonServiceBeanFactory'; factory method 'createPersonServiceBean2'

可能导致异常的原因：factory-method对应的工厂方法定义成了静态的。