本文研究Spring分层Bean Factory用法，先看有关代码：
1 parent.xml
2
3 <!DOCTYPE beans PUBLIC "-//SPRING//DTD BEAN//EN"
"http://www.springframework.org/dtd/spring-beans.dtd">
4 <beans>
5 <bean id="injectBean" class="java.lang.String">
6 <constructor-arg>
7 <value>Bean In Parent</value>
8 </constructor-arg>
9 </bean>
10 <bean id="injectBeanParent" class="java.lang.String">
11 <constructor-arg>
12 <value>Bean In Parent</value>
13 </constructor-arg>
14 </bean>
15 </beans>
1 beans.xml
2
3 <!DOCTYPE beans PUBLIC "-//SPRING//DTD BEAN//EN"
"http://www.springframework.org/dtd/spring-beans.dtd">
4 <beans>
5 <!-- hierarchical bean factories -->
6 <bean id="target1" class="SimpleTarget">
7 <property name="val">
8 <ref bean="injectBeanParent"/>
9 </property>
10 </bean>
11
12 <bean id="target2" class="SimpleTarget">
13 <property name="val">
14 <ref local="injectBean"/>
15 </property>
16 </bean>
17
18 <bean id="target3" class="SimpleTarget">
19 <property name="val">
20 <ref parent="injectBean"/>
21 </property>
22 </bean>
23
24 <bean id="injectBean" class="java.lang.String">
25 <constructor-arg>
26 <value>Bean In Child</value>
27 </constructor-arg>
28 </bean>
29 </beans>
30
SimpleTarget中只有一属性String val
1 public static void main(String[] args) {
2 BeanFactory parent = new XmlBeanFactory(new FileSystemResource(
3 "build/parent.xml"));
4 BeanFactory child = new XmlBeanFactory(new FileSystemResource(
5 "build/beans.xml"), parent);
6
7 SimpleTarget target1 = (SimpleTarget) child.getBean("target1");
8 SimpleTarget target2 = (SimpleTarget) child.getBean("target2");
9 SimpleTarget target3 = (SimpleTarget) child.getBean("target3");
10
11 System.out.println(target1.getVal());
12 System.out.println(target2.getVal());
13 System.out.println(target3.getVal());
14 }
运行结果：
Bean In Parent
Bean In Child
Bean In Parent
分析过程：
在bean factory被加载过程中分别加载各层Bean Factory，
BeanFactory parent
= new XmlBeanFactory(new FileSystemResource("build/parent.xml"));
BeanFactory child = new XmlBeanFactory(new FileSystemResource("build/beans.xml"
), parent);
其中parent参数指定了bean factory间的父子关系。
分析结果：
第一行结果为在父factory中定义的参数，说明在子fantory中可以直接调用父fantory元素，类似于java中的继承关系。
第二行结果说明
<
ref
local
="injectBean"
/>中local指向本fantory元素。
第三行结果为Bean In Parent，说明
<
ref
parent
="injectBean"
/>中parent指向父fantory中元素。
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