Spring不为人知的功能点-nestedBw
源码如下
【BeanWrapperImpl】
public void setPropertyValue(PropertyValue pv) throws BeansException {
PropertyTokenHolder tokens = (PropertyTokenHolder) pv.resolvedTokens;
if (tokens == null) {
String propertyName = pv.getName();
BeanWrapperImpl nestedBw = null;
try {
nestedBw = getBeanWrapperForPropertyPath(propertyName);
}
catch (NotReadablePropertyException ex) {
throw new NotWritablePropertyException(getRootClass(), this.nestedPath + propertyName,
"Nested property in path '" + propertyName + "' does not exist", ex);
}
tokens = getPropertyNameTokens(getFinalPath(nestedBw, propertyName));
if (nestedBw == this) {
pv.getOriginalPropertyValue().resolvedTokens = tokens;
}
nestedBw.setPropertyValue(tokens, pv);
}
else {
setPropertyValue(tokens, pv);
}
}
这里的nestedBw作何解释，嵌套的Bw功能，自己写了个例子来诠释上面的功能点，如下(大体只需要关注greetingService)：
<?xml version="1.0" encoding="GB2312"?> <beans xmlns="<a href=" xmlns:xsi="<a href=" xmlns:aop="<a href=" xmlns:p="<a href="http://www.springframework.org/schema/p" xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.0.xsd http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop-3.0.xsd" default-autowire="byName"> <bean id="aop" class="org.springframework.aop.framework.autoproxy.DefaultAdvisorAutoProxyCreator" > </bean> <aop:config > </aop:config> <bean id="greetingService" class="GreetingServiceImpl" > <property name="myRef" ref="myRef" /> <property name="myRef.name" value="chenshuai123" /> <property name="greeting" value="Hello karry!" /> <property name="count" value ="12" /> <property name="urls" value ="tmp*.xml" /> </bean> <bean id="count" class="Count"> <property name="greetingService" ref="greetingService" /> </bean> <bean id="myRef" class="MyRef"> <property name="name" value="chenshuai" /> <property name="sex" value="male" /> </bean> <bean id="advice" class="Advice"> </bean> <bean id="adviceAdvisor" class="org.springframework.aop.aspectj.AspectJExpressionPointcutAdvisor"> <property name="advice" ref="advice" /> <property name="expression" value="execution(* *.sayGreeting(..))" /> </bean> </beans>
[GreetingServiceImpl]
public class GreetingServiceImpl implements GreetingService, BeanPostProcessor {
......
public void sayGreeting() {
String n = count;
System.out.println(greeting+n+myRef.getName());
}
场景一：
public class testMain {
public static void main(String[] args) {
//final ApplicationContext factory = new ClassPathXmlApplicationContext("myBeans.xml");
final BeanFactory factory = new XmlBeanFactory(new ClassPathResource("myBeans.xml"));
//BeanPostProcessor aop = (BeanPostProcessor) factory.getBean("aop");
//factory.addBeanPostProcessor(aop);
//MyRef myRef = (MyRef) factory.getBean("myRef");
//System.out.println(myRef.getName());
GreetingService greetingService = (GreetingService) factory.getBean("greetingService");
Resource[] urls = greetingService.getUrls();
greetingService.sayGreeting();
MyRef myRef = (MyRef) factory.getBean("myRef");
System.out.println(myRef.getName());
}
}
输出结果为：
Hello karry!12chenshuai123 chenshuai123
场景二：
public class testMain {
public static void main(String[] args) {
//final ApplicationContext factory = new ClassPathXmlApplicationContext("myBeans.xml");
final BeanFactory factory = new XmlBeanFactory(new ClassPathResource("myBeans.xml"));
//BeanPostProcessor aop = (BeanPostProcessor) factory.getBean("aop");
//factory.addBeanPostProcessor(aop);
MyRef myRef = (MyRef) factory.getBean("myRef");
System.out.println(myRef.getName());
GreetingService greetingService = (GreetingService) factory.getBean("greetingService");
Resource[] urls = greetingService.getUrls();
greetingService.sayGreeting();
//MyRef myRef = (MyRef) factory.getBean("myRef");
//System.out.println(myRef.getName());
}
}
输出结果为：
chenshuai Hello karry!12chenshuai123
场景三：
public class testMain {
public static void main(String[] args) {
final ApplicationContext factory = new ClassPathXmlApplicationContext("myBeans.xml");
//final BeanFactory factory = new XmlBeanFactory(new ClassPathResource("myBeans.xml"));
//BeanPostProcessor aop = (BeanPostProcessor) factory.getBean("aop");
//factory.addBeanPostProcessor(aop);
MyRef myRef = (MyRef) factory.getBean("myRef");
System.out.println(myRef.getName());
GreetingService greetingService = (GreetingService) factory.getBean("greetingService");
Resource[] urls = greetingService.getUrls();
greetingService.sayGreeting();
//MyRef myRef = (MyRef) factory.getBean("myRef");
//System.out.println(myRef.getName());
}
}
输出结果为：
OK OK chenshuai123 before before Hello karry!12chenshuai123
猜猜这次结果为什么是这样呢？
总结
1、只做了一次set，嵌套只对最后一个Bean做set处理
2、不推荐使用嵌套的Bean，因为会因为getBean的次序破坏Bean的唯一性。
3、注意区别嵌套Bean和内部Bean
4、我寻思该功能肯定有特殊的应用场景，暂时不清楚用在哪里比较有优势