关于spring属性占位符用法

<bean
	class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer">
	<property name="location">
		<value>classpath:spring/beans/placeholder/attr.properties</value>
	</property>
	<property name="placeholderPrefix" value="${"></property>
	<property name="placeholderSuffix" value="}"></property>
</bean>
<bean id="placeHolderBean" class="spring.beans.placeholder.PlaceHolderBean">
	<property name="id" value="${placeholder.id}"></property>
	<property name="name" value="${placeholder.name}"></property>
	<property name="refBean" ref="${placeholder.ref}"></property>
</bean>
<bean id="refedBean" class="spring.beans.placeholder.RefedBean"></bean>

placeholder.id = 123
placeholder.name = cyy
placeholder.ref = refedBean

<context:property-placeholder
	location="classpath:spring/beans/placeholder/attr.properties" />
<bean id="placeHolderBean" class="spring.beans.placeholder.PlaceHolderBean">
	<property name="id" value="${placeholder.id}"></property>
	<property name="name" value="${placeholder.name}"></property>
	<property name="refBean" ref="${placeholder.ref}"></property>
</bean>
<bean id="refedBean" class="spring.beans.placeholder.RefedBean"></bean>

protected void doProcessProperties(ConfigurableListableBeanFactory beanFactoryToProcess,
		StringValueResolver valueResolver) {
 
	BeanDefinitionVisitor visitor = new BeanDefinitionVisitor(valueResolver);
 
	String[] beanNames = beanFactoryToProcess.getBeanDefinitionNames();
	for (String curName : beanNames) {
		// Check that we're not parsing our own bean definition,
		// to avoid failing on unresolvable placeholders in properties file locations.
		if (!(curName.equals(this.beanName) && beanFactoryToProcess.equals(this.beanFactory))) {
			BeanDefinition bd = beanFactoryToProcess.getBeanDefinition(curName);
			try {
				visitor.visitBeanDefinition(bd);
			}
			catch (Exception ex) {
				throw new BeanDefinitionStoreException(bd.getResourceDescription(), curName, ex.getMessage(), ex);
			}
		}
	}
 
	// New in Spring 2.5: resolve placeholders in alias target names and aliases as well.
	beanFactoryToProcess.resolveAliases(valueResolver);
 
	// New in Spring 3.0: resolve placeholders in embedded values such as annotation attributes.
	beanFactoryToProcess.addEmbeddedValueResolver(valueResolver);
}