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在项目中尝试 在不同的spring的配置文件中分别引入相应的properties文件，这样会在spring配置文件中配置多个PropertyPlaceholderConfigurer实例，但是这样使用的话就会出现key找不到的问题，异常信息如下：
“ Could not resolve placeholder ‘key2”
信息: Destroying singletons in org.springframework.beans.factory.support.DefaultListableBeanFactory@38882d9a: defining beans [propertyConfigurer1,propertyConfigurer2,serviceA,serviceB,resourceServiceImpl]; root of factory hierarchy Exception in thread "main" org.springframework.beans.factory.BeanDefinitionStoreException: Invalid bean definition with name ‘serviceA‘ defined in class path resource [applicationContext.xml]: Could not resolve placeholder ‘key2‘ at org.springframework.beans.factory.config.PropertyPlaceholderConfigurer.processProperties(PropertyPlaceholderConfigurer.java:287) at org.springframework.beans.factory.config.PropertyResourceConfigurer.postProcessBeanFactory(PropertyResourceConfigurer.java:75) at org.springframework.context.support.AbstractApplicationContext.invokeBeanFactoryPostProcessors(AbstractApplicationContext.java:663) at org.springframework.context.support.AbstractApplicationContext.invokeBeanFactoryPostProcessors(AbstractApplicationContext.java:638) at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:407) at org.springframework.context.support.ClassPathXmlApplicationContext.<init>(ClassPathXmlApplicationContext.java:139) at org.springframework.context.support.ClassPathXmlApplicationContext.<init>(ClassPathXmlApplicationContext.java:83) at org.simonme.srcstudy.spring3.demo.service.BeanAssemblyTest.main(BeanAssemblyTest.java:34)
配置形式如下（为了分析问题，配置形式做了简化，但是体现出了原本的意思）：
<bean id="propertyConfigurer1" class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer"> <property name="locations"> <list> <value> classpath:conf/test/test1.properties </value> </list> </property> </bean> <bean id="propertyConfigurer2" class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer"> <property name="locations"> <list> <value> classpath:conf/test/test2.properties </value> </list> </property> </bean> <bean id="serviceA" class="org.simonme.srcstudy.spring3.demo.service.impl.ServiceAImpl"> <property name="field" value="field4AInstacne"/> <property name="key1" value="${key1}"/> <property name="key2" value="${key2}"/> </bean>
Java的service代码如下：
public class ServiceAImpl implements ServiceA { private String field; private String key1; private String key2; /** * 模拟返回测试数据 * @return */ @Override public String queryA() { System.out.println("key1:" + key1); System.out.println("key2:" + key2); return "Query A Result" + field; } public String getField() { return field; } public void setField(String field) { this.field = field; } public String getKey1() { return key1; } public void setKey1(String key1) { this.key1 = key1; } public String getKey2() { return key2; } public void setKey2(String key2) { this.key2 = key2; } }
如果仍然需要使用两个(或多个)PropertyPlaceholderConfigurer实例进行装配，怎样才能解决上面的异常？
<bean id="propertyConfigurer1" class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer"> <property name="ignoreUnresolvablePlaceholders" value="true"/> <property name="locations"> <list> <value> classpath:conf/test/test1.properties </value> </list> </property> </bean>
<property name="ignoreUnresolvablePlaceholders" value="true"/>
加上上面的一行，表示可以忽略未解析到的占位符。这样就不会报错。如果对每个PropertyPlaceholderConfigurer实例都配置了这句话(忽略未解析占位符错误)，那什么时候检查未解析到的占位符呢？
对于未解析到的占位符，可以通过order属性来调整bean装配的优先级，然后在最后装配的PropertyPlaceholderConfigurer实例上面启用未解析到的占位符检查。
分析上述问题涉及的spring代码主要在哪里？
在spring bean装配时，一个PropertyPlaceholderConfigurer就是一个后置处理器BeanFactoryPostProcessor。在装配完PropertyPlaceholderConfigurer之后，就会触发org.springframework.context.support.AbstractApplicationContext.invokeBeanFactoryPostProcessors(Collection<? extends BeanFactoryPostProcessor>, ConfigurableListableBeanFactory)方法，代码如下：
/** * Invoke the given BeanFactoryPostProcessor beans. */ private void invokeBeanFactoryPostProcessors( Collection<? extends BeanFactoryPostProcessor> postProcessors, ConfigurableListableBeanFactory beanFactory) { for (BeanFactoryPostProcessor postProcessor : postProcessors) { postProcessor.postProcessBeanFactory(beanFactory); } }
在每调用完一个BeanFactoryPostProcessor之后，就会去解析所有的bean中引用properties的占位符，这时就会出现占位符不能解析的问题(不能解析的占位在后面的BeanFactoryPostProcessor中，也就是PropertyPlaceholderConfigurer实例)。
spring的多个PropertyPlaceholderConfigurer实例装配的问题
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原文地址：http://www.cnblogs.com/simoncook/p/5652328.html
