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spring的多个PropertyPlaceholderConfigurer实例装配的问题
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1. 默认情况下,使用PropertyPlaceholderConfigurer多实例装配出现异常
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;
}
}
2. 如何装配能不出异常
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?
3. 如何解决占位符未配置的检查问题?不完美
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。
4.使PropertyPlaceholderConfigurer多实例装配出现异常对应的spring的代码在哪里
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)。