【SSM 错误 1】Could not resolve placeholder ‘driver‘ in string value “${driver}“

1. 错误信息

java.lang.IllegalStateException: Failed to load ApplicationContext
	at org.springframework.test.context.DefaultCacheAwareContextLoaderDelegate.loadContext(DefaultCacheAwareContextLoaderDelegate.java:94)
	unAfterTestClassCallbacks.evaluate(RunAfterTestClassCallbacks.java:68)
	4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:68)
	at com.intellij.rt.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:33)
	at com.intellij.rt.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:230)
	at com.intellij.rt.junit.JUnitStarter.main(JUnitStarter.java:58)
Caused by: org.springframework.beans.factory.BeanDefinitionStoreException: Invalid bean definition with name 'dataSource' defined in class path resource [spring/spring-dao.xml]: Could not resolve placeholder 'driver' in string value "${driver}"; nested exception is java.lang.IllegalArgumentException: Could not resolve placeholder 'driver' in string value "${driver}"
	tProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(PostProcessorRegistrationDelegate.java:162)
	org.springframework.test.context.support.AbstractDelegatingSmartContextLoader.delegateLoading(AbstractDelegatingSmartContextLoader.java:109)
	at org.springframework.test.context.support.AbstractDelegatingSmartContextLoader.loadContext(AbstractDelegatingSmartContextLoader.java:261)
	at org.springframework.test.context.DefaultCacheAwareContextLoaderDelegate.loadContextInternal(DefaultCacheAwareContextLoaderDelegate.java:68)
	at org.springframework.test.context.DefaultCacheAwareContextLoaderDelegate.loadContext(DefaultCacheAwareContextLoaderDelegate.java:86)
	... 24 more
Caused by: java.lang.IllegalArgumentException: Could not resolve placeholder 'driver' in string value "${driver}"
	org.springframework.beans.factory.config.BeanDefinitionVisitor.resolveStringValue(BeanDefinitionVisitor.java:282)
	at org.springframework.beans.factory.config.BeanDefinitionVisitor.resolveValue(BeanDefinitionVisitor.java:204)
	at org.springframework.beans.factory.config.BeanDefinitionVisitor.visitPropertyValues(BeanDefinitionVisitor.java:141)
	at org.springframework.beans.factory.config.BeanDefinitionVisitor.visitBeanDefinition(BeanDefinitionVisitor.java:82)
	at org.springframework.beans.factory.config.PlaceholderConfigurerSupport.doProcessProperties(PlaceholderConfigurerSupport.java:208)
	... 36 more

applicationContext 加载properties类型的配置文件的问题

2. 错误缘由

在配置文件中，使用 2 次引入配置文件的扫描，但是两次扫描的 key 是一样的，并不能进行两次扫描

<context:property-placeholder location="classpath:config/resouce.properties"/>
<context:property-placeholder location="classpath:config/db.properties"/>

3. 解决办法

方法1：将配置文件写到一个方法里，用 ,隔开

<context:property-placeholder location="classpath:config/db.properties,classpath:config/resouce.properties"/>

方法2：在每个扫描的配置文件后加上 ignore-unresolvable=“true”

<context:property-placeholder location="classpath:config/resouce.properties" ignore-unresolvable="true"/>
<context:property-placeholder location="classpath:config/db.properties" ignore-unresolvable="true"/>