java - 在 spring 配置中使用属性

Question

我有一个属性配置取决于我的环境，像这样:

 <bean id="someConfigurer" 
       class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer">
    <property name="locations">  
        <list> 
            <value>classpath:properties/database.${my.env}.properties</value>
            <value>classpath:properties/morestuff.${my.env}.properties</value>
            [..]
        </list>  
    </property>
</bean>

现在我可以在我的项目中保留不同的属性文件，例如 database.prod.properties 或 database.qual.properties。如果我使用 -Dmy.env=foobar 启动我的应用程序，这很好用。

如果没有提供环境会怎样？由于 PropertyPlaceholderConfigurer 抛出的 FileNotFoundException，应用程序不会启动。我不想保留所有属性文件的副本作为后备。如果未设置系统属性，我想要的是将环境设置为后备。

我试图用第二个 PropertyPlaceholderConfigurer 来解决这个问题，例如:

<bean id="fallbackPropertyConfigurer"  
      class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer">
    <property name="locations">  
        <list>  
            <value>classpath:properties/default-env.properties</value>
        </list>  
    </property>
    <property name="order" value="0" />
    <property name="ignoreUnresolvablePlaceholders" value="true"/>
    <property name="systemPropertiesModeName" value="SYSTEM_PROPERTIES_MODE_OVERRIDE"/>
</bean>   

default-env.properties 仅包含一个属性:my.env=qual。

顺序设置为“0”以确保首先评估此 bean。我仍然收到以下异常:

DEBUG  o.s.c.e.PropertySourcesPropertyResolver - Searching for key 'my.env' in [systemProperties]
DEBUG  o.s.c.e.PropertySourcesPropertyResolver - Searching for key 'my.env' in [systemEnvironment]
DEBUG  o.s.c.e.PropertySourcesPropertyResolver - Could not find key 'my.env' in any property source. Returning [null]
DEBUG  o.s.b.f.s.DefaultListableBeanFactory - Finished creating instance of bean 'someConfigurer'
INFO   o.s.b.f.c.PropertyPlaceholderConfigurer - Loading properties file from class path resource [properties/default-env.properties]
INFO   o.s.b.f.c.PropertyPlaceholderConfigurer - Loading properties file from class path resource [properties/database.${my.env}.properties]
INFO   o.s.b.f.s.DefaultListableBeanFactory - Destroying singletons in org.springframework.beans.factory.support.DefaultListableBeanFactory@435a3a: defining beans [fallbackPropertyConfigurer,someConfigurer,[..],org.springframework.context.annotation.internalCommonAnnotationProcessor,org.springframework.context.annotation.ConfigurationClassPostProcessor$ImportAwareBeanPostProcessor#0]; root of factory hierarchy
Exception in thread "main" org.springframework.beans.factory.BeanInitializationException: Could not load properties; nested exception is java.io.FileNotFoundException: class path resource [properties/database.${my.env}.properties] cannot be opened because it does not exist
    at org.springframework.beans.factory.config.PropertyResourceConfigurer.postProcessBeanFactory(PropertyResourceConfigurer.java:87)
    at org.springframework.context.support.AbstractApplicationContext.invokeBeanFactoryPostProcessors(AbstractApplicationContext.java:681)
    [..]

如果我注释掉 PropertyPlaceholderConfigurer 以消除错误，我可以在其他 bean 中使用 %{my.env}。

任何人都可以解释这种行为吗？

Answer 1

您可以像这样设置默认值(在 Spring 3 中):

${my.env:qual}