问题描述
我有以下配置文件：
@Configuration
public class PropertyPlaceholderConfigurerConfig {
@Value("${property:defaultValue}")
private String property;
@Bean
public static PropertyPlaceholderConfigurer ppc() throws IOException {
PropertyPlaceholderConfigurer ppc = new PropertyPlaceholderConfigurer();
ppc.setLocations(new ClassPathResource("properties/" + property + ".properties"));
ppc.setIgnoreUnresolvablePlaceholders(true);
return ppc;
}
}
我使用以下VM选项运行我的应用程序：
I run my application with following VM option:
-Dproperty=propertyValue
所以我想让我的应用程序在启动时加载特定的属性文件。但由于某些原因，在这个阶段 @Value 注释不处理，属性 null 。另一方面，如果我有 PropertyPlaceholderConfigurer 通过xml文件配置 - 一切正常工作。 Xml文件示例：
So I'd like my application to load specific property file on startup. But for some reason at this stage @Value annotations are not processed and property is null. On the other hand if I have PropertyPlaceholderConfigurer configured via xml file - everything works perfectly as expected. Xml file example:
<bean class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer">
<property name="ignoreResourceNotFound" value="true"/>
<property name="location">
<value>classpath:properties/${property:defaultValue}.properties</value>
</property>
</bean>
如果我尝试在另一个Spring配置文件中注入属性值，如果我将我的 PropertyPlaceholderConfigurer bean创建移动到该配置文件 - 字段值再次为null。
If I try to to inject property value in another Spring configuration file - it is properly injected. If I move my PropertyPlaceholderConfigurer bean creation to that configuration file - field value is null again.
作为解决方法，我使用这行代码：
As workaround, I use this line of code:
System.getProperties().getProperty("property", "defaultValue")
我想知道为什么会发生这种行为，也许可以用其他方式重写它，但是没有xml？
Which is also works, but I'd like to know why such behavior is occurs and maybe it is possible to rewrite it in other way but without xml?
推荐答案
从春天：
因此，您尝试在启用占位符处理所需的代码块中使用占位符。
So, you are trying to use a placeholder in the code block required to enable placeholder processing.
As @ M.Deinum提到，你应该使用一个PropertySource（默认或自定义实现）。
As @M.Deinum mentioned, you should use a PropertySource (default or custom implementation).
下面的示例显示如何在PropertySource注释中使用属性以及如何从PropertySource注入属性到字段中。
Example below shows how to use properties in a PropertySource annotation as well as how to inject properties from the PropertySource in a field.
@Configuration
@PropertySource(
value={"classpath:properties/${property:defaultValue}.properties"},
ignoreResourceNotFound = true)
public class ConfigExample {
@Value("${propertyNameFromFile:defaultValue}")
String propertyToBeInjected;
/**
* Property placeholder configurer needed to process @Value annotations
*/
@Bean
public static PropertySourcesPlaceholderConfigurer propertyConfigurer() {
return new PropertySourcesPlaceholderConfigurer();
}
}
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