Spring boot could not resolve placeholder in string

Karan :

I am running spring-boot on an embedded tomcat server through maven with mvn clean install spring-boot:run. But every time I run it I get this error:

 Caused by: java.lang.IllegalArgumentException: Could not resolve placeholder 'language' in string value "${language}"
    at org.springframework.util.PropertyPlaceholderHelper.parseStringValue(PropertyPlaceholderHelper.java:174) ~[spring-core-4.3.6.RELEASE.jar:4.3.6.RELEASE]
    at org.springframework.util.PropertyPlaceholderHelper.replacePlaceholders(PropertyPlaceholderHelper.java:126) ~[spring-core-4.3.6.RELEASE.jar:4.3.6.RELEASE]
    at org.springframework.core.env.AbstractPropertyResolver.doResolvePlaceholders(AbstractPropertyResolver.java:236) ~[spring-core-4.3.6.RELEASE.jar:4.3.6.RELEASE]
    at org.springframework.core.env.AbstractPropertyResolver.resolveRequiredPlaceholders(AbstractPropertyResolver.java:210) ~[spring-core-4.3.6.RELEASE.jar:4.3.6.RELEASE]
    at org.springframework.context.support.PropertySourcesPlaceholderConfigurer$2.resolveStringValue(PropertySourcesPlaceholderConfigurer.java:172) ~[spring-context-4.3.6.RELEASE.jar:4.3.6.RELEASE]
    at org.springframework.beans.factory.support.AbstractBeanFactory.resolveEmbeddedValue(AbstractBeanFactory.java:831) ~[spring-beans-4.3.6.RELEASE.jar:4.3.6.RELEASE]
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:1086) ~[spring-beans-4.3.6.RELEASE.jar:4.3.6.RELEASE]
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:1066) ~[spring-beans-4.3.6.RELEASE.jar:4.3.6.RELEASE]
    at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:585) ~[spring-beans-4.3.6.RELEASE.jar:4.3.6.RELEASE]
    at org.springframework.beans.factory.annotation.InjectionMetadata.inject(InjectionMetadata.java:88) ~[spring-beans-4.3.6.RELEASE.jar:4.3.6.RELEASE]
    at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor.postProcessPropertyValues(AutowiredAnnotationBeanPostProcessor.java:366) ~[spring-beans-4.3.6.RELEASE.jar:4.3.6.RELEASE]
    ... 35 common frames omitted

That error is regarding these two lines of code:

@Value("${language}")
private String language;

That language flag is specified in my application.properties like this:

application.properties

language=java
logging.level.org.springframework=TRACE

This is the confusing part: When I run the build without the spring-boot:run command, it builds properly and I can run the built jar with no issues at all. It is only when I try to run on the embedded tomcat server I run into this issue.

I can sort of bypass this by doing this in my code:

@Value("${language:java}")
private String language;

But that doesn't make sense to me since spring is supposed to read the default value from the application.properties file automatically.

EDIT: as people have pointed out, it is not reading application.properties at all when run on the embedded tomcat server. Any way to force it to read the file or a reason why it may not be reading it? It works fine when deployed to an external app server instead of the embedded one.

Thanks in advance for your help.

Karan :

Fixed by adding these lines to the pom under the <resources> section

<resource>
     <directory>src/main/resources</directory>
     <filtering>true</filtering>
     <includes>
          <include>**/*.properties</include>
     </includes>
</resource>

What I don't fully understand is the need for doing this.

a) I can run this on an external app server without having to add this line and the app reads application.properties just fine.

b) I can run the app as a standalone java application in eclipse (i.e., without having to build the app through maven) and it reads application.properties just fine

c) isn't spring-boot supposed to read it by default regardless? (as shown by the two cases above?)

Thanks everyone for their help. hopefully this will help others.