[FIXED] Spring boot could not resolve placeholder in string

Issue

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.

Solution

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.

Answered By - Karan
Answer Checked By - Mary Flores (JavaFixing Volunteer)