Overriden application.yml in multi-module Spring Boot app

Question

There is a Spring Boot 2 app with such a structure:

parent-module
    module-1
        src
            main
                java
                resources
                - application.yml
    module-2
        src
            main
                java
                resources
                - application.yml

Also, module-1 depends on module-2, specified in pom.xml dependencies section.

The problem is that when I specify some properties in module-2's application.yml - they are not visible in main module-1's components (via @Value annotation).

As was answered here seems like module-1's application.yml overrides module-2's application.yml. There is a workaround - if I use name application.yaml in module-2 everything works fine, but I'm going to add more modules and, finally, it's dirty hack.

What I'm doing wrong? Should such an hierarchy of property files specified somehow? I will be happy to provide more details if it's needed.

Thank you!

Answer 1

Spring Boot is a runtime framework. I understand that your modules are not spring-boot applications by themselves (you can't make a dependency on a spring boot application packaged with spring boot maven plugin, because it produces an artifact that is not really a JAR from the Java's standpoint although it does have *.jar extension).

If so, they're probably regular jars. So you should have a "special" module that assembles the application. This special module lists both 'module1' and 'module2' in <dependency> section and should contain a definition of spring-boot-maven-plugin in its build section (assuming you're using maven). But if so you shouldn't really have more than one application.yml - it will be misleading. Instead, put the application.yml to the src/main/resources of that "special" module.

If you really have to for whatever reason work with multiple application.yaml files, make sure you've read this thread

Answer 2

application.yml is, as the name indicates, an application-level file, not a module-level file.

It is the build script that assembles the final application, e.g. the .war file, that needs to include a application.yml file, if any.

If modules need properties, and cannot rely on the defaults, e.g. using the : syntax in @Value("${prop.name:default}"), they need to provide a module-level property file using @PropertySource("classpath:/path/to/module-2.properties").

Note: By default, @PropertySource doesn't load YAML files (see official documentation), but Spring Boot can be enhanced to support it. See @PropertySource with YAML Files in Spring Boot | Bealdung.

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Alternative: Have the application-level build script (the one building the .war file) merge multiple module-level build scripts into a unified application.yml file.