spring-boot-configuration-processor is not working on maven submodule project - maven

Question

I have a maven multi module project with one parent and three child modules.
The application uses spring boot. In one of the child modules, I have the SpringBootApplication:
#SpringBootApplication
#EnableConfigurationProperties({AppProperties.class})
public class MainSpringBootApplication {
public static void main(String[] args) {
SpringApplication.run(MainSpringBootApplication.class, args);
}
}
The App Properties are in the same module:
#Data
#ConfigurationProperties(prefix = "asdf")
public class AppProperties {
...
}
In the pom.xml of that module there is a dependency for the spring-boot-configuration-processor:
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-configuration-processor</artifactId>
<optional>true</optional>
</dependency>
Now the problem is, when I run mvn install on the parent project, the target/classes/META-INF/spring-configuration-metadata.json
file within this child module is not created. When I modify the pom of that child module to directly inherit from:
<parent>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-parent</artifactId>
<version>1.2.3.RELEASE</version>
<relativePath/> <!-- lookup parent from repository -->
</parent>
and do mvn install directly on the child module, the target/classes/META-INF/spring-configuration-metadata.json file is generated.
Do you have any hints?

Answer 1

There are two options I am aware of.
First one is my favourite (especially because it configures the order of APT libraries - the order of code generation).
But based, say, on the IDE auto-discovery mechanism, the 2nd one is also a good bet.
Both ones are primarily targeting the minimum size of the final artefact (dependencies' scope), which, for me is very important.
Not to increase the deliverable/archetype size with useless dependencies (apt libraries are needed only at compile time) is very important in the era of k8s/docker/cloud (resource efficiency).
So, without further ado, the options:
Use APT libraries only in maven compiler plugin configuration (nothing in dependencies).
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<version>${maven-compiler-plugin.version}</version>
<configuration>
<annotationProcessorPaths>
<path>
<groupId>org.projectlombok</groupId>
<artifactId>lombok</artifactId>
<version>${lombok.version}</version>
</path>
<path>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-configuration-processor</artifactId>
<version>${spring-boot.version}</version>
</path>
</annotationProcessorPaths>
</configuration>
</plugin>
This option is useful for the case the maven-compiler-plugin is not configured in plugins/pluginsManagement (but probably by means of its properties).
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-configuration-processor</artifactId>
<scope>provided</scope>
</dependency>
<dependency>
<groupId>org.projectlombok</groupId>
<artifactId>lombok</artifactId>
<scope>provided</scope>
</dependency>
Notes:
For option 2, scope provided is important, because it will allow to use the APT during the compilation but won't be included in the final artefact).
On the other hand (back to your question), in order to generate documentation in target/classes/META-INF/spring-configuration-metadata.json from the java doc, for lombok based java classes, you need these as well (#Getter and #Setter - are both needed).
#Setter
#Getter
#ConfigurationProperties(prefix = "asdf")
public class AppProperties {
/**
* foo - Should not be null or empty.
*/
private Map<String, String> foo;
and the following maven compiler plugin configuration as property (or in the plugin configuration).
<maven.compiler.parameters>true</maven.compiler.parameters>
After the compilation the IDE will parse the spring-configuration-metadata.json file and offer suggestion/quick doc/autocomplete in application.properties/application.yml.
Kr

Answer 2

I explicitly added:
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.8.0</version>
<configuration>
<annotationProcessorPaths>
<annotationProcessorPath>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-configuration-processor</artifactId>
<version>2.1.5.RELEASE</version>
</annotationProcessorPath>
</annotationProcessorPaths>
</configuration>
</plugin>
to the plugins section of the pom of the child module containing the #ConfigurationProperties annotated class. Now target/classes/META-INF/spring-configuration-metadata.json is generated.