Unable to read meta-data for class. Spring autoconfig

Scenario

Let’s say you are building a spring-boot library and would like to tap into spring-boot auto-configuration feature. You create class MyAutoConfiguration and annotate it with the spring @Configuration annotation. Then, in you application, you use this library as a dependency, run the application and get the following exception

Caused by: java.lang.IllegalStateException: Unable to read meta-data for class com.mylib.autoconfigure.MyAutoConfiguration
    at org.springframework.boot.autoconfigure.AutoConfigurationSorter$AutoConfigurationClass.getAnnotationMetadata (AutoConfigurationSorter.java:233)
    at org.springframework.boot.autoconfigure.AutoConfigurationSorter$AutoConfigurationClass.getOrder (AutoConfigurationSorter.java:204)
    at org.springframework.boot.autoconfigure.AutoConfigurationSorter$AutoConfigurationClass.access$000 (AutoConfigurationSorter.java:150)
    at org.springframework.boot.autoconfigure.AutoConfigurationSorter.lambda$getInPriorityOrder$0 (AutoConfigurationSorter.java:63)

Steps to Reproduce

Create spring-boot project and add the following class

@Configuration
public class MyAutoConfiguration {
  private static final Logger LOGGER = LoggerFactory.getLogger(MyAutoConfiguration.class);

  @PostConstruct
  public void printConfigurationMessage() {
    LOGGER.info("Configuration for My Lib is complete...");
  }
}

Do not forget to add spring.factories file to resources -> META-INF -> spring.factories

spring.factories file looks like this:

org.springframework.boot.autoconfigure.EnableAutoConfiguration=com.mylib.autoconfigure.MyAutoConfiguration

maven file for this project may look something like this:

<parent>
  <groupId>org.springframework.boot</groupId>
  <artifactId>spring-boot-starter-parent</artifactId>
  <version>2.1.6.RELEASE</version>
  <relativePath /> <!-- lookup parent from repository -->
</parent>

<!-- Spring -->
<dependencies>
  ...
</dependencies>

<build>
  <plugins>
    <plugin>
      <groupId>org.springframework.boot</groupId>
      <artifactId>spring-boot-maven-plugin</artifactId>
    </plugin>
  </plugins>
</build>

Finally, you add your library as a dependency to your application, run it and get the runtime error mentioned above.

Diagnostic

Online search suggests that either spring.factories file is missing, or the name of the class is not correct, … Everything is checked out and fine. To make sure MyAutoConfiguration class is in fact included I start looking into my library jar:

jar tvf target/mylib.jar | grep MyAutoConfiguration

BOOT-INF/classes/com/mylib/autoconfigure/MyAutoConfiguration.class

Here, I can see that the class is under BOOT-INF/classes root.

Solution

Apparently, auto configuration classes cannot be found under BOOT-INF/classes root. The main issue with my setup was the fact that I used spring-boot-maven-plugin to build the library module. After removing the plugin and rebuilding the library jar tvf target/mylib.jar | grep MyAutoConfiguration is showing this:

com/mylib/autoconfigure/MyAutoConfiguration.class

Now, spring-boot application builds fine and MyAutoConfiguration class is found and ready to be used to configure library.

Scenario

Steps to Reproduce

Diagnostic

Solution

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