I have a Java 11 project embedding Tomcat:

<dependency>
  <groupId>org.apache.tomcat.embed</groupId>
  <artifactId>tomcat-embed-core</artifactId>
  <version>10.1.0</version>
</dependency>

The Tomcat-specific code is in a subproject with only two classes. When I compile using Maven 3.8.6 and Java 17 using -Xlint:all, I see the following warning for that subproject:

[WARNING] Cannot find annotation method 'value()' in type 'aQute.bnd.annotation.spi.ServiceConsumer': class file for aQute.bnd.annotation.spi.ServiceConsumer not found

Doing a bit of searching brings up similar (but not exact) things, such as Lombok Issue #2145, which hints that I may need to add some sort of extra dependency such as biz.aQute.bnd:bndlib or org.osgi:osgi.annotation. But even after adding those dependencies, the warning remains.

Where is this error coming from, and what does it mean? I don't have any @ServiceConsumer annotation in my source code, and I couldn't find any in the Tomcat classes I'm extending, either. How can I make it go away?

I filed Tomcat Bug 66299.

CodePudding user response：

I discussed this on the Tomcat users mailing list [email protected] (thanks Mark), and here's what is happening:

• Tomcat effectively has two builds:
  1. What I call the Tomcat "primary build" uses Ant with build.xml, which compiles the source files, creates all the JARs and binaries, and publishes them to Maven Central (Nexus).
  2. Any "secondary build" by third parties using the published JARs and POMs, using e.g. org.apache.tomcat.embed:tomcat-embed-core:10.1.0 with Maven.
• The latest versions of direct dependencies are found in the Tomcat repository inside build.properties.default.
• The primary build generates JPMS and OSGi metadata, so some classes are annotated with the bnd annotation aQute.bnd.annotation.spi.ServiceConsumer. Currently Tomcat gets this annotation from biz.aQute.bnd:biz.aQute.bnd:6.3.1, which is apparently some aggregate JAR; the same annotation can be found in the smaller biz.aQute.bnd:biz.aQute.bnd.annotation:6.3.1.
• The aQute.bnd.annotation.spi.ServiceConsumer annotation source code uses the OSGi annotation org.osgi.annotation.bundle.Requirement. Currently this annotation can be found in org.osgi:osgi.annotation:8.1.0.
• The bnd and OSGi annotations remain part of the compiled classes even though they are not used at runtime and are not technically needed in any secondary builds.
• If you want to inform Maven and javac where these classes are so that they will not appear missing (if you are compiling with some variations of -Xlint), but that they nevertheless will not be needed at runtime (and technically aren't even needed at compile time in a secondary build) and should not be distributed in the resulting JAR, you can note them in your pom.xml file using the provided scope.

<dependency>
  <groupId>biz.aQute.bnd</groupId>
  <artifactId>biz.aQute.bnd.annotation</artifactId>
  <version>6.3.1</version>
  <scope>provided</scope>
</dependency>

<dependency>
  <groupId>org.osgi</groupId>
  <artifactId>osgi.annotation</artifactId>
  <version>8.1.0</version>
  <scope>provided</scope>
</dependency>

Maven will download these artifacts during your build thereby removing the warning, but they will not be included in the resulting artifacts of your build.