[ERROR] class file for org.apache.logging.log4j.Logger not found

[DennisYudin]

Hi there i've got some troubles with log4j2 and I hope someone will help me.

Here's a thing.
I've got a small multi-module jakartaEE project and I'm getting Compilation failure which says:

error: cannot access Logger
[ERROR] class file for org.apache.logging.log4j.Logger not found

This happends when I try to compile one of my module.

The Idea is simple I've got a log4j2 wrapper in one module which looks like this:

public class Log4jHelper implements LogHelper {
	private static final String TR_EXT_ID_NAME = "[extTrId: %d] ";
	private static final String TR_ID_N_EXT_ID_NAME = "[trId: %d, extTrId: %d] ";
	private static final String TR_ID_NAME = "[trId: %d] ";

	private static final Map<Class<? extends Throwable>, Level> exceptions = new ConcurrentHashMap<>();

	private final Logger log;

	private Log4jHelper(Logger log) {
		this.log = log;
	}
	public static LogHelper getLogger(Class<?> clazz) {
		return new Log4jHelper(LogManager.getLogger(clazz));
	}
	public static LogHelper getLogger(Logger log) {
		return new Log4jHelper(log);
	}
	public static void registerException(Class<? extends Throwable> clazz, Level level) {
		exceptions.put(clazz, level);
	}
	@Override
	public void debug(Long trId, Long extTrId, String msg, Object... params) {
		log(Level.DEBUG, trId, extTrId, null, msg, params);
	}
   // and other methods

I added module with logging as dependecy to another module where I wanna use it

 <dependency>
            <groupId>com.packt.cookbook.libraries</groupId>
            <artifactId>common</artifactId>
            <version>${project.version}</version>
        </dependency>

and after that Im trying to use it

@Path("members")
@RequestScoped
public class MemberRESTService {

	private static final LogHelper log = Log4jHelper.getLogger(MemberRESTService.class);
	@Inject
	private Validator validator;
	@Inject
	private MemberRepository repository;
	@Inject
	private Registration registration;

	@PostConstruct
	public void init() {
		log.info("WEB module: logging is working...");
	} 

and when I run mvn clean compile command Im getting Compilation failure.

When I add to the pom of my second module log4j-api dependency, problem is gone.

<dependency>
            <groupId>org.apache.logging.log4j</groupId>
            <artifactId>log4j-api</artifactId>
            <scope>provided</scope>
        </dependency>

But when I run mvn dependency:analyze I can see the message:

Unused declared dependencies found:
[WARNING]    org.apache.logging.log4j:log4j-api:jar:2.23.1:provided

I think is not OK.

[Project repo: ]https://github.com/DennisYudin/simple-ear-jakartaee10

I would appreciate for any help!

[vy]

@DennisYudin, AFAICT, your library (i.e., LogHelper) explicitly refers to Log4j API dependencies, and hence, log4j-api should be a compile dependency, not provided.

Unless you already did, you might want to check Installation and Integrating with Jakarta EE pages.

[DennisYudin]

I forgot to mention that Im deploying on Wildlfy and it already provides the implementation for that and that's why the scope is provided I don't wanna make my EAR bigger.

Does it change anything?

[vy]

Not really. If you explicitly refer to a library — which you do via LogHelper — you need to have it in your compile class path.

[ppkarwasz]

Your Log4jHelper class leaks Log4j API types in the public API (for example in getLogger(Logger log)), therefore log4j-api is required during compilation. If you remove them from the public API, compilation should work.

Maven doesn't have a scope to describe a situation, when a transitive dependency is not needed at runtime, but only during compilation, but other build systems have it. For example Gradle has the compileOnlyApi configuration.