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There's Lombok annotation #Slf4j which won't work

I need your help. I have a problem with Lombock annotation #Slf4j. When I try to use it I don't have ability to use its functionality:
There's my build.gradle file:
I've already installed Lombock into my IntelliJ Idea and enabled Annotating processing, but it haven't got me resul yet.
Can you make some advice? I would be very grateful!

Taking a wild stab here, but lombok doesn't include slf4j. It really can't do that1. All features in the extern packages work like this, and it is why the lombok.extern package layer exists: To show you that it's a lombok feature that makes some non-core ('external') dependency work nicer, not that the lombok feature includes this dependency or replaces it.
Thus, all you would need to fix this is to add slf4j to your dependencies:
compile 'org.slf4j:slf4j:1.7.31'
omr something along those lines. Note that SLF4j also needs runtime configuration (slf4j itself is just a 'frontend' that lets you write log statements that go to whereever your configuration says they go at runtime. This 'configuration' includes the code to actually do stuff with these logs. Slf4j tutorials will cover all this.
[1] Adding the deps automatically is not really possible; lombok ships with a number of features that are specifically to make some library / framework easier to use, we (DISCLAIMER: I do quite a bit of work on lombok) can't ship them all of those as deps of lombok, and we haven't (and probably would never) try to hack into your build system to make some sort of semi-dependent system where we detect you use e.g. #Slf4j and somehow make your build system include it only then.

There is some IDE build issue you have.
Why don't you adopt Maven (or Gradle) build tool, that is used in maybe 80% (gradle is maybe other 19.99%) team projects.
And then there is nothing specific about using Lombock
https://projectlombok.org/setup/maven
just
<dependencies>
<dependency>
<groupId>org.projectlombok</groupId>
<artifactId>lombok</artifactId>
<version>1.18.20</version>
<scope>provided</scope>
</dependency>
</dependencies>
And it works in any IDEA or most IDE
P.S. Specifically no configuration/plugin in IDEA since v2020.3
https://projectlombok.org/setup/intellij
P.P.S. If you use maven/gradle and have any issues in any IDE,
try first to make sure, that there is no issues with build itself by running in command line
mvn package
or
gradle build
And then if build is OK, try to resolve specific IDE issue.
Think like "what most people do or won't do to make it work"
For example you can install one more the newest IDEA instance, e.g. IDEA CE (that it undervalued, as it is free) and open your project there: it should just work without any dancing.

How to add a dependency to module path?

I am very new to programming, and while working on my first software development project I came across the error: "package javax.activation is not visible." I have read other posts that have said that in order to fix the error, one must add a dependency to the module path?
Because I'm just starting out, I really don't know what this means and how to go about that, and was wondering if someone could point me in the right direction? Thanks in advance. (I'm also using JGrasp if that matters)

Broadly speaking, a dependency is code (often written by someone else) which your application needs to compile.
A dependency in your case, is a java library which has classes that need to be on your class path. You can find more about class paths here: https://docs.oracle.com/javase/tutorial/essential/environment/paths.html. In order to overcome error mentioned in a question, you need to have javax.activation module dependency on your class path.
You could do it in few ways. In the majority of IDEs (in your case we are talking about JGrasp) there is a way to add a dependency to the project directly. Then, your IDE would compile the code with given dependency on a class path and problem would be solved. And that would be the first and most beginner-friendly way, unfortunately I haven't a faintest idea about JGrasp so I'm going to focus on other solutions.
The second way you could do this is to build your program with build automation tool, such as Apache Maven or Gradle. You should definitely check those guys out, as they are insanely useful when it comes to building Java code and, sooner or later, you will probably start using them anyway. Let's say you have chosen Apache Maven. In your project you would then have a pom.xml file and you would simply look-up the needed dependency in Maven Central repository, add it to your dependencies section in pom.xml file and build the application. Your pom would look something like this:
<project>
...
<dependencies>
<!-- https://mvnrepository.com/artifact/javax.validation/validation-api -->
<dependency>
<groupId>javax.validation</groupId>
<artifactId>validation-api</artifactId>
<version>2.0.1.Final</version>
</dependency>
</dependencies>
...
</project>
Of course Apache Maven is not a lightweight tool so you would have to take some time to learn how to build code with it. I recommend starting with this tutorial:
https://maven.apache.org/guides/getting-started/maven-in-five-minutes.html
I also encourage you to get your hands on Apache Maven docs, as it is quite readable and transparent.
And the last way I can think of is to manually compile your application and include the required dependency during the compilation process. There are plenty of tutorials on SO that tell you how to do this, so I'll simply summarize and indicate the resources. What you need to do is to find the required dependency jar package. You will want to search the maven central repository (see: https://mvnrepository.com/) and from there download your .jar file. The next thing you need to do is to learn how to compile your Java code to .class files including the downloaded jar. To acquire such a wonderful skill, please see this one: How to include jar files with java file and compile in command prompt
Amongst those three ways, the recommended one is to get to know with build tools such as Apache Maven or Gradle. Hope I helped you! Good luck

Can I add maven dependencies that are packed as anything other than .jar?

I just produced my first parent-module project with maven, and successfully installed it. Can I add this project as a dependency in another project, only by referring to the parent? My Eclipse IDE complains that it can't find the parent.jar, but that is not a surprise, as it is packaged as parent.pom.
Question:
So is it possible to add a parent (.pom) dependency, and get all transitive dependencies for free, or do I have to add .jar's.
Bonus Question:
Is it possible to add dependencies to other packaging formats as well, like a war? I can't really figure out how that would work, or why I would need that at this point though. Just curious.
Disclaimer:
I'm still learning maven, and find the philosophy and theory of it to be great. However, there are so many pits and reefs that seems to pop out, and more than once, I struggle to see if I'm trying to do something impossible, or if there is another mistake in configurations I.E. Right now Eclipse says it can't find any of my .m2 referenced dependencies in this one particular project. I have no idea why, as other projects works fine. I am in other words trying to find the error, by checking one area at the time...

Answer: Yes, you can add different types such as pom, test-jar and so on. Jar is just the default
Bonus Answer: Yes, you can specify type war as well
The Maven-Guide defines the following types: "The current core packaging values are: pom, jar, maven-plugin, ejb, war, ear, rar, par."
Here is a example on how a POM is included:
<dependencies>
<dependency>
<groupId>com.my</groupId>
<artifactId>comm-group</artifactId>
<type>pom</type>
</dependency>
</dependencies>
This (the pom of comm-group) is oftenly used to group certain dependencies and include all of them using the type-pom.
Here is additional information on grouping: http://blog.sonatype.com/2009/10/maven-tips-and-tricks-grouping-dependencies/#.VFC7LR_JY8c Note that there are similar behaviours you could create using polymorphism.
I had my issues with maven when we migrated from Ant and i still have certain concernes on it (like were is the advantage of maven if 80% of our SWEs apply wrong scopes, types and so on leading to a massive drawback if they just 'need to add a fcking jar' as well as to refactorings lead by "maven gurus").
BUT: I can guarantee you that if you go throught http://maven.apache.org/pom.html completely you will aquire statisfieing results compared to ANT over time.
Update: I just ran into the case where my pom could not be included on the remote build server while it worked building it from inside Intellij Idea/ Eclipse. Type definition in my case had to be lowercase (e.g. 'pom' instead of 'POM').

Which JAR does Java pick for a certain import?

Dependency issues, we've all dealt with them, but I'm mostly used to C# and now working in Java so I have some questions.
Let's say I add a library to my project, called ExtLib.
ExtLib has a certain library included in its lib-folder, let's call it LogLib-1.0.
I'm using Eclipse and I've made a User Library for ExtLib, included its main jar file and all of the files in its lib-folder. So far so good.
But now I want to do some logging of my own, so I make another User Library and add the newer LogLib-1.1 to it, because it has some new features I want to use.
Can I ever be sure I'm not breaking ExtLib this way?
I know .NET uses the Global Assembly Cache and methods like that, but I have no clue how Java handles this. I tried Googling, but didn't find much, a few mentions of the Classloader here and there, but nothing helpful.
Can anyone tell me what a proper way to deal with this issue is? Or is it no issue at all?

In this specific case (LogLib-1.0 and LogLib-1.1) we're dealing with the same library that is both a direct dependency of your application, and a "transitive" dependency via the ExtLib. In this situation, dependency management can come to help.
It will probably reason that LogLib-1.1 is a backward compatible release of LogLib-1.0, and it will decide that your application can run fine using only LogLib-1.1.
In the Java world, tools like Maven, Gradle or SBT exist to help you in this. Maven is the most widespread, and other tools often are compatible with Maven.
Usage
To solve this situation using Maven, you would add a file called pom.xml to your application, stating it depends on LogLib version 1.1. That might look like this (note that this example is pure fiction):
<dependency>
<groupId>org.loglib</groupId>
<artifactId>loglib</artifactId>
<version>1.1</version>
</dependency>
The ExtLib you're using also has a pom.xml shipped with it, and it might state
<dependency>
<groupId>org.loglib</groupId>
<artifactId>loglib</artifactId>
<version>1.0</version>
</dependency>
Maven (or any other tool) would decide that including LogLib-1.1 is sufficient to get your application running. When using Maven, mvn depedency:tree helps you visualise that.
Deployment
With respect to the packaging / deployment question: mvn package will package your application to a jar, war or ear archive, including only the dependencies you need (and not two versions of the same lib). This makes you don't have to worry about the order in which your application server reads the jar files.

How to edit snapshot dependencies

I am very new to the industry, so apologies in advance for the very likely stupidity of the question.
In the team, we work with Intellij IDEA 13 as IDE, and use Maven 3 for our projects. We provide a few online services and portals, and I'm just starting to work on one: the project has several dependencies that are shared by other older projects, some are JAR archives, some are WARs...
To my questions re: how to edit those dependencies locally (e.g. editing a resources.properties was the case I had in mind) my tutor suggested turning the dependencies into snapshots and work with those.
What I managed to do was create a copy of the appropriate folders in my local repository and change wherever the version of the dependency was in the name or in the files, then modify my pom.xml files.
Now, this works perfectly if I open the JAR/WAR and edit some file, but I'd like to be able to do it from my IDE, also cause not being able to suggests I'm probably doing this in a wrong way. Do I need to somehow unpack the dependency to be able to do so? Is my entire approach wrong?
P.S.: I would ask someone in my office, but oddly enough none of those who could help are at work today anymore!

If none of your colleagues was able to help you, I am afraid there might be something else hidden.
However, let's try it!
I am guessing, here, that your resources.properties is a part of his own project. Project handled by Maven and expressed as a dependency in one of your main project.
I am also guessing that your main projects are WARs (Webapps mostly, services, portals) and the JARs are libraries, configurations, etc...)
Therefore, I am guessing that your webapps are referencing some libraries as Maven dependencies, to a specific version.
That said, IntelliJ (and other IDE) can easily handle modification of either JARs and WARs related to each other via Maven as long as the visioning is meaningful.
Note: Having -SNAPSHOT at the end of the version number tell to Maven NOT to cache the package. On the opposite, a definitive version number is considered as released and is only fetched from the cache. This is important because with a SNAPSHOT, you can publish an illimited number of time and it is guaranteed to have the latest version.
Note: Doing mvn clean install publish a package into your local Maven repository (generally located in ~/.m2) and is only available to you.
The general good practice is to have, in all the development branches of your DVCS, all your owned, often modified projects (Don't be too greedy, it depend on the situation) as SNAPSHOT. And during a release (Maven has a specific plugin for that) change all the versions to a final one, attributed in this precise moment (You never know if you will need a minimal version or a major).
Your code, then, has always the SNAPSHOT number of your expected next release.
Finally, I think that in your case, if you choose to change the pom.xml of one of your library for a SNAPSHOT, you should change the pom.xml of the root project to correspond.
If this dependency version is the same, then, you can add your library as a module within IntelliJ and the IDE will do the math to figure that the Maven dep and the Java module are the same entity.
I don't even know if that's help you (I'm not even sure if it's clear), but I hope it will make you ask more questions about what you need. Your co-workers will probably be able to help you more.