Slf4j: Found slf4j-api dependency but no providers were found

Question

I use Lombok. Some time ago when building a project, the compiler started issuing the following message:

Found slf4j-api dependency but no providers were found. Did you mean to add slf4j-simple? See https://www.slf4j.org/codes.html#noProviders .

If you follow the link, there is a rather vague comment:

This warning, i.e. not an error, message is reported when no SLF4J providers could be found on the class path. Placing one (and only one) of slf4j-nop.jar slf4j-simple.jar, slf4j-log4j12.jar, slf4j-jdk14.jar or logback-classic.jar on the class path should solve the problem. Note that these providers must target slf4j-api 1.8 or later.

In the absence of a provider, SLF4J will default to a no-operation (NOP) logger provider.

Please note that slf4j-api version 1.8.x and later use the ServiceLoader mechanism. Earlier versions relied on the static binder mechanism which is no longer honored by slf4j-api. Please read the FAQ entry What has changed in SLF4J version 1.8.0? for further important details.

If you are responsible for packaging an application and do not care about logging, then placing slf4j-nop.jar on the class path of your application will get rid of this warning message. Note that embedded components such as libraries or frameworks should not declare a dependency on any SLF4J providers but only depend on slf4j-api. When a library declares a compile-time dependency on a SLF4J provider, it imposes that provider on the end-user, thus negating SLF4J's purpose.

I have no idea how to do it correctly. If you have an experience, please, explain me how to do it.

Answer 1

As stated in tutorialspoint :

SLF4J stands for Simple Logging Facade for Java. It provides a simple abstraction of all the logging frameworks. It enables a user to work with any of the logging frameworks such as Log4j, Logback, JUL (java.util.logging), etc. using single dependency.

This means that you have to provide a concrete java logging library on your classpath on top of the dependency for SLF4J itself (Example with Maven):

<!-- https://mvnrepository.com/artifact/org.slf4j/slf4j-api -->
<dependency>
    <groupId>org.slf4j</groupId>
    <artifactId>slf4j-api</artifactId>
    <version>2.0.0-alpha0</version>
</dependency>

You will also need to specify the dependency on your preferred logging library. For instance:

For standard jdk1.4 logging :

 <!-- https://mvnrepository.com/artifact/org.slf4j/slf4j-jdk14 -->
<dependency>
    <groupId>org.slf4j</groupId>
    <artifactId>slf4j-jdk14</artifactId>
    <version>2.0.0-alpha0</version>
    <scope>runtime</scope>
</dependency>  

For slf4j-simple logging :

<!-- https://mvnrepository.com/artifact/org.slf4j/slf4j-simple -->
<dependency>
    <groupId>org.slf4j</groupId>
    <artifactId>slf4j-simple</artifactId>
    <version>2.0.0-alpha0</version>
    <scope>runtime</scope>
</dependency>

For log4j logging :

<!-- https://mvnrepository.com/artifact/org.slf4j/slf4j-log4j12 -->
<dependency>
    <groupId>org.slf4j</groupId>
    <artifactId>slf4j-log4j12</artifactId>
    <version>2.0.0-alpha0</version>
    <scope>runtime</scope>
</dependency>