How to println to console log from jenkins shared library class

log-to-console-from-shared-lib-class.groovy

/*
 * If you develop a jenkins shared library, you might eventually face the issue described at:
 * https://stackoverflow.com/questions/47320406/propagating-logs-in-shared-library-to-jenkins-job-console
 * 
 * Many across the internet suggest to pass the "steps" object to the class as some (constructor) parameter, such as in
 * https://www.jenkins.io/doc/book/pipeline/shared-libraries/#accessing-steps
 * 
 * ... which works, however this might be difficult if there are many usages of the class where you "just" want to print something to
 * the console, maybe just for some debugging purposes. Unfortunatelly standard java Logger (in the momemnt of writing this gist at least) 
 * does not work. A not so nice, however working solution can be the following.
 */

// create a Utility class with a static Closure called "log":
class JenkinsUtils {

    static Closure<Void> log = { throw new RuntimeException("Logger not configured") }

}


// then, in your pipeline script you assign a sensible valie to it. You should do this in a @NonCPS block (see google for the reason).
// jenkins.groovy:

@NonCPS
def setupLogging() {
    JenkinsUtils.log = { String msg-> println msg }
}

def call() {
  ...
  setupLogging()
  ...
}

// then, in your widely used shared library class you can use this static closure without further ado:
class RestClient {

  void doStuff() {
    JenkinsUtils.log("...")
  }
  
}