Why does currentBuild.build().getActions(ParametersAction).get(0) return default parameter values rather the specified values in Jenkins pipeline?

Question

I'm trying the change a parameter value in a Jenkins pipeline. Here's my latest script code:

// Replace spaces in PROJECT_NAME parameter with dashes
script {
    def build = currentBuild.build()
    def parms = build.getActions(ParametersAction).get(0)
    for (ParameterValue parm : parms.getParameters()) {
        StringBuilder msg = new StringBuilder()
        msg.append(parm.getName())
        msg.append(": ")
        if (parm.getValue() == null) {
            msg.append("<null>")                           
        } else {
            msg.append(String.valueOf(parm.getValue()))   
        }
        print(msg)
    }
    def projectNameWithoutSpaces = new StringParameterValue("PROJECT_NAME", "${params.PROJECT_NAME}".replaceAll(" ", "-"))
    build.replaceAction(parms.createUpdated(Arrays.asList(projectNameWithoutSpaces)))
}

I'm finding that parms contains the default parameter values rather than the values specified in the pipeline build. This, in turn, is causing build.replaceAction(parms.createUpdated(Arrays.asList(projectNameWithoutSpaces))) to replace all parameter values except for the PROJECT_NAME value with the parameter's default value.

Why does parms contain default parameter values rather than the values specified in the pipeline build? How do I get the specified parameter values so that I can correctly change the value of the PROJECT_NAME parameter?

Answer 1

This was a user error on my part; currentBuild.build().getActions(ParametersAction).get(0) does return the correct parameter values. It turns out that one of my earlier failed attempts had set all of my pipeline's parameter values, except for the PROJECT_NAME parameter value, to their default values.

One side effect of using build.replaceAction() is that it actually changes the pipeline build's PROJECT_NAME parameter value in the Jenkins web client. So when I go to do a rebuild, the PROJECT_NAME parameter has the update value (spaces replaced with dashes), which is really not what I want.

Also, early on I tried the simpler solution of simply setting params.PROJECT_NAME to the new value:

// Replace spaces in PROJECT_NAME parameter with dashes
script {
    params.PROJECT_NAME = "${params.PROJECT_NAME}".replaceAll(" ", "-")
}

However, this failed with an java.lang.UnsupportedOperationException as the params object is backed by java.util.Collections$UnmodifiableMap.

I wasn't aware that the pipeline parameters values are also available via the env object (thanks to zett42 for pointing this out). So I tried setting env.PROJECT_NAME:

// Replace spaces in PROJECT_NAME parameter with dashes
script {
    env.PROJECT_NAME = "${env.PROJECT_NAME}".replaceAll(" ", "-")
}

This worked just fine without changing the pipeline build's PROJECT_NAME parameter value in the Jenkins web client.