Gradle artifactory plugin saying "Cannot cast object 'org.jfrog.gradle.plugin.artifactory.dsl.ArtifactoryPluginConvention'..."

The problem was that when I added the various bits to the sibling project that meant I had two projects defining the buildscript {} section.

buildscript {
    ...
    dependencies {
        classpath group:'org.jfrog.buildinfo', name: 'build-info-extractor-gradle', version: '3.0.1'
    }
}

Apparently that caused two different versions of the dependency to exist in the classpath, hence the error.

The solution was to move the buildscript bit into the master project so those dependencies are only defined once:

buildscript {
    repositories {
        maven { url "https://plugins.gradle.org/m2/" }
    }
    dependencies {
        classpath group:'org.jfrog.buildinfo', name: 'build-info-extractor-gradle', version: '3.0.1'
    }
}

Here's another potential cause. All of this looks to be a problem with rival classloaders defining the class. The full qualified classes include the loader. so, load A foo.bar is not loader B foo.bar and crossing that divide is a complex dance requiring interfaces and careful definition.

So, when using the Jenkins artifactory plugin to build your gradle project with the gradle artifactory plugin, you must add the usesPlugin or jenkins plugin will generate an init script which adds the gradle plugin on to a class loader.

def server = Artifactory.server "artifactory"
def rtGradle = Artifactory.newGradleBuild()
rtGradle.usesPlugin = true // Artifactory plugin already defined in build script
...

My problem was, desktop build OK, jenkins build shows this post's problem

I was getting a similar exception when building with Jenkins. For me the conflict was with Jenkin's version and the version in the Build script:

To address this the Artifactory section of the build has a flag you can check specifying that you want to use the version from the gradle file:

This fixed my issue. Hope it helps.