Script to update all Jenkins jobs using old JDK to new JDK

update-all-jenkins-jobs-from-old-jdk-to-new.groovy

String oldJdkName = "JDK 1.7.0_80"
String newJdkName = "JDK 1.8.202"

boolean dryRun = true

Set jdks = new HashSet()
def newJdk = Jenkins.instance.getJDK(newJdkName)
assert newJdk, "unable to find a configured jdk named ${newJdkName}"

println "reconfiguring all jobs using ${oldJdkName} to use jdk '${newJdkName}'"

for (item in Jenkins.instance.getAllItems(Job.class).findAll{it.hasProperty('JDK')}) {
    if ( oldJdkName == item.JDK?.name ) {
        println "\t job '${item.name}' current jdk '${item.JDK?.name}', changing to ${newJdkName}"
        if (!dryRun) {
            item.setJDK(newJdk)
        }
    }
}