Groovy script won't run due to NoClassDefFoundError

Question

I wrote a very simple groovy script to test if a cron expression is valid:

import hudson.scheduler.CronTabList

try {
    def cron = CronTabList.create("@daily")
    println("Valid cron!")
} catch(Exception e) {
    println("Invalid cron!")
    e.printStackTrace()
}

Running this fails with the message:

Caught: java.lang.NoClassDefFoundError: javax/servlet/ServletContextListener
java.lang.NoClassDefFoundError: javax/servlet/ServletContextListener
    at hudson.scheduler.BaseParser.<clinit>(BaseParser.java:149)
    at hudson.scheduler.CronTab.set(CronTab.java:113)
    at hudson.scheduler.CronTab.<init>(CronTab.java:100)
    at hudson.scheduler.CronTabList.create(CronTabList.java:121)
    at hudson.scheduler.CronTabList.create(CronTabList.java:96)
    at hudson.scheduler.CronTabList$create.call(Unknown Source)
    at validate_crontab.run(validate_crontab.groovy:7)
Caused by: java.lang.ClassNotFoundException: javax.servlet.ServletContextListener
    ... 7 more

Process finished with exit code 1

My build.gradle dependencies look like:

dependencies {
    compile 'org.codehaus.groovy:groovy-all:2.3.11'
    compile group: 'org.quartz-scheduler', name: 'quartz', version: '2.3.0'
    compile group: 'org.jenkins-ci.main', name: 'jenkins-core', version: '2.85'
    testCompile group: 'junit', name: 'junit', version: '4.12'
}

I simply can't figure out what's to blame and why I can't run the script.

Any help is much appreciated!

What application server are you using, and what IDE? The problem might be related to the build path that your server points to. — homersimpson, Jun 18 '18 at 14:43

Lachezar Balev · Accepted Answer · 2018-06-18T18:41:52.597

Apparently what you miss is the servlet API. For example:

dependencies {
    compile group: 'javax.servlet', name: 'javax.servlet-api', version: '3.1.0'
}

If you put that in your dependencies your script will most likely run.

But I guess that it is fairly important to understand why did you get this error. If you have a closer look at the jenkins-core library you will notice that it has a "provided" dependency to the servlet API. A provided dependency in simpler words means that the library (jenkins-core in your case) is compiled with the assumption that the servlet API jar will be present in the class path at your production environment - e.g. when using the lib in a web application running within a servlet container.

I guess that you run your groovy script as a standalone app, that is why you are getting an error. And... DISCLAIMER - I do not know if using jenkins-core in standalone apps is intended, though :-).

Groovy script won't run due to NoClassDefFoundError

1 Answers1