Jenkins pipeline - How to iterate through a list

Question

I'm required to read values from a file in my pipeline. I'm using split() which puts them into an Array. I need to put them into an Arraylist so I'm using Arrays.asList(). The problem I'm having is I'm unable to use the size() or length() methods so I cannot make a for loop such as

for (ii = 0; ii < var.length; ii++)

or

for (ii = 0; ii < var.size; ii++)

because I get error: unclassified field java.util.Arrays$ArrayList length

So I tried to use a for each loop, but when I take some action (like ls command for example) in my finally block it only iterates 1 time. But if I just run the command 'echo' it iterates for each element like it's supposed to. Any advice on how to modify my code to get it to iterate for each element in the list when using any command?

Works correctly....

node{
    wrap([$class: 'ConfigFileBuildWrapper', managedFiles: [[fileId: 'dest_hosts.txt', targetLocation: '', variable: 'DEST_HOST']]]) {
        HOST = Arrays.asList(readFile(env.DEST_HOST).split("\\r?\\n"))
        deploy(HOST)
    }
}

@NonCPS
def deploy(host){
    for (String target : host){
        try {
            echo target
        }
        finally {
           echo target
        }
    }
}

OUTPUT (iterates for each element):

[Pipeline] node
Running on <obfuscated>
[Pipeline] {
[Pipeline] wrap
provisoning config files...
copy managed file [<obfuscated>] to file:/var/lib/jenkins/<obfuscated>
[Pipeline] {
[Pipeline] readFile
[Pipeline] echo
www.testhost.com
[Pipeline] echo
www.testhost.com
[Pipeline] echo
www.testhost2.com
[Pipeline] echo
www.testhost2.com
[Pipeline] }
Deleting 1 temporary files
[Pipeline] // wrap
[Pipeline] }
[Pipeline] // node
[Pipeline] End of Pipeline
Finished: SUCCESS

But if I take some action such as 'ls -l' it only iterates 1 time

node{
    wrap([$class: 'ConfigFileBuildWrapper', managedFiles: [[fileId: 'dest_hosts.txt', targetLocation: '', variable: 'DEST_HOST']]]) {
        HOST = Arrays.asList(readFile(env.DEST_HOST).split("\\r?\\n"))
        deploy(HOST)
    }
}

@NonCPS
def deploy(host){
    for (String target : host){
        try {
            echo target
        }
        finally {
           sh 'ls -l'
        }
    }
}

OUTPUT (only iterates 1 time):

[Pipeline] node
Running on <obfuscated>
[Pipeline] {
[Pipeline] wrap
provisoning config files...
copy managed file [<obfuscated>] to file:/var/lib/jenkins/<obfuscated>
[Pipeline] {
[Pipeline] readFile
[Pipeline] echo
www.testhost.com
[Pipeline] sh
[sandbox%2Fpipeline-test-new1] Running shell script
+ ls -l
total 8
-rw-r--r-- 1 jenkins jenkins 10 Jun 17 16:07 someFile
[Pipeline] }
Deleting 1 temporary files
[Pipeline] // wrap
[Pipeline] }
[Pipeline] // node
[Pipeline] End of Pipeline
Finished: SUCCESS

Answer 1

I cannot tell you PRECISELY why, as I've not figured out how to find useful information about Jenkins without spending hours googling, but I can tell you this:

For a moment I thought you can make it run fine by adding 'echo line' AFTER the sh 'echo $line', but that turned out to be caused by Jenkins running a PREVIOUS version of the script...

I tried all sorts of things and none of them worked, then I found this:

Why an each loop in a Jenkinsfile stops at first iteration

Its a known bug in Jenkins pipeline!

(the known bug is JENKINS-26481, which says "At least some closures are executed only once inside of Groovy CPS DSL scripts managed by the workflow plugin")

Answer 2

I prefer this solution:

node('master') {
    stage('Test 1: loop of echo statements') {
        echo_all(abcs)
    }
}

@NonCPS // has to be NonCPS or the build breaks on the call to .each
def echo_all(list) {
    list.each { item ->
        echo "Hello ${item}"
    }
}

If you use a declarative pipeline, you have to wrap the call in a script statement:

stage('master') {
    steps {
        script {
            echo_all(abcs);
        }
    }

Answer 3

ArrayList (and generally Lists) don't have a length or size field, they have a size() method. So use that in the for:

for (ii = 0; ii < var.size(); ii++)

Answer 4

As per this tutorial: https://github.com/jenkinsci/pipeline-plugin/blob/master/TUTORIAL.md#serializing-local-variables

...a method marked with the annotation @NonCPS... will be treated as “native” by the Pipeline engine, and its local variables never saved. However it may not make any calls to Pipeline steps

In your case, the sh call is a pipeline step operation, which you apparently can't perform from within a @NonCPS annotated method.

Regarding turning an array into a List, then since we're in Groovy land you could just use the .toList() method on the array.