Impossibility to iterate over a Map using Groovy within Jenkins Pipeline

Question

We are trying to iterate over a Map, but without any success. We reduced our issue to this minimal example:

def map = [            'monday': 'mon',            'tuesday': 'tue',            ] 

If we try to iterate with:

map.each{ k, v -> println "${k}:${v}" } 

Only the first entry is output: monday:mon

---

The alternatives we know of are not even able to enter the loop:

for (e in map) {     println "key = ${e.key}, value = ${e.value}" } 

or

for (Map.Entry<String, String> e: map.entrySet()) {     println "key = ${e.key}, value = ${e.value}" } 

Are failing, both only showing the exception java.io.NotSerializableException: java.util.LinkedHashMap$Entry. (which could be related to an exception occurring while raising the 'real' exception, preventing us from knowing what happened).

We are using latest stable jenkins (2.19.1) with all plugins up-to-date as of today (2016/10/20).

Is there a solution to iterate over elements in a Map within a Jenkins pipeline Groovy script ?

Answer 1

Its been some time since I played with this, but the best way to iterate through maps (and other containers) was with "classical" for loops, or the "for in". See Bug: Mishandling of binary methods accepting Closure

To your specific problem, most (all?) pipeline DSL commands will add a sequence point, with that I mean its possible to save the state of the pipeline and resume it at a later time. Think of waiting for user input for example, you want to keep this state even through a restart. The result is that every live instance has to be serialized - but the standard Map iterator is unfortunately not serializable. Original Thread

The best solution I can come up with is defining a Function to convert a Map into a list of serializable MapEntries. The function is not using any pipeline steps, so nothing has to be serializable within it.

@NonCPS def mapToList(depmap) {     def dlist = []     for (def entry2 in depmap) {         dlist.add(new java.util.AbstractMap.SimpleImmutableEntry(entry2.key, entry2.value))     }     dlist } 

This has to be obviously called for each map you want to iterate, but the upside it, that the body of the loop stays the same.

for (def e in mapToList(map)) {     println "key = ${e.key}, value = ${e.value}" } 

You will have to approve the SimpleImmutableEntry constructor the first time, or quite possibly you could work around that by placing the mapToList function in the workflow library.