[JENKINS-54982] Using Java8 Streams evaluates whole expression to Boolean

I'm trying to write a common library building Docker images from Dockerfile. I wrote a reusable global pipeline, where I'm iterating over Dockerfile lines. I tried to use Java 8 Streams, however I ended up with issue potentially related to JENKINS-26307 and JENKINS-42769, which is not related not to Groovy functional features, but Java 8 feature.

 An example code used:

def getMissingLabels(Map<String, String> labels) {

 ['label1', 'label2', 'label3', 'label4'].stream()

.filter({ label -> !isLabelDefined(label, labels) })

.collect(Collectors.toList())

}

Whole stream execution results in "false" boolean result, instead of a list. Even complex streams are passing through, but evaluates to "false". When using more complex stream like:

 

Arrays.stream(splitted)

    .filter { it.startsWith('LABEL') }

    .map { it.replaceAll('(LABEL)|"', '') }

    .map { it.trim() }

    .map { it.split('=', 2) }

    .collect(Collectors.toMap(

    { val -> val[0].toLowerCase() },

    { val -> val[1] }))

it enters only first filter expression and does not evaluate the rest.

When replaced functional style code with typical imperative style (for loop) it works.

 

---
Originally reported by filipowm, imported from: Using Java8 Streams evaluates whole expression to Boolean

• status: Open
  
• priority: Minor
  
• component(s): workflow-cps-plugin
  
• label(s): pipeline, pipeline-triaged
  
• resolution: Unresolved
  
• votes: 3
  
• watchers: 5
  
• imported: 2025-12-07
  

Raw content of original issue

I'm trying to write a common library building Docker images from Dockerfile. I wrote a reusable global pipeline, where I'm iterating over Dockerfile lines. I tried to use Java 8 Streams, however I ended up with issue potentially related to JENKINS-26307 and JENKINS-42769, which is not related not to Groovy functional features, but Java 8 feature.


 An example code used:



def getMissingLabels(Map<String, String> labels) {

 ['label1', 'label2', 'label3', 'label4'].stream()

        .filter({ label -> !isLabelDefined(label, labels) })

        .collect(Collectors.toList())

}





Whole stream execution results in "false" boolean result, instead of a list. Even complex streams are passing through, but evaluates to "false". When using more complex stream like:


 



Arrays.stream(splitted)

            .filter { it.startsWith('LABEL') }

            .map { it.replaceAll('(LABEL)|"', '') }

            .map { it.trim() }

            .map { it.split('=', 2) }

            .collect(Collectors.toMap(

            { val -> val[0].toLowerCase() },

            { val -> val[1] }))





it enters only first filter expression and does not evaluate the rest.


When replaced functional style code with typical imperative style (for loop) it works.


 

• environment: Jenkins 2.153, Pipeline 2.6

Start by reproducing the two Java 8 Stream examples in the workflow-cps-plugin context described, using the reported Jenkins 2.153 and Pipeline 2.6 environment if available. Trace how the first filter and the later collect operation are handled; done means the examples return their expected list or map and execute every stream stage, with regression coverage.

Written by the indexing model from the issue text.