Jenkins Shared Library Global/Singleton Class - jenkins

Question

I am looking for some guidance on the design of a Jenkins Shared Library, with respect to using a class, initializing it, and then being able to use that instance in any of my vars files.
Structure
src
- foo
- class
- Configuration.groovy
vars
- cicd.groovy
- doMore.groovy
Class
The following is a class I would like to initialize once, but then use anywhere, without having to pass it into each vars function, or reinitialize every time.
package foo.class
public class Configuration {
public String Foo
public String Bar
}
Vars
In my cicd.groovy vars file, I have something like this:
#!groovy
import foo.class.Configuration
def call () {
return initCicd()
}
def initCicd() {
configuration = new Configuration()
configuration.Foo = 'FOO'
return configuration
}
But, in other vars files like doMore.groovy, I would like to use the same configuration instance.
#!groovy
import foo.class.Configuration
def call () {
println configuration.Foo
}
Is there a Singleton pattern that that works in Jenkins Shared Library, or a way to reference an instance across vars files or steps? If possible, please share an example.
Thanks!

Answer 1

You can simply use Groovy's #Singleton annotation for your Configuration class and use Configuration.instance wherever you want to access configuration settings. Consider following example:
.
├── src
│   └── foo
│   └── Configuration.groovy
└── vars
├── cicd.groovy
└── doMore.groovy
src/foo/Configuration.groovy
package foo
#Singleton
class Configuration {
public String foo = 'foo_123'
public String bar = 'bar_456'
}
vars/cicd.groovy
#!groovy
import foo.Configuration
def call() {
return initCicd()
}
def initCicd() {
println Configuration.instance.foo
return Configuration.instance
}
vars/doMore.groovy
#!groovy
import foo.Configuration
def call() {
println Configuration.instance.bar
}
In the pipeline script I simply call:
cicd()
doMore()
And I get something like that in the console log:
Loading library default_jenkins_libs#master
Attempting to resolve master from remote references...
> git --version # timeout=10
> git ls-remote -h -t file:///var/jenkins_home/libraries # timeout=10
Found match: refs/heads/master revision 4fa988ccde542d77d19febd72f532ef996971a5d
> git rev-parse --is-inside-work-tree # timeout=10
Fetching changes from the remote Git repository
> git config remote.origin.url file:///var/jenkins_home/libraries # timeout=10
Fetching without tags
Fetching upstream changes from file:///var/jenkins_home/libraries
> git --version # timeout=10
> git fetch --no-tags --progress file:///var/jenkins_home/libraries +refs/heads/*:refs/remotes/origin/*
Checking out Revision 4fa988ccde542d77d19febd72f532ef996971a5d (master)
> git config core.sparsecheckout # timeout=10
> git checkout -f 4fa988ccde542d77d19febd72f532ef996971a5d
Commit message: "update"
> git rev-list --no-walk 39890b4ca39bf32ebde8c7ad143b110bf16cf6b3 # timeout=10
[Pipeline] echo
foo_123
[Pipeline] echo
bar_456
[Pipeline] End of Pipeline
Finished: SUCCESS
The one downside of using singletons is that they can get modified anywhere and this change is populated to all callers.