looping a template using groovy GStringTemplateEngine() - groovy

Question

My requirement is to create a template engine to support a looping in it.
The final template should look something like this:
#cat output.template
env:
- name : param1
value : 1
- name : param2
value : 2
I have pseudo code to explain my requirement
def f = new File('output.template')
def engine = new groovy.text.GStringTemplateEngine()
def mapping = [
[ name : "param1",
value : "1"],
[ name : "param2",
value : "2" ]
] // This mapping can consists of a multiple key value pairs.
def Template = engine.createTemplate(f).make(mapping)
println "${Template}"
Can someone help me how to achieve this requirement of looping inside the templates and how should I modify my template?
*UPDATE : All the solutions provided by tim_yates or by Eduardo Melzer has resulted in following output with extra blank lines at the end of template. What could be the reason for that?* Are the solution providers not able to see this behavior or the issue is my system only?.
# groovy loop_template.groovy
env:
- name: param1
value : 1
- name: param2
value : 2
root#instance-1:

Answer 1

Change your template file to look like this:
#cat output.template
env:<% mapping.eachWithIndex { v, i -> %>
- name : ${v.name}
value : ${v.value}<% } %>
As you can see, your template file expects an input parameter called mapping, so you need change your main code to something like this:
def f = new File('output.template')
def engine = new groovy.text.GStringTemplateEngine()
def mapping = [
[ name : "param1", value : "1"],
[ name : "param2", value : "2"]
] // This mapping can consists of a multiple key value pairs.
def Template = engine.createTemplate(f).make([mapping: mapping])
println "${Template}"
Output:
#cat output.template
env:
- name : param1
value : 1
- name : param2
value : 2