groovy json builder json.call - to combine single Json output

Question

I have two ArrayList and I need to print in JSON format. I used the below code to print the ArrayList as JSON string

def a = ['R1','R2']
def b = ['R3','R4']
def json = new groovy.json.JsonBuilder()

json set1: a
println groovy.json.JsonOutput.prettyPrint(json.toString())

json set2: b
println groovy.json.JsonOutput.prettyPrint(json.toString())

Actual output

{
    "set1": [
        "R1",
        "R2"
    ]
}

{
    "set2": [
        "R3",
        "R4"
    ]
}

It will be printed as two JSON files, but do I need to print/combine all two sets into a single JSON output?

My expected Output

{
  "set1": [
    "R1",
    "R2"
  ],
  "set2": [
    "R3",
    "R4"
  ]
}

Answer 1

def a=[111,222,333]
def b=[444,555,666]

def jb = new groovy.json.JsonBuilder() 
jb {
  set1(a)
  set2(b)
}
println jb.toPrettyString()

Or

println new groovy.json.JsonBuilder([ set1:a, set2:b ]).toPrettyString()