由于您使用Groovy标记了问题，其本机JsonBuilder似乎可以正常工作:

Since you tagged the question with Groovy, its native JsonBuilder seems to work as expected:

import groovy.json.*

a = new JsonBuilder(mything: "[1, 2, 3]")

assert a.toString() == '{"mything":"[1, 2, 3]"}'

b = new JsonBuilder(params: a.getContent())

assert b.toString() == '{"params":{"mything":"[1, 2, 3]"}}'