import groovy.json.JsonSlurper
def response = messageExchange.response.responseContent
log.info "response : "+ response
def slurper = new JsonSlurper()
def json = slurper.parseText response
log.info "json : "+ json
log.info "json size : "+json.size()
assert json.SecId.size() == 6
log.info "The first json : "+json[0]
log.info "The first SecId : "+json[0].SecId
assert json[0].SecId =="0P0000187J"
JsonSlurper (groovy 2.4.3 API) : http://docs.groovy-lang.org/latest/html/gapi/groovy/json/JsonSlurper.html