How to pass HttpServletRequest JSON inbound data from controller to service method

I understand the general dictum to isolate business logic to service methods in Grails. All my previous Grails web services, have no inbound JSON, XML etc. Currently, I am required to take JSON payload, which contains {finish_time: 2020-05-12T18:19:00Z, start_time: 2020-05-14T18:19:00Z}, to use in my SQL. Running Grails 2.5.6. Unfortunately, I have no idea how service methods, can access the inbound JSON payload data. This has to be common, but I am not understanding data pass/access from controller to service methods. I’m not versed in Grails well enough to waste ya’lls time showing what I’ve tried. I have not found any examples/explanations of service methods working on inbound https posted JSON/XML data from the controller. Thank You in advance, as to me this seems like a very fundamental task.

Solution

Pass the json data as an argument to a service method that handles this operation

Controller action

def actionName() {
    def json = '{"finish_time": "2020-05-12T18:19:00Z", "start_time": "2020-05-14T18:19:00Z"}'
    serviceInstance.methodName(json)
}

Service method

def methodName(json) {
    def jsonSlurper = new JsonSlurper()
    def data = jsonSlurper.parseText(json) // here data is a Groovy data structures in this case a Map

    // ... sql logic
}