Closure in grails controller not picking up arguments - grails

Question

I'm trying to consolidate redundant code in my controller using a utility closure to do generic exception handler and response generation.
For instance, I want to consolidate this:
def newUser(){
def model = [:]
def errors
try{
model += [newUserObj:dao.newUser(...)]
}catch(Exception e){
errors = e.getMessage()
}
renderJson(model,error)
}
..to this:
def newUser(){
def model = [:]
def errors
doRequest(model, errors){ ->
model += [newUserObj:dao.newUser(...)]
}
}
..while moving boilerplate code to a closure:
def doRequest(model, errors, clsr){
try{
clsr.call()
}catch(Exception e){
errors = e.getMessage()
}
//!! model here is null !!
renderJson(model,error)
}
The problem happens in doRequest() when renderJson() is invoked; model is null, even though I confirmed it's assigned correctly inside the closure at model += [newUserObj:dao.newUser(...)].
Workaround
I managed to get around this issue by just returning the model from the closure:
def newUser(){
doRequest(){ ->
def model = [:]
def errors
model += [newUserObj:dao.newUser(...)]
[model:model, errors:errors]
}
}
def doRequest(clsr){
def model = [:]
def errors
try{
def r = clsr.call()
model = r['model']
errors = r['errors']
}catch(Exception e){
errors = e.getMessage()
}
renderJson(model,error)
}
..but this doesn't seem Groovy at all, I'm creating boiler plate code I was trying to avoid in the first place.

Answer 1

Is this what you were looking for?
import grails.converters.JSON
//Closure implementation
def doRequest(Closure clsr) {
def model = [:]
def errors = /No Error Message Yet/
try {
model = clsr(model)
} catch(Exception e) {
errors = e.getMessage()
}
renderJson(model, errors)
}
//Mimics an action method
def newUser() {
doRequest { model ->
model += [a:1] //Mimics the call to DAO in your question
//make sure to return the model after all operations completed
//model
}
}
//Mimics the render to JSON utility
private JSON renderJson(model, error) {
[model: model, errors: error] as JSON
}
//Mimics call to the action method
assert newUser().toString() ==
/{"model":{"a":1},"errors":"No Error Message Yet"}/
I could have implemented doRequest() something as below, but I did not because in that case model and errors would become part of the class (in your case it will be Controller's global properties) which we do not want.
def doRequest(Closure clsr) {
try {
clsr.resolveStrategy = Closure.DELEGATE_FIRST
clsr.delegate = this
clsr()
} catch(Exception e) {
errors = e.getMessage()
}
renderJson(model, errors)
}