Grails 2.x added a new method in params object “list”. This method is used in case you are not sure weather you got a string(single request parameters of a name) or a list(multiple request parameters of the same name) in params. This method always return a list. This method convert string params to list.

syntax

params.list('parameter_name')

eg. if request is

../controller/action?testData=A&testData=B

then

params.list('testData')

gives

['A', 'B']

and if request is

../controller/action?testData=A

then

params.list('testData')

gives

['A']

and if request is

../controller/action

then

params.list('testData')

gives a empty list []