Groovy: Manipulate variable from within each - groovy

Question

I'd like to manipulate a variable in Groovy from within the closure of each, like this:
def stringTest = ''
def foo = ['one', 'two', 'three']
foo.each {
stringTest.concat(it)
}
println stringTest
But this gives me the following error:
| Error 2013-03-13 15:26:12,330 [http-bio-8080-exec-2] ERROR
errors.GrailsExceptionResolver - NoSuchMethodError occurred when
processing request: [GET] /Reporting-Web/reporting/show/1
reporting.web.AppFiguresService$_getProductIDs_closure2.(Ljava/lang/Object;Ljava/lang/Object;Lgroovy/lang/Reference;)V.
Stacktrace follows: Message: Executing action [show] of controller
[com.xyz.reporting.ReportingController] caused exception: Runtime
error executing action Line | Method
->> 195 | doFilter in grails.plugin.cache.web.filter.PageFragmentCachingFilter
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - | 63 | doFilter in grails.plugin.cache.web.filter.AbstractFilter | 895 | runTask in java.util.concurrent.ThreadPoolExecutor$Worker |
918 | run in '' ^ 680 | run . . in java.lang.Thread
Caused by ControllerExecutionException: Runtime error executing action
->> 195 | doFilter in grails.plugin.cache.web.filter.PageFragmentCachingFilter
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - | 63 | doFilter in grails.plugin.cache.web.filter.AbstractFilter | 895 | runTask in java.util.concurrent.ThreadPoolExecutor$Worker |
918 | run in '' ^ 680 | run . . in java.lang.Thread
Caused by InvocationTargetException: null
->> 195 | doFilter in grails.plugin.cache.web.filter.PageFragmentCachingFilter
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - | 63 | doFilter in grails.plugin.cache.web.filter.AbstractFilter | 895 | runTask in java.util.concurrent.ThreadPoolExecutor$Worker |
918 | run in '' ^ 680 | run . . in java.lang.Thread
Caused by NoSuchMethodError:
reporting.web.Foo$_getProductIDs_closure2.(Ljava/lang/Object;Ljava/lang/Object;Lgroovy/lang/Reference;)V
->> 77 | getProductIDs in reporting.web.Foo$$ENzya8Hg
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - | 45 | show in com.xyz.reporting.Foo | 195 | doFilter in grails.plugin.cache.web.filter.PageFragmentCachingFilter | 63 |
doFilter in grails.plugin.cache.web.filter.AbstractFilter | 895 |
runTask in java.util.concurrent.ThreadPoolExecutor$Worker | 918 |
run in '' ^ 680 | run . . in java.lang.Thread
I'm quite new to Groovy, any help would be great here!

Answer 1

This works...
def stringTest = ''
def foo = ['one', 'two', 'three']
foo.each {
stringTest += it
}
println stringTest

Answer 2

the function "concat()" returns a string:
stringTest = stringTest.concat(it)
To modify the iterator in the closure is not possible.
//Edit
The error msg is a grails error, while the controller can not open the function "show()"

Answer 3

Java strings are immutable. You can collect the concatened string:
def stringTest = ''
def foo = ['one', 'two', 'three']
stringTest = foo.collect { stringTest + it }.join()
assert stringTest == "onetwothree"