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Editorial Team
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Asked: 2026-05-25T20:56:55+00:00

I was writing code and I noticed some odd behavior in Groovy when I

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I was writing code and I noticed some odd behavior in Groovy when I am dealing with XML and Maps. I thought about it and can’t figure out why is it happening and should it that way.

I wrote sample code with 3 examples. Crucial difference between map1 & map3 is only on the following part:

Map1: 

map1 << ["${it.name()}":it.value()]

Map3: 

map3["${it.name()}"]=it.value()

Here is full code, you can copy-paste it into Groovy console:

def xml = '<xml><head>headHere</head><body>bodyHere</body></xml>'


Map map1 = [:]

def node = new XmlParser().parseText(xml) 

node.each {
      map1 << ["${it.name()}": it.value()]
} 

println map1
println map1["head"]

println ">>>>>>>>>>>>>>>>>>>>>>"



Map map2 = [:]

map2 << ["head":"headHere"]
map2 << ["body":"bodyHere"]

println map2
println map2["head"]

println "<<<<<<<<<<<<<<<<<<<<<<"



def xml2 = '<xml><head>headHere</head><body>bodyHere</body></xml>'    

Map map3 = [:]

def node2 = new XmlParser().parseText(xml2) 

node2.each {
      map3["${it.name()}"]=it.value()
} 

println map3
println map3["head"]

The result that I am getting is following:

[head:[headHere], body:[bodyHere]]
null

[head:headHere, body:bodyHere]
headHere

[head:[headHere], body:[bodyHere]]
[headHere]

Even thou map1 and map3 look the same, the result of map[“head”] is totally different, first gives null and second gives the actual result. I don’t understand why is it happening. I spent some time on it and still don’t get it. I used .getProperty() to get info on a class, but it looks the same and feels the same on both maps and object inside. I tried couple more things and nothing gives me any idea on what is happening. I even tried different OS (Win XP, Mac OS) and still nothing.

I don’t have any ideas anymore, please can one some explain odd behavior, why is it happening and what is the difference between map << [key:object] and map[key] = object?

Thank you.

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1 Answer

  1. Editorial Team

    One thing that might help is, don’t use GStrings for your keys. Groovy supports using objects directly as keys by wrapping them in parentheses.

    From the manual:

    Map keys are strings by default: [a:1] is equivalent to [“a”:1]. But if you really want a variable to become the key, you have to wrap it between parentheses: [(a):1].

    Fully working example:

    def xml = '<xml><head>headHere</head><body>bodyHere</body></xml>'

Map map1 = [:]
def node = new XmlParser().parseText(xml)
node.each {
    map1 << [ (it.name()): it.value() ]
}

println map1
println map1["head"]
println ">>>>>>>>>>>>>>>>>>>>>>"

Map map2 = [:]

map2 << ["head":"headHere"]
map2 << ["body":"bodyHere"]

println map2
println map2["head"]

println "<<<<<<<<<<<<<<<<<<<<<<"

def xml2 = '<xml><head>headHere</head><body>bodyHere</body></xml>'

Map map3 = [:]

def node2 = new XmlParser().parseText(xml2)

node2.each {
    map3[it.name()] = it.value()
}

println map3
println map3["head"]

    The output is:

    [head:[headHere], body:[bodyHere]]
[headHere]
>>>>>>>>>>>>>>>>>>>>>>
[head:headHere, body:bodyHere]
headHere
<<<<<<<<<<<<<<<<<<<<<<
[head:[headHere], body:[bodyHere]]
[headHere]
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