Length is not worked in JSON Extractor in Jmeter - json

Question

I need to get the count of card from json file. For this I've used $.storedCards.cards.lenght
in JSON Extractor but it doesn't work. There is an error message:
Options AS_PATH_LIST and ALWAYS_RETURN_LIST are not allowed when using path functions!
After that I've tried JSR223 PostProcessor with next script on goovy
def jsonText = '''${AllCards}''' //${AllCards} has json value
def json = new JsonSlurper().parseText(jsonText)
log.info( "Json length---------->"+json.resource.size())
${CardsCount} = props.get("4") //vars.put(json.resource.size.toString())
but there is problem with set value to my variable. Or when i've created variable in Groovy it was impossible to use outside from script.
My json file
"storedCards":
{
"cards":
[
{
"CardId":"123",
"cardBrand":"Visa",
"lastFourDigits":"2968",
},
{
"CardId":"321",
"cardBrand":"Visa",
"lastFourDigits":"2968",
},
..........
],
How can i get the count of card and set to my Variables? what should i use for this?

Answer 1

Your JSON data seems to be invalid. Assuming you have the valid JSON like below, I'm answering your question.
{
"storedCards": {
"cards": [
{
"CardId": "123",
"cardBrand": "Visa",
"lastFourDigits": "2968"
},
{
"CardId": "321",
"cardBrand": "Visa",
"lastFourDigits": "2968"
}
]
}
}
You dont need to write Groovy code, you can resolve this using JSON Extractor. Instead of using length function, use JSON path predicate like this-
$.storedCards.cards[*]
Though Variable you used in JSON Extractor won't give the solution right away, another JMeter function helps - __RandomFromMultipleVars
Excerpt from documentation -
The RandomFromMultipleVars function returns a random value based on the variable values provided by Source Variables.
The variables can be simple or multi-valued as they can be generated by the following extractors:
Boundary Extractor
Regular Expression Extractor
CSS Selector Extractor
JSON Extractor
XPath Extractor
XPath2 Extractor
Multi-value vars are the ones that are extracted when you set -1 for
Match Numbers. This leads to creation of match number variable called
varName_matchNr and for each value to the creation of variable
varName_n where n = 1, 2, 3 etc.
So once you use the predicate, you will get the count in the yourVariableName_matchNr. Example:-
Hope this help.