How to access a variable outside of a loop in Groovy - groovy

Question

Beginner alert! I have a simple Groovy script that aims to break an argument list into key-value pairs, stored in an associative array (HashMap?). The code works fine until the point where it splits the parameters, but when it tries to put the results back into the array, it throws an exception, stating it cannot access a null element.
I suppose the reason for this is that it can't access the variable that was declared outside the loop.
Here's the script:
def input = "https://weyland-yutani.corp/engineering/bio?param1=1&param2=2"
def params = [:] // wanna store key-value pairs here
if (input.split('\\?').size() >= 2) {
def p = input.split('\\?').last() // get the param string
p.split('\\&').each { // cut the string into an argument list
def keyval = it.split('=') // cut the argument into a key-value pair
println keyval // <-- prints "[param1, 1]", looks okay
params[keyval[0]].put(keyval[1]) // ERROR: "Cannot invoke method put() on null object"
//params[keyval[0]].add(keyval[1]) // ERROR, same sh**
}
}
Error message:
Caught: java.lang.NullPointerException: Cannot invoke method put() on null object
java.lang.NullPointerException: Cannot invoke method put() on null object
at jdoodle$_run_closure1.doCall(jdoodle.groovy:10)
[...]
As it was stated in this article, the way you declare a variable can affect it's scope, but none of my tries succeeded.
Could you give me an advice what am I missing?

Answer 1

The following code:
def input = "https://weyland-yutani.corp/engineering/bio?param1=1&param2=2"
def params = input.tokenize('?').last().tokenize('&').collectEntries { keyval ->
keyval.tokenize('=')
}
println params.getClass()
println params
demonstrates one way of doing this. When run, this prints:
─➤ groovy solution.groovy
class java.util.LinkedHashMap
[param1:1, param2:2]
─➤
As an alternative, if you are ok with using an external library, you could use a url parsing class. This example from HttpBuilder (which is a tad outdated at this point, there are probably others out there):
#Grab('org.codehaus.groovy.modules.http-builder:http-builder:0.7.2')
import groovyx.net.http.URIBuilder
def input = "https://weyland-yutani.corp/engineering/bio?param1=1&param2=2"
def uri = new URIBuilder(input)
println uri.query.getClass()
println uri.query
which, when run, prints:
─➤ groovy solution2.groovy
class java.util.HashMap
[param1:1, param2:2]
─➤
As another example, this time using google http client library class GenericUrl:
#Grab('com.google.http-client:google-http-client:1.39.1')
import com.google.api.client.http.GenericUrl
def input = "https://weyland-yutani.corp/engineering/bio?param1=1&param2=2"
def url = new GenericUrl(input)
println (url instanceof Map)
url.each { k, v ->
println "$k -> $v"
}
println "value of param1: ${url.param1}"
which, when executed prints:
─➤ groovy solution3.groovy
true
param1 -> [1]
param2 -> [2]
value of param1: [1]
─➤
It should be noted that google does the right thing here. When asking for the value of a parameter, the answer should really be a list. This is because you can say ?a=1&a=2&a=3 which from what I understand should be interpreted not as replacing the value of a, but rather as a being a list of values 1, 2, 3.
So when you ask the google library for the value of a param, you get back a list which in this case happens to be one param long.

Answer 2

There is no code that is ever putting anything in params so when you do params[keyval[0]] that will always evaluate to null, so params[keyval[0]].put(keyval[1]) can't work because you are invoking .put on a null reference.