how to execute a GET request in JIRA behavior scripts based on the customfield value?

[rakesh rocckz]

I have two custom fields "URL" and a multiline textbox. whenever someone pasted a URL in URL custom field in the background it should run the GET request and get the response in JSON format and it should show that JSON response in the other multiline text field. is it possible through Behavior scripts? please help me out how to execute a GET request as soon as someone pastes a URL in the URL field in Jira issue it should a GET execute for that URL and should show the response in the multiline-text field. 

[PD Sheehan]

See my comment on your discussion post: https://community.atlassian.com/t5/Jira-discussions/how-to-execute-a-URL-in-url-customfield-in-behavior-script-and/td-p/1157749#U1158992