Java code to avoid identical answers and custom validation for URL links

Hello, I am creating a survey where I ask participants to search online for some unique URL image links and to enter them in 200 text entry question. I would like to set up a java code that helps me to avoid identical text entries (i.e., subjects can copy paste the same links for many times). I could set up custom validation on each of the questions that it will only pass if what they enter is not equal to the text entry value for any of the previous questions( by using a piped text) but I was wondering whether there is a java code for this? Second, the text entry must contain "https://" or something like that so that it has to be a link. Is it possible to do it with a java code? If I use a regex how should the expression look like? Many thanks!!