How to extract from html source code

[newcoder1010]

Hello,

HTML source code:

https://www.walmart.com/ip/Parent-s-Choice-Diapers-Size-3-36-Diapers/14912811

If you view html source code, you will see the upc code. 

"standardusItemId":"401199665","upc":"681131167444","fetched":true,

 

I like to write a program to just print the code(value only).

 

 String str = driver.getPageSource();
            System.out.println("-----");

            System.out.println(str);
            System.out.println("field" + str.indexOf("upc"));
            
            System.out.println("value" + str.indexOf("681131167444"));

Result:

index1033185
upc603459

I know code is not complete. My code gets the page source just fine. Only extracting the code is not working. Please advise!