When you want to query a REST API but have values that need url-encoding first, you can use a User Defined Java Expression:

In this particular example it is necessary as PDI would throw the error (“Illegal character in path”) if you query the following URL unmodified from a string:

https://api.crossref.org/works/10.1671/0272-4634(2007)27%5B827:TFSFHH%5D2.0.CO;2