Rest API call encoding in Flutter and decoding in Java

Question

My Flutter app calls a REST API method /user/search/<search string> and I am forming the URL endpoint using encodeQueryComponent like this:

String endpoint = "/user/search/"+Uri.encodeQueryComponent(searchString);

The back-end implemented in Java tries to retrieve the search string like this:

String value = URLDecoder.decode(value, StandardCharsets.UTF_8.toString());

However, when the search string contains the + sign, the raw encode string in the back-end contains %2B and the decoded String contains space. As a temporary hack, I am currently doing value = value.replace("%2B", "+"); instead of decode. But this is obviously not the right approach because the search string may contain characters from any language or special characters.

Can someone tell me what is the right way to get the original string sent by the user in Java?