%40 is a URL encoded @ character. Java has some helper classes to do this encode and decode URL characters.
To URL encode, use the following:
var originalQueryString = "email=support@qvera.com";
var encodedQueryString = java.net.URLEncoder.encode(originalQueryString, "UTF-8");
The above results in "email=support%40qvera.com"
To URL decode use the following:
var encodedQueryString = "email=support%40qvera.com";
var decodedQueryString = java.net.URLDecoder.decode(encodedQueryString, "UTF-8");
The above results in "email=support@qvera.com"
Here is a reference for other URL encoding characters.