HttpServletRequest UTF-8 Encoding

Paul's suggestion seems like the best course of action, but if you're going to work around it, you don't need URLEncoder or URLDecoder at all:

String item = request.getParameter("param"); 

byte[] bytes = item.getBytes(StandardCharsets.ISO_8859_1);
item = new String(bytes, StandardCharsets.UTF_8);

// Java 6:
// byte[] bytes = item.getBytes("ISO-8859-1");
// item = new String(bytes, "UTF-8");

Update: Since this is getting a lot of votes, I want to stress BalusC's point that this definitely is not a solution; it is a workaround at best. People should not be doing this.

I don't know exactly what caused the original issue, but I suspect the URL was already UTF-8 encoded, and then was UTF-8 encoded again.

Well, I found a way to resolve my problem, I guess that's not the better solution, but it does works..

  String item = request.getParameterValues("param"); // Hélène
  item = URLEncoder.encode( model.getNameItem(), "ISO-8859-1" ); // H%C3%A9l%C3%A8ne
  item = URLDecoder.decode( item, "UTF-8" ); // and finally : Hélène

If it can help anyone else, I'm glad to help :)

PS : Paul, I didn't answer you earlier but I already did those things. Thanks anyway for your help.

If you are using Apache Tomcat, request.setCharacterEncoding("UTF-8") only works with POST request.

For GET request, you need add URIEncoding="UTF-8" on your <Connector> in server.xml.

See more in FAQ/CharacterEncoding - Apache Tomcat wiki space.