$.ajax(
url: "hoge",
data: { str: "文字列"},
...
response.setContentType("text/html;charset=MS932");
PrintWriter out = response.getWriter();
String str = Utility.getServletParameter(request, "str");
out.print("渡された文字列: " + str);
response.setContentType("text/html;charset=UTF-8");