使用ajax处理中文乱码

JSP页面中
　　ajax.open("post","${pageContext.request.contextPath}/manage/UserCheckServlet?user="+encodeURI(eu_user_id.value)+"&t="+Math.random());
Servlet中
　　String user = req.getParameter("user");
　　user = new String(user.getBytes("ISO8859-1"),"UTF-8");