如何更改客户端地址？

[source lang="java"]
String url=request.getRequestURI();
if(request.getQueryString()!=null)
url+="?"+request.getQueryString();
String fid=request.getParameter("fid");
if(fid==null)
{
fid=""+request.hashCode();
response.sendRedirect(url+"?fid="+fid);
}
[/source]