会话中的问题

request.setCharacterEncoding("gb2312");
response.setContentType("text/html;charset=GBK");
PrintWriter out = response.getWriter();
String url=request.getHeader("referer");
if(url.indexOf("?")!=-1)
{
url=url.substring(0,url.indexOf("?"));
}
String test=request.getParameter("test");
String url1=response.encodeUrl(url+"?test="+test);
String url2=response.encodeRedirectUrl(url1);
response.sendRedirect(url2);
out.flush();
out.close();中这句是什么意思if(url.indexOf("?")!=-1)
{
url=url.substring(0,url.indexOf("?"));
}和String url1=response.encodeUrl(url+"?test="+test);