/**
  * Return the request parameters as a Properties. Only the first value of multivalued parameters
  * is included.
  */
 Properties getParamsAsProps() {
   Properties props = new Properties();
   for (Enumeration en = req.getParameterNames(); en.hasMoreElements(); ) {
     String name = (String) en.nextElement();
     props.setProperty(name, req.getParameter(name));
   }
   return props;
 }
 /** Concatenate params for URL string */
 String concatParams(Properties props) {
   if (props == null) {
     return null;
   }
   java.util.List list = new ArrayList();
   for (Iterator iter = props.keySet().iterator(); iter.hasNext(); ) {
     String key = (String) iter.next();
     String val = props.getProperty(key);
     if (!StringUtil.isNullString(val)) {
       list.add(key + "=" + urlEncode(val));
     }
   }
   return StringUtil.separatedString(list, "&");
 }
 String modifyParams(String key, String val) {
   Properties props = getParamsAsProps();
   props.setProperty(key, val);
   return concatParams(props);
 }