* 将map对象参数转换成String=String&方式

    * @param params

    * @param charset

    * @return

    * @throws UnsupportedEncodingException

    */

   public static String generateParams(Map<String, String> params,String charset) throws UnsupportedEncodingException{

      int flag=0;

      StringBuffer ret=new StringBuffer();

      Iterator iter = params.entrySet().iterator();

      while (iter.hasNext()) {

          Map.Entry entry = (Map.Entry) iter.next();

          Object key = entry.getKey();

          Object val = entry.getValue();

          if(val!=null){

          if(flag==0){

            ret.append(key);

            ret.append("=");

            if(charset!=null&&!charset.equals("")){

            ret.append(URLEncoder.encode(val.toString(), charset));

            }else{

               ret.append(val.toString());

            }

            flag++;

          }else{

            ret.append("&");

            ret.append(key);

            ret.append("=");

            if(charset!=null&&!charset.equals("")){

              ret.append(URLEncoder.encode(val.toString(), charset));

              }else{

                 ret.append(val.toString());

              }

          }

          }

      }

      return ret.toString();

   }