code: public String getEncodeType() {
          String contentType = header.get("Content-Type");
          if (null != contentType) {
              for (String tmp : contentType.split(";")) {
                  if (tmp == null)
                      continue;
                  tmp = tmp.trim();
                  if (tmp.startsWith("charset=")) {
                      tmp = Strings.trim(tmp.substring(8)).trim();
                      if (tmp.contains(","))
                          tmp = tmp.substring(0, tmp.indexOf(',')).trim();
                      return tmp;
                  }
              }
          }
          return Encoding.UTF8;
      }
docs: 根据Http头的Content-Type获取网页的编码类型，如果没有设的话则返回null