code: public String generate() throws OAuthMessageSignerException {
  
          try {
              String normalizedUrl = normalizeRequestUrl();
              String normalizedParams = normalizeRequestParameters();
  
              return request.getMethod() + '&' + OAuth.percentEncode(normalizedUrl) + '&'
                      + OAuth.percentEncode(normalizedParams);
          } catch (Exception e) {
              throw new OAuthMessageSignerException(e);
          }
      }
docs: Builds the signature base string from the data this instance was
  configured with.
  
  @return the signature base string
  @throws OAuthMessageSignerException