public HttpRequest contentType(final String contentType, final String charset) {
    if (charset != null && charset.length() > 0) {
      final String separator = "; " + PARAM_CHARSET + '=';
      return header(HEADER_CONTENT_TYPE, contentType + separator + charset);
    } else
      return header(HEADER_CONTENT_TYPE, contentType);
  }
Set the 'Content-Type' request header to the given value and charset

@param contentType
@param charset
@return this request
lib/src/main/java/com/github/kevinsawicki/http/HttpRequest.java