code: public void printHead(final Writer writer) throws IOException {
          final String eol = "\r\n";
          int pos = 0;
          try {
              for (final String line : this.head()) {
                  if (pos == 0 && !RsPrint.FIRST.matcher(line).matches()) {
                      throw new IllegalArgumentException(
                          String.format(
                              // @checkstyle LineLength (1 line)
                              "first line of HTTP response \"%s\" doesn't match \"%s\" regular expression, but it should, according to RFC 7230",
                              line, RsPrint.FIRST
                          )
                      );
                  }
                  if (pos > 0 && !RsPrint.OTHERS.matcher(line).matches()) {
                      throw new IllegalArgumentException(
                          String.format(
                              // @checkstyle LineLength (1 line)
                              "header line #%d of HTTP response \"%s\" doesn't match \"%s\" regular expression, but it should, according to RFC 7230",
                              pos + 1, line, RsPrint.OTHERS
                          )
                      );
                  }
                  writer.append(line);
                  writer.append(eol);
                  ++pos;
              }
              writer.append(eol);
          } finally {
              writer.flush();
          }
      }
docs: Print it into a writer.
  @param writer Writer to print into
  @throws IOException If fails
  @since 2.0