code: public static String getSolrAddDocument(Map<String, String> values) {
      StringBuilder builder = new StringBuilder();
      builder.append("<add><doc>");
      for (Map.Entry<String, String> pair : values.entrySet()) {
        XMLUtils.addSolrField(builder, pair);
      }
      builder.append("</doc></add>");
      return builder.toString();
    }
docs: Returns Apache Solr add command.
  
  @param values
  values to include
  @return XML as String