FCS 2.0 Endpoint Developer’s Tutorial

if (request.isQueryType(Constants.FCS_QUERY_TYPE_FCS)) {
    /*
     * Got a FCS query (SRU 2.0).
     * Translate to a proper Lucene query
     */
    final FCSQueryParser.FCSQuery q = request.getQuery(FCSQueryParser.FCSQuery.class);
    query = makeSpanQueryFromFCS(q);
}

private SpanQuery makeSpanQueryFromFCS(FCSQueryParser.FCSQuery query) throws SRUException {
    QueryNode tree = query.getParsedQuery();
    logger.debug("FCS-Query: {}", tree.toString());
    // crude query translator
    if (tree instanceof QuerySegment) {
        QuerySegment segment = (QuerySegment) tree;
        if ((segment.getMinOccurs() == 1) && (segment.getMaxOccurs() == 1)) {
            QueryNode child = segment.getExpression();
            if (child instanceof Expression) {
                Expression expression = (Expression) child;
                if (expression.getLayerIdentifier().equals("text") &&
                        (expression.getLayerQualifier() == null) &&
                        (expression.getOperator() == Operator.EQUALS) &&
                        (expression.getRegexFlags() == null)) {
                    return new SpanTermQuery(new Term("text", expression.getRegexValue().toLowerCase()));
                } else {
                    throw new SRUException(
                            Constants.FCS_DIAGNOSTIC_GENERAL_QUERY_TOO_COMPLEX_CANNOT_PERFORM_QUERY,
                            "Endpoint only supports 'text' layer, the '=' operator and no regex flags");
                }
            } else {
                throw new SRUException(
                        Constants.FCS_DIAGNOSTIC_GENERAL_QUERY_TOO_COMPLEX_CANNOT_PERFORM_QUERY,
                        "Endpoint only supports simple expressions");
            }
        } else {
            throw new SRUException(
                    Constants.FCS_DIAGNOSTIC_GENERAL_QUERY_TOO_COMPLEX_CANNOT_PERFORM_QUERY,
                    "Endpoint only supports default occurances in segments");
        }
    } else {
        throw new SRUException(
                Constants.FCS_DIAGNOSTIC_GENERAL_QUERY_TOO_COMPLEX_CANNOT_PERFORM_QUERY,
                "Endpoint only supports single segment queries");
    }
}

@Override
public void writeRecord(XMLStreamWriter writer) throws XMLStreamException {
    XMLStreamWriterHelper.writeStartResource(writer, idno, null);
    XMLStreamWriterHelper.writeStartResourceFragment(writer, null, null);
    /*
        * NOTE: use only AdvancedDataViewWriter, even if we are only doing
        * legacy/simple FCS.
        * The AdvancedDataViewWriter instance could also be
        * reused, by calling reset(), if it was used in a smarter fashion.
        */
    AdvancedDataViewWriter helper = new AdvancedDataViewWriter(AdvancedDataViewWriter.Unit.ITEM);
    URI layerId = URI.create("http://endpoint.example.org/Layers/orth1");
    String[] words;
    long start = 1;
    if ((left != null) && !left.isEmpty()) {
        words = left.split("\\s+");
        for (int i = 0; i < words.length; i++) {
            long end = start + words[i].length();
            helper.addSpan(layerId, start, end, words[i]);
            start = end + 1;
        }
    }
    words = keyword.split("\\s+");
    for (int i = 0; i < words.length; i++) {
        long end = start + words[i].length();
        helper.addSpan(layerId, start, end, words[i], 1);
        start = end + 1;
    }
    if ((right != null) && !right.isEmpty()) {
        words = right.split("\\s+");
        for (int i = 0; i < words.length; i++) {
            long end = start + words[i].length();
            helper.addSpan(layerId, start, end, words[i]);
            start = end + 1;
        }
    }
    helper.writeHitsDataView(writer, layerId);
    if (advancedFCS) {
        helper.writeAdvancedDataView(writer);
    }
    XMLStreamWriterHelper.writeEndResourceFragment(writer);
    XMLStreamWriterHelper.writeEndResource(writer);
}