@Override
    public void emit(String emitKey, List<Metadata> metadataList, ParseContext parseContext)
            throws IOException, TikaEmitterException {
        if (metadataList == null || metadataList.size() == 0) {
            LOG.warn("metadataList is null or empty");
            return;
        }
        List<SolrInputDocument> docsToUpdate = new ArrayList<>();
        addMetadataAsSolrInputDocuments(emitKey, metadataList, docsToUpdate);
        emitSolrBatch(docsToUpdate);
    }
You can specify solrUrls, or you can specify solrZkHosts and use use zookeeper to determine the solr server urls.
tika-pipes/tika-emitters/tika-emitter-solr/src/main/java/org/apache/tika/pipes/emitter/solr/SolrEmitter.java