private void emitSolrBatch(List<SolrInputDocument> docsToUpdate)
            throws IOException, TikaEmitterException {
        if (LOG.isDebugEnabled()) {
            LOG.debug("Emitting solr doc batch: {}", docsToUpdate);
        }
        if (!docsToUpdate.isEmpty()) {
            try {
                UpdateRequest req = new UpdateRequest();
                req.add(docsToUpdate);
                req.setCommitWithin(commitWithin);
                req.setParam("failOnVersionConflicts", "false");
                UpdateResponse updateResponse = req.process(solrClient, solrCollection);
                LOG.debug("update response: " + updateResponse);
                if (updateResponse.getStatus() != 0) {
                    throw new TikaEmitterException("Bad status: " + updateResponse);
                }
            } catch (Exception e) {
                throw new TikaEmitterException("Could not add batch to solr", e);
            }
        }
    }
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