Using SolrJ

Building and Running SolrJ Applications

The SolrJ API ships with Solr, so you do not have to download or install anything else. But you will need to configure your build to include SolrJ and its dependencies.

<dependency org="org.apache.solr" name="solr-solrj" rev="8.2.0"/>

<dependency>
  <groupId>org.apache.solr</groupId>
  <artifactId>solr-solrj</artifactId>
  <version>8.2.0</version>
</dependency>

compile group: 'org.apache.solr', name: 'solr-solrj', version: '8.2.0'

javac -cp .:$SOLR_HOME/dist/solr-solrj-8.2.0.jar ...

java -cp .:$SOLR_HOME/dist/solrj-lib/*:$SOLR_HOME/dist/solr-solrj-8.2.0.jar ...

SolrJ Overview

For all its flexibility, SolrJ is built around a few simple interfaces.

All requests to Solr are sent by a SolrClient. SolrClient’s are the main workhorses at the core of SolrJ. They handle the work of connecting to and communicating with Solr, and are where most of the user configuration happens.

Requests are sent in the form of SolrRequests, and are returned as SolrResponses.

final String solrUrl = "http://localhost:8983/solr";
return new HttpSolrClient.Builder(solrUrl)
    .withConnectionTimeout(10000)
    .withSocketTimeout(60000)
    .build();

Querying in SolrJ

SolrClient has a number of query() methods for fetching results from Solr. Each of these methods takes in a SolrParams,an object encapsulating arbitrary query-parameters. And each method outputs a QueryResponse, a wrapper which can be used to access the result documents and other related metadata.

The following snippet uses a SolrClient to query Solr’s "techproducts" example collection, and iterate over the results.

final SolrClient client = getSolrClient();

final Map<String, String> queryParamMap = new HashMap<String, String>();
queryParamMap.put("q", "*:*");
queryParamMap.put("fl", "id, name");
queryParamMap.put("sort", "id asc");
MapSolrParams queryParams = new MapSolrParams(queryParamMap);

final QueryResponse response = client.query("techproducts", queryParams);
final SolrDocumentList documents = response.getResults();

print("Found " + documents.getNumFound() + " documents");
for(SolrDocument document : documents) {
  final String id = (String) document.getFirstValue("id");
  final String name = (String) document.getFirstValue("name");

  print("id: " + id + "; name: " + name);
}

SolrParams has a SolrQuery subclass, which provides some convenience methods that greatly simplifies query creation. The following snippet shows how the query from the previous example can be built using some of the convenience methods in SolrQuery:

final SolrQuery query = new SolrQuery("*:*");
query.addField("id");
query.addField("name");
query.setSort("id", ORDER.asc);
query.setRows(numResultsToReturn);

Indexing in SolrJ

Indexing is also simple using SolrJ. Users build the documents they want to index as instances of SolrInputDocument, and provide them as arguments to one of the add() methods on SolrClient.

The following example shows how to use SolrJ to add a document to Solr’s "techproducts" example collection:

final SolrClient client = getSolrClient();

final SolrInputDocument doc = new SolrInputDocument();
doc.addField("id", UUID.randomUUID().toString());
doc.addField("name", "Amazon Kindle Paperwhite");

final UpdateResponse updateResponse = client.add("techproducts", doc);
// Indexed documents must be committed
client.commit("techproducts");

Java Object Binding

While the UpdateResponse and QueryResponse interfaces that SolrJ provides are useful, it is often more convenient to work with domain-specific objects that can more easily be understood by your application. Thankfully, SolrJ supports this by implicitly converting documents to and from any class that has been specially marked with Field annotations.

Each instance variable in a Java object can be mapped to a corresponding Solr field, using the Field annotation. The Solr field shares the name of the annotated variable by default, however, this can be overridden by providing the annotation with an explicit field name.

The example snippet below shows an annotated TechProduct class that can be used to represent results from Solr’s "techproducts" example collection.

public static class TechProduct {
  @Field public String id;
  @Field public String name;

  public TechProduct(String id, String name) {
    this.id = id;  this.name = name;
  }

  public TechProduct() {}
}

Application code with access to the annotated TechProduct class above can index TechProduct objects directly without any conversion, as in the example snippet below:

final SolrClient client = getSolrClient();

final TechProduct kindle = new TechProduct("kindle-id-4", "Amazon Kindle Paperwhite");
final UpdateResponse response = client.addBean("techproducts", kindle);

client.commit("techproducts");

Similarly, search results can be converted directly into bean objects using the getBeans() method on QueryResponse:

final SolrClient client = getSolrClient();

final SolrQuery query = new SolrQuery("*:*");
query.addField("id");
query.addField("name");
query.setSort("id", ORDER.asc);

final QueryResponse response = client.query("techproducts", query);
final List<TechProduct> products = response.getBeans(TechProduct.class);

Other APIs

SolrJ allows more than just querying and indexing. It supports all of Solr’s APIs. Accessing Solr’s other APIs is as easy as finding the appropriate request object, providing any necessary parameters, and passing it to the request() method of your SolrClient. request() will return a NamedList: a generic object which mirrors the hierarchical structure of the JSON or XML returned by their request.

The example below shows how SolrJ users can call the CLUSTERSTATUS API of SolrCloud deployments, and manipulate the returned NamedList:

final SolrClient client = getSolrClient();

final SolrRequest request = new CollectionAdminRequest.ClusterStatus();

final NamedList<Object> response = client.request(request);
final NamedList<Object> cluster = (NamedList<Object>) response.get("cluster");
final List<String> liveNodes = (List<String>) cluster.get("live_nodes");

print("Found " + liveNodes.size() + " live nodes");