Solr Plugins

Solr allows you to load custom code to perform a variety of of tasks within Solr -- from custom custom Request Handlers to process your searches, to custom Analyzers and Token Filters for your text field, even custom Field Types. TableOfContents

How to Load Plugins

Plugin code can be loaded into Solr by putting Jars containing your classes in a lib directory in your Solr Home directory prior to starting your servlet container.

This is a relatively new feature (as of 2006-11-13) which uses a custom Class Loader. It's not yet clear exactly how successful this approach works on the multitudes of servlet containers available in the wild.

The Old Way

Another method that works consistently on any servlet container is to:

  1. unpack the solr.war
  2. add a jar containing your custom classes to the WEB-INF/lib directory

  3. repack your new, customized, solr.war and use it.

List of Classes that are 'Pluggable'

The following is a complete list of every API that can be treated as a plugin in Solr, with information on how to use that configure your Solr instance to use an instance of that class.

/!\ :TODO: /!\ for each class, link to javadocs and show example of where/how to configure usage

Request Processing


Instances of [ SolrRequestHandler] define the logic that is executed for any request. Multiple handlers (including multiple instances of the same SolrRequestHandler class with different configurations) can be specified in your [wiki:SolrConfigXml solrconfig.xml]...

  <requestHandler name="foo" class="my.package.CustomRequestHandler" />
  <requestHandler name="bar" class="my.package.AnotherCustomRequestHandler" />
  <requestHandler name="baz" class="my.package.AnotherCustomRequestHandler">
    <!-- initialization args may optionally be defined here -->
     <lst name="defaults">
       <int name="rows">10</int>
       <str name="fl">*</str>
       <str name="version">2.1</str>
     <int name="someConfigValue">42</int>


Instances of [ QueryResponseWriter] define the formatting used to output the results of a request. Multiple writers (including multiple instances of the same QueryResponseWriter class with different configurations) can be specified in your [wiki:SolrConfigXml solrconfig.xml]...

  <queryResponseWriter name="wow" class="my.package.CustomResponseWriter" />
  <queryResponseWriter name="woz" class="my.package.AnotherCustomResponseWriter" />
  <queryResponseWriter name="woz" class="my.package.AnotherCustomResponseWriter" >
    <!-- initialization args may optionally be defined here -->
    <int name="someConfigValue">42</int>


The [ Similarity] is a native lucene concept that determines how much of hte score calculations for the various types of queries are executed. For more information on how the methods in the Similarity class are used, consult the [ Lucene scoring documentation]. If you wish to override the DefaultSimilarity provided by Lucene, you can specify your own subclass in your [wiki:SchemaXml schema.xml]...

  <similarity class="my.package.CustomSimilarity"/>


The [ CacheRegenerator] API allows people who are writing custom SolrRequestHandlers which utilize custom [wiki:SolrCaching User Caches] to specify how those caches should be populated during autowarming. A regenerator class can be specified hen the cache is declared in your [wiki:SolrConfigXml solrconfig.xml]...

    <cache name="myCustomCacheInstance"