SolrPlugins

Solr Plugins

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

  1. Solr Plugins
  2. How to Load Plugins
    1. The Old Way
  3. Building Plugins
  4. Classes that are 'Pluggable'
    1. Request Processing
      1. SolrRequestHandler
      2. SearchComponent
      3. QueryResponseWriter
      4. Similarity
      5. CacheRegenerator
    2. Fields
      1. Analyzer
      2. Tokenizer and TokenFilter
      3. FieldType
    3. Internals
      1. SolrCache
      2. SolrEventListener
      3. UpdateHandler
  5. Plugin Initialization
    1. ResourceLoaderAware
    2. SolrCoreAware
    3. Lifecycle

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. In the example program, the location is example/solr/lib. This directory does not exist in the distribution, so you would need to do mkdir for the first time.

This feature for loading plugins uses a custom Class Loader. It has been tested with a variety of Servlet Containers, but given the multitudes of servlet containers available in the wild it may not always work with every servlet container.

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.

Building Plugins

To develop your own plugins, add the apache-solr-*.jar jar files to the classpath you use to compile your code. They contains all of the Solr Interfaces and Class files you may need. If you are developing plugins that know about lower level Lucene interfaces, you may need to also include the lucene-*.jar jar files from the lib/ directory of your Solr distribution.

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.

Request Processing

SolrRequestHandler

Instances of [WWW] 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 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>
     <lst>
     <int name="someConfigValue">42</int>
  </requestHandler>

for more info, see: SolrRequestHandler

SearchComponent

<!> Solr1.3

Instances of [WWW] SearchComponent define logic that is registered to SolrCore and is executed by a given SolrRequestHandler typically to supplement a result set. The following components are available by default: 

<searchComponent name="query"     class="org.apache.solr.handler.component.QueryComponent" />
<searchComponent name="facet"     class="org.apache.solr.handler.component.FacetComponent" />
<searchComponent name="mlt"       class="org.apache.solr.handler.component.MoreLikeThisComponent" />
<searchComponent name="highlight" class="org.apache.solr.handler.component.HighlightComponent" />
<searchComponent name="debug"     class="org.apache.solr.handler.component.DebugComponent" />

Multiple search components can be added to a given SolrRequestHandler. Components and their configuration can be specified in your solrconfig.xml... 

<searchComponent name="elevator" class="org.apache.solr.handler.component.QueryElevationComponent" >
  <!-- pick a fieldType to analyze queries -->
  <str name="queryFieldType">string</str>
  <str name="config-file">elevate.xml</str>
</searchComponent>
 
<requestHandler name="/elevate" class="org.apache.solr.handler.component.SearchHandler" startup="lazy">
  <lst name="defaults">
    <str name="echoParams">explicit</str>
  </lst>
  <!--
  By default, this will register the following components:
    
  <arr name="components">
    <str>query</str>
    <str>facet</str>
    <str>mlt</str>
    <str>highlight</str>
    <str>debug</str>
  </arr>
    
  To insert handlers before or after the 'standard' components, use:
  
  <arr name="first-components">
    <str>first</str>
  </arr>

  We insert the elevator component after all the defaults
  -->
  <arr name="last-components">
    <str>elevator</str>
  </arr>
</requestHandler>

for more info, see: SearchComponent

QueryResponseWriter

Instances of [WWW] 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 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>
  </queryResponseWriter>

Similarity

The [WWW] Similarity class is a native Lucene concept that determines how much of the 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 [WWW] Lucene scoring documentation. If you wish to override the DefaultSimilarity provided by Lucene, you can specify your own subclass in your schema.xml... 

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

CacheRegenerator

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

    <cache name="myCustomCacheInstance"
      class="solr.LRUCache"
      size="4096"
      initialSize="1024"
      autowarmCount="1024"
      regenerator="my.package.CustomCacheRegenerator"
      />

Fields

Analyzer

The [WWW] Analyzer class is a native Lucene concept that determines how tokens are produced from a piece of text. Solr allows Analyzers to be specified for each fieldtype in your schema.xml that uses the TextField class -- and even allows for different Analyzers to be specified for indexing text as documents are added, and parsing text specified in a query... 

    <fieldtype name="text_foo" class="solr.TextField">
      <analyzer class="my.package.CustomAnalyzer"/>
    </fieldType>
    <fieldtype name="text_bar" class="solr.TextField">
      <analyzer type="index" class="my.package.CustomAnalyzerForIndexing"/>
      <analyzer type="query" class="my.package.CustomAnalyzerForQuering"/>
    </fieldType>

Solr also provides a [WWW] SolrAnalyzer base class which can be used if you want to write your own Analyzer and configure the "positionIncrementGap" in your schema.xml... 

    <fieldtype name="text_baz" class="solr.TextField" positionIncrementGap="100">
      <analyzer class="my.package.CustomSolrAnalyzer" />
    </fieldType>

Specifying an Analyzer class in your schema.xml makes a lot of sense if you already have an existing Analyzer you wish to use as is, but if you are planning to write Analysis code from scratch that you would like to use in Solr, you should keep reading the following sections...

Tokenizer and TokenFilter

In addition to specifing specific Analyzer classes, Solr can construct Analyzers on the fly for each field type using a [WWW] Tokenizer and any number of [WWW] TokenFilters. To take advantage of this functionality with any Tokenizers or TokenFilters you may have (or may want to implement) you'll need to provide a [WWW] TokenizerFactory and [WWW] TokenFilterFactory which takes care of any initialization and configuration, and specify these Factories in your schema.xml... 

    <fieldtype name="text_zop" class="solr.TextField" positionIncrementGap="100">
      <analyzer>
          <tokenizer class="my.package.CustomTokenizerFactory"/>
          <!-- this TokenFilterFactory has custom options -->
          <filter class="my.package.CustomTokenFilter" optA="yes" optB="maybe" optC="42.5"/>
          <!-- Solr has many existing FilterFactories that you can reuse -->
          <filter class="solr.StopFilterFactory" ignoreCase="true"/>
      </analyzer>
    </fieldtype>

FieldType

If you have very specialized data type needs, you can specify your own [WWW] FieldType class for each <fieldtype> you declare in your schema.xml, to control how the values for those fields are encoded in your index... 

    <fieldtype name="wacko" class="my.package.CustomFieldType" />

Internals

SolrCache

The [WWW] SolrCache API allows you to specify custom Cache implementations for any of the various caches you might declare in your solrconfig.xml... 

    <filterCache       class="my.package.CustomCache"          size="512" />
    <queryResultsCache class="my.package.CustomCache"          size="512"  />
    <documentCache     class="my.package.AlternateCustomCache" size="512"  />

SolrEventListener

Instances of the [WWW] SolrEventListener Interface can be configured in your solrconfig.xml to be be executed any time specific events occur within Solr (currently, the only events that can be "listened" for are firstSearcher and newSearcher)... 

    <listener event="newSearcher" class="my.package.CustomEventListener">
      <-- init args for the EventListener instance can be specified here -->
      <lst name="arg1">
        <str name="q">solr</str> <str name="start">0</str> <str name="rows">10</str>
      </lst>
      <int name="otherArg">42</int>
    </listener>

UpdateHandler

The [WWW] UpdateHandler API allows you to specify a custom algorithm for determining how sequences of adds and deletes are processed by Solr. The UpdateHandler you wish to use can be configured in your solrconfig.xml, but implementing a new UpdateHandler is considered extremely advanced and is not recommended.... 

  <updateHandler class="my.package.CustomUpdateHandler">

Plugin Initialization

<!> Solr1.3

Plugins are initializes either with [WWW] init( Map<String,String> args ) or [WWW] init( NamedList args ).

ResourceLoaderAware

Classes that need to know about the [WWW] ResourceLoader can implement [WWW] ResourceLoaderAware. Valid ResourceLoaderAware include:

SolrCoreAware

Classes that need to know about the [SolrCore] can implement [WWW] SolrCoreAware. Valid SolrCoreAware classes include:

Lifecycle

The initialization lifecycle is:

  1. Constructor

  2. init( Map / NamedList )

  3. ResourceLoaderAware classes call: inform( ResourceLoader );

  4. Before the first request is made and after all plugins have been created and registered, SolrCoreAware plugins call: inform( SolrCore );

last edited 2008-04-24 16:12:15 by TriciaWilliams