solrconfig.xml

<updateRequestProcessorChain name="classification" default="true" >
  <processor class="solr.ClassificationUpdateProcessorFactory">
    <str name="inputFields">content</str>
    <str name="classField">group</str>
    <str name="algorithm">knn</str>
    <str name="knn.k">3</str>
    <str name="knn.minTf">1</str>
    <str name="knn.minDf">5</str>
  </processor>
   <processor class="solr.LogUpdateProcessorFactory" />
  <processor class="solr.RunUpdateProcessorFactory"/>
</updateRequestProcessorChain>


<initParams path="/update/**,/query,/select,/tvrh,/elevate,/spell,/browse">
  <lst name="defaults">
    <str name="df">_text_</str>
    <str name="update.chain">classification</str>
  </lst>
</initParams>


<updateProcessor class="solr.ClassificationUpdateProcessorFactory" name="classification-test">
  <str name="inputFields">content</str>
  <str name="classField">group</str>
  <str name="predictedClassField">group_predicted</str>
  <str name="algorithm">knn</str>
  <str name="knn.k">3</str>
  <str name="knn.minTf">1</str>
  <str name="knn.minDf">5</str>
</updateProcessor>

<!-- overwriting existing chain -->
<updateRequestProcessorChain name="add-unknown-fields-to-the-schema" default="${update.autoCreateFields:true}"
         processor="uuid,remove-blank,field-name-mutating,parse-boolean,parse-long,parse-double,parse-date,add-schema-fields,classification-test">
  <processor class="solr.LogUpdateProcessorFactory"/>
  <processor class="solr.DistributedUpdateProcessorFactory"/>
  <processor class="solr.RunUpdateProcessorFactory"/>
</updateRequestProcessorChain>