问题
I have problem using group feature of solr. I simply can't use the feature. Here is the description of the problem.
The group field that I use is defined as follows.
field name="clusterid" type="string" indexed="true" stored="true" multiValued="false"
The indexed "clusterid" field has valid values.
Initially, I tried using "group" feature using Solrj client API on the above field. I started getting "HTTP status 500 Internal Server Errors..." Assuming that the syntax or the ordering of the parameters could be an issue, I decided to test the same feature using firefox browser.
.../solr/select/?q=title%3Acomputer
yields a nice set of results with valid clusterid(s).
However, when I try to group the results using the clusterid field, I get a null pointer exception. Here is the url that was used for grouping
.../solr/select/?q=title%3Acomputer&group=true&group.field=clusterid
and the response was
type Status report
message null java.lang.NullPointerException at org.apache.solr.handler.clustering.ClusteringComponent.process(ClusteringComponent.java:89) at org.apache.solr.handler.component.SearchHandler.handleRequestBody(SearchHandler.java:186) at org.apache.solr.handler.RequestHandlerBase.handleRequest(RequestHandlerBase.java:129) at org.apache.solr.core.SolrCore.execute(SolrCore.java:1376) at org.apache.solr.servlet.SolrDispatchFilter.execute(SolrDispatchFilter.java:365) at org.apache.solr.servlet.SolrDispatchFilter.doFilter(SolrDispatchFilter.java:260) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206) at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233) at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191) at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127) at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102) at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109) at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:298) at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:852) at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:588) at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:489) at java.lang.Thread.run(Thread.java:662)
Note: I use the solr version 3.6.2 on Windows XP. The solrconfig file has changes only for the memory settings (increase value) from the default ones.
When I tried to use a multivalued field as group field, the response message was very clear that "multiValued" fields can not be used for grouping. When I tested with non-string fields, again I got responses that those were not string fields etc.
But when a field of string type (either clusterid or any other field that is of string type) was provided -- null pointer exception was thrown.
Do I miss anything that is obvious (in the schema or the solrconfig file)?
回答1:
I'm facing the same issue using Solr 6.3. It appears the clustering component (which you are apparently using) is unable to extract the data it needs from a group response. The only workaround I found is to enable highlighting, then clustering appears to work; but this comes with a significant performance penalty. However if your result size is small it may be an option for you; for larger results (> 200-300 docs), clustering appears to be taking more time than highlighting anyway. I'm using the Lingo algorithm, maybe with STC it would be better.
来源：https://stackoverflow.com/questions/14757022/solr-group-field-nullpointer-exception