"ArrayList cannot be cast to java.lang.String" error message on Solr DIH endpoints

Question

I am setting up a new Solr server and I'm running into an issue I haven't experienced in previous Solr installations. When I navigate to a core's "Dataimport" tab (without even triggering an import request), several of the HTTP requests made by the admin UI fail. Checking the Solr logs, I see this stacktrace:

java.lang.ClassCastException: java.util.Arrays$ArrayList cannot be cast to java.lang.String
    at org.apache.solr.handler.dataimport.RequestInfo.<init>(RequestInfo.java:52)
    at org.apache.solr.handler.dataimport.DataImportHandler.handleRequestBody(DataImportHandler.java:131)
    at org.apache.solr.handler.RequestHandlerBase.handleRequest(RequestHandlerBase.java:195)
    at org.apache.solr.core.SolrCore.execute(SolrCore.java:2503)
    at org.apache.solr.servlet.HttpSolrCall.execute(HttpSolrCall.java:711)
    at org.apache.solr.servlet.HttpSolrCall.call(HttpSolrCall.java:517)
    at org.apache.solr.servlet.SolrDispatchFilter.doFilter(SolrDispatchFilter.java:384)
    at org.apache.solr.servlet.SolrDispatchFilter.doFilter(SolrDispatchFilter.java:330)
    at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1629)
    at org.eclipse.jetty.servlet.ServletHandler.doHandle(ServletHandler.java:533)
    at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:143)
    at org.eclipse.jetty.security.SecurityHandler.handle(SecurityHandler.java:548)
    at org.eclipse.jetty.server.handler.HandlerWrapper.handle(HandlerWrapper.java:132)
    at org.eclipse.jetty.server.handler.ScopedHandler.nextHandle(ScopedHandler.java:190)
    at org.eclipse.jetty.server.session.SessionHandler.doHandle(SessionHandler.java:1595)
    at org.eclipse.jetty.server.handler.ScopedHandler.nextHandle(ScopedHandler.java:188)
    at org.eclipse.jetty.server.handler.ContextHandler.doHandle(ContextHandler.java:1253)
    at org.eclipse.jetty.server.handler.ScopedHandler.nextScope(ScopedHandler.java:168)
    at org.eclipse.jetty.servlet.ServletHandler.doScope(ServletHandler.java:473)
    at org.eclipse.jetty.server.session.SessionHandler.doScope(SessionHandler.java:1564)
    at org.eclipse.jetty.server.handler.ScopedHandler.nextScope(ScopedHandler.java:166)
    at org.eclipse.jetty.server.handler.ContextHandler.doScope(ContextHandler.java:1155)
    at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:141)
    at org.eclipse.jetty.server.handler.ContextHandlerCollection.handle(ContextHandlerCollection.java:219)
    at org.eclipse.jetty.server.handler.HandlerCollection.handle(HandlerCollection.java:126)
    at org.eclipse.jetty.server.handler.HandlerWrapper.handle(HandlerWrapper.java:132)
    at org.eclipse.jetty.rewrite.handler.RewriteHandler.handle(RewriteHandler.java:335)
    at org.eclipse.jetty.server.handler.HandlerWrapper.handle(HandlerWrapper.java:132)
    at org.eclipse.jetty.server.Server.handle(Server.java:530)
    at org.eclipse.jetty.server.HttpChannel.handle(HttpChannel.java:347)
    at org.eclipse.jetty.server.HttpConnection.onFillable(HttpConnection.java:256)
    at org.eclipse.jetty.io.AbstractConnection$ReadCallback.succeeded(AbstractConnection.java:279)
    at org.eclipse.jetty.io.FillInterest.fillable(FillInterest.java:102)
    at org.eclipse.jetty.io.ChannelEndPoint$2.run(ChannelEndPoint.java:124)
    at org.eclipse.jetty.util.thread.strategy.EatWhatYouKill.doProduce(EatWhatYouKill.java:247)
    at org.eclipse.jetty.util.thread.strategy.EatWhatYouKill.produce(EatWhatYouKill.java:140)
    at org.eclipse.jetty.util.thread.strategy.EatWhatYouKill.run(EatWhatYouKill.java:131)
    at org.eclipse.jetty.util.thread.ReservedThreadExecutor$ReservedThread.run(ReservedThreadExecutor.java:382)
    at org.eclipse.jetty.util.thread.QueuedThreadPool.runJob(QueuedThreadPool.java:708)
    at org.eclipse.jetty.util.thread.QueuedThreadPool$2.run(QueuedThreadPool.java:626)
    at java.lang.Thread.run(Thread.java:748)

This same error occurs when I begin a data import from the Admin UI, or really any HTTP request made to the /solr/<core>/dataimport* endpoint.

I dug through the source and found the line where this is happening: https://github.com/apache/lucene-solr/blob/1d85cd783863f75cea133fb9c452302214165a4d/solr/contrib/dataimporthandler/src/java/org/apache/solr/handler/dataimport/RequestInfo.java#L52

if (requestParams.containsKey("command")) { 
    command = (String) requestParams.get("command");
}

My best guess is that the command parameter is somehow being included twice in request and is coming through as an ArrayList instead of a String. In my solrconfig.xml, I define my dataimportfull handler like so:

<requestHandler name="/dataimportfull" class="solr.DataImportHandler">
    <lst name="defaults">
        <str name="config">./DIHconfig.xml</str>
        <str name="echoParams">explicit</str>
        <str name="wt">json</str>
        <str name="indent">true</str>
        <str name="importType">full</str>
        <str name="command">full-import</str>
        <str name="commit">true</str>
        <str name="clean">true</str>
        <str name="update.chain">add-unknown-fields-to-the-schema</str>
    </lst>
</requestHandler>

I tried removing the "command" line, but the error still occurred.

The main difference between this Solr instance and other Solr servers I've set up is that this instance is running inside of a Windows Server 2016 Docker container, using an image based on openjdk:8-jdk-windowsservercore-ltsc2016. Inside this container, I'm running Solr 7.3.1.

Any ideas about what might be causing this error?

Answer 1

Figured it out. There was nothing wrong with my Solr setup. Instead, it was a problem with the reverse proxy (IIS) sitting in front of Solr. The way I was proxying traffic to Solr was duplicating all of the query parameters.

Here's the question and answer that helped me fix the issue: IIS URL Rewrite module repeats query string.