SolrJ - NPE when accessing to SolrCloud - solrj

Question

I'm running the following test code on SolrCloud using Solrj library:
public static void main(String[] args) {
String zkHostString = "192.168.56.99:2181";
SolrClient solr = new CloudSolrClient.Builder().withZkHost(zkHostString).build();
List<MyBean> beans = new ArrayList<>();
for(int i = 0; i < 10000 ; i++) {
// creating a bunch of MyBean to be indexed
// and temporarily storing them in a List
// no Solr operations performed here
}
System.out.println("Adding...");
try {
solr.addBeans("myCollection", beans);
} catch (IOException | SolrServerException e1) {
// TODO Auto-generated catch block
e1.printStackTrace();
}
System.out.println("Committing...");
try {
solr.commit("myCollection");
} catch (SolrServerException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
This code fails due to the following exception
Exception in thread "main" java.lang.NullPointerException
at org.apache.solr.client.solrj.impl.CloudSolrClient.requestWithRetryOnStaleState(CloudSolrClient.java:1175)
at org.apache.solr.client.solrj.impl.CloudSolrClient.request(CloudSolrClient.java:1057)
at org.apache.solr.client.solrj.SolrRequest.process(SolrRequest.java:160)
at org.apache.solr.client.solrj.SolrClient.add(SolrClient.java:106)
at org.apache.solr.client.solrj.SolrClient.addBeans(SolrClient.java:357)
at org.apache.solr.client.solrj.SolrClient.addBeans(SolrClient.java:312)
at com.togather.solr.testing.SolrIndexingTest.main(SolrIndexingTest.java:83)
This is the full stacktrace of the exception. I just "upgraded" from a Solr standalone installation to a SolrCloud (with an external Zookeeper single instance, not the embedded one). With standalone Solr the same code (with just some minor differences, like the host URL) used to work perfectly.
The NPE sends me inside the SolrJ library, which I don't know.
Anyone can help me understand where the problem originates from and how I can overcome it? Due to my unexperience and the brevity of the error message, I can't figure out where to start inquiring from.

Answer 1

Looking at your code, I would suggest to specify the default collection as first thing.
CloudSolrClient solr = new CloudSolrClient.Builder().withZkHost(zkHostString).build();
solr.setDefaultCollection("myCollection");
Regarding the NPE you're experiencing, very likely is due to a network error.
In these lines your exception is raised by for loop: for (DocCollection ext : requestedCollections)
if (wasCommError) {
// it was a communication error. it is likely that
// the node to which the request to be sent is down . So , expire the state
// so that the next attempt would fetch the fresh state
// just re-read state for all of them, if it has not been retired
// in retryExpiryTime time
for (DocCollection ext : requestedCollections) {
ExpiringCachedDocCollection cacheEntry = collectionStateCache.get(ext.getName());
if (cacheEntry == null) continue;
cacheEntry.maybeStale = true;
}
if (retryCount < MAX_STALE_RETRIES) {//if it is a communication error , we must try again
//may be, we have a stale version of the collection state
// and we could not get any information from the server
//it is probably not worth trying again and again because
// the state would not have been updated
return requestWithRetryOnStaleState(request, retryCount + 1, collection);
}
}