Replace OutputServiceMJImpl#countByType() with old version

The new implementation of `OutputServiceMJImpl#countByType()` didn't work at all
and was using aggregations which are only supported since MongoDB 2.2 and we need
to support MongoDB 2.0 as well.

The error in the new implementation using aggregations was:

com.mongodb.CommandFailureException: { "serverUsed" : "127.0.0.1:27017" , "errmsg" : "exception: A pipeline stage specification object must contain exactly one field." , "code" : 16435 , "ok" : 0.0}

graylog2-server/src/main/java/org/graylog2/streams/OutputServiceMJImpl.java

@@ -16,10 +16,10 @@
  */
 package org.graylog2.streams;
 
-import com.google.common.collect.Maps;
 import com.google.common.collect.Sets;
 import com.mongodb.BasicDBObject;
 import com.mongodb.DBCollection;
+import com.mongodb.DBCursor;
 import com.mongodb.DBObject;
 import org.bson.types.ObjectId;
 import org.graylog2.bindings.providers.MongoJackObjectMapperProvider;
@@ -29,22 +29,21 @@
 import org.graylog2.plugin.Tools;
 import org.graylog2.plugin.database.ValidationException;
 import org.graylog2.plugin.streams.Output;
-import org.graylog2.plugin.streams.Stream;
 import org.graylog2.rest.models.streams.outputs.requests.CreateOutputRequest;
-import org.mongojack.Aggregation;
-import org.mongojack.AggregationResult;
 import org.mongojack.DBQuery;
 import org.mongojack.DBUpdate;
 import org.mongojack.JacksonDBCollection;
 import org.mongojack.WriteResult;
 
 import javax.inject.Inject;
+import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
 import java.util.Set;
 
 public class OutputServiceMJImpl implements OutputService {
     private final JacksonDBCollection<OutputAVImpl, String> coll;
+    private final DBCollection dbCollection;
     private final StreamService streamService;
 
     @Inject
@@ -53,7 +52,7 @@ public OutputServiceMJImpl(MongoConnection mongoConnection,
                                StreamService streamService) {
         this.streamService = streamService;
         final String collectionName = OutputAVImpl.class.getAnnotation(CollectionName.class).value();
-        final DBCollection dbCollection = mongoConnection.getDatabase().getCollection(collectionName);
+        this.dbCollection = mongoConnection.getDatabase().getCollection(collectionName);
         this.coll = JacksonDBCollection.wrap(dbCollection, OutputAVImpl.class, String.class, mapperProvider.get());
     }
 
@@ -110,23 +109,19 @@ public long count() {
 
     @Override
     public Map<String, Long> countByType() {
-        final DBObject groupFields = new BasicDBObject("_id", "$type");
-        groupFields.put("count", new BasicDBObject("$sum", 1));
-        final DBObject countOperation = new BasicDBObject("$group", groupFields);
-
-        final AggregationResult<TypeCountResult> aggregationResult = coll.aggregate(new Aggregation<>(TypeCountResult.class, countOperation, new BasicDBObject()));
-
-        final Map<String, Long> result = Maps.newHashMap();
-
-        for (TypeCountResult typeResult : aggregationResult.results())
-            result.put(typeResult.type, typeResult.count);
-
-        return result;
-    }
+        final DBCursor outputTypes = dbCollection.find(null, new BasicDBObject(OutputImpl.FIELD_TYPE, 1));
+
+        final Map<String, Long> outputsCountByType = new HashMap<>(outputTypes.count());
+        for (DBObject outputType : outputTypes) {
+            final String type = (String) outputType.get(OutputImpl.FIELD_TYPE);
+            if (type != null) {
+                final Long oldValue = outputsCountByType.get(type);
+                final Long newValue = (oldValue == null) ? 1 : oldValue + 1;
+                outputsCountByType.put(type, newValue);
+            }
+        }
 
-    class TypeCountResult {
-        String type;
-        Long count;
+        return outputsCountByType;
     }
 
     private OutputAVImpl implOrFail(Output output) {