Uses $group aggregator to get last stroke number rather than looping through all strokes

src/main/java/com/henrypump/poc/Database.java

@@ -6,8 +6,11 @@ package com.henrypump.poc;
 
 import com.mongodb.*;
 
+import com.mongodb.client.AggregateIterable;
 import com.mongodb.client.MongoDatabase;
 import com.mongodb.client.MongoCollection;
+import com.mongodb.client.model.Accumulators;
+import com.mongodb.client.model.Aggregates;
 
 import com.mongodb.client.model.Sorts;
 import org.bson.Document;
@@ -19,6 +22,7 @@ import static com.mongodb.client.model.Filters.*;
 
 import javax.print.Doc;
 import java.util.ArrayList;
+import java.util.Arrays;
 import java.util.Date;
 import java.util.List;
 public class Database {
@@ -32,17 +36,25 @@ public class Database {
     }
 
     public long getLastStrokeNum(){
-        MongoCollection<Document> collection = database.getCollection("cards");
-        MongoCursor<Document> cursor = collection.find().iterator();
+
         long lastStroke = 0;
+
+        MongoCollection<Document> collection = database.getCollection("cards");
+        MongoCursor<Document> cursor = collection.aggregate(
+                Arrays.asList(
+                        Aggregates.group("strokeNumber", Accumulators.last("lastStroke", "$strokeNumber"))
+                )
+        ).iterator();
+
         try {
             while (cursor.hasNext()) {
-                long docStroke = (Long) cursor.next().get("strokeNumber");
+                long docStroke = cursor.next().getLong("lastStroke");
                 if (docStroke  > lastStroke) { lastStroke = docStroke; }
             }
         } finally {
             cursor.close();
         }
+        System.out.println("Found last stroke to be " + lastStroke);
         return lastStroke;
     }