From 93bd5183e20552630804ea996e7d816a0414e95d Mon Sep 17 00:00:00 2001
From: Brian Lowe <brian@ontocale.com>
Date: Tue, 6 Apr 2021 17:15:50 +0300
Subject: [PATCH] Move event listening to RDFServiceGraph level to avoid adding
 a new redundant listener each time a model is made for an existing
 RDFServiceGraph. Resolve https://jira.lyrasis.org/browse/VIVO-1976

---
 .../webapp/dao/jena/RDFServiceGraph.java      | 32 +++++-----
 .../webapp/dao/jena/RDFServiceGraphTest.java  | 62 +++++++++++++++++++
 2 files changed, 76 insertions(+), 18 deletions(-)
 create mode 100644 api/src/test/java/edu/cornell/mannlib/vitro/webapp/dao/jena/RDFServiceGraphTest.java

diff --git a/api/src/main/java/edu/cornell/mannlib/vitro/webapp/dao/jena/RDFServiceGraph.java b/api/src/main/java/edu/cornell/mannlib/vitro/webapp/dao/jena/RDFServiceGraph.java
index ab509c82e..f6c3b4dec 100644
--- a/api/src/main/java/edu/cornell/mannlib/vitro/webapp/dao/jena/RDFServiceGraph.java
+++ b/api/src/main/java/edu/cornell/mannlib/vitro/webapp/dao/jena/RDFServiceGraph.java
@@ -12,10 +12,10 @@ import java.util.function.Supplier;
 import org.apache.commons.lang3.StringUtils;
 import org.apache.commons.logging.Log;
 import org.apache.commons.logging.LogFactory;
-
 import org.apache.jena.graph.Capabilities;
 import org.apache.jena.graph.Graph;
 import org.apache.jena.graph.GraphEventManager;
+import org.apache.jena.graph.GraphListener;
 import org.apache.jena.graph.GraphStatisticsHandler;
 import org.apache.jena.graph.Node;
 import org.apache.jena.graph.TransactionHandler;
@@ -23,7 +23,6 @@ import org.apache.jena.graph.Triple;
 import org.apache.jena.graph.impl.GraphWithPerform;
 import org.apache.jena.graph.impl.SimpleEventManager;
 import org.apache.jena.query.QuerySolution;
-import org.apache.jena.rdf.listeners.StatementListener;
 import org.apache.jena.rdf.model.Model;
 import org.apache.jena.rdf.model.ModelFactory;
 import org.apache.jena.rdf.model.StmtIterator;
@@ -409,7 +408,18 @@ public class RDFServiceGraph implements GraphWithPerform {
     @Override
     public GraphEventManager getEventManager() {
         if (eventManager == null) {
-            eventManager = new SimpleEventManager(this);
+            eventManager = new SimpleEventManager() {                
+                @Override
+                public void notifyEvent(Graph g, Object event) {
+                    ChangeSet changeSet = rdfService.manufactureChangeSet();
+                    changeSet.addPreChangeEvent(event);
+                    try {
+                        rdfService.changeSetUpdate(changeSet);
+                    } catch (RDFServiceException e) {
+                        throw new RuntimeException(e);
+                    }   
+                }                
+            };
         }
         return eventManager;
     }
@@ -595,21 +605,7 @@ public class RDFServiceGraph implements GraphWithPerform {
     }
 
     public static Model createRDFServiceModel(final RDFServiceGraph g) {
-        Model m = VitroModelFactory.createModelForGraph(g);
-        m.register(new StatementListener() {
-            @Override
-            public void notifyEvent(Model m, Object event) {
-                ChangeSet changeSet = g.getRDFService().manufactureChangeSet();
-                changeSet.addPreChangeEvent(event);
-                try {
-                    g.getRDFService().changeSetUpdate(changeSet);
-                } catch (RDFServiceException e) {
-                    throw new RuntimeException(e);
-                }
-            }
-
-        });
-        return m;
+        return VitroModelFactory.createModelForGraph(g);
     }
 
 	@Override
diff --git a/api/src/test/java/edu/cornell/mannlib/vitro/webapp/dao/jena/RDFServiceGraphTest.java b/api/src/test/java/edu/cornell/mannlib/vitro/webapp/dao/jena/RDFServiceGraphTest.java
new file mode 100644
index 000000000..e5c8a65fa
--- /dev/null
+++ b/api/src/test/java/edu/cornell/mannlib/vitro/webapp/dao/jena/RDFServiceGraphTest.java
@@ -0,0 +1,62 @@
+package edu.cornell.mannlib.vitro.webapp.dao.jena;
+
+import static org.junit.Assert.assertEquals;
+
+import org.apache.jena.rdf.model.Model;
+import org.apache.jena.rdf.model.ModelFactory;
+import org.junit.Test;
+
+import edu.cornell.mannlib.vitro.testing.AbstractTestClass;
+import edu.cornell.mannlib.vitro.webapp.rdfservice.ChangeListener;
+import edu.cornell.mannlib.vitro.webapp.rdfservice.ModelChange;
+import edu.cornell.mannlib.vitro.webapp.rdfservice.RDFService;
+import edu.cornell.mannlib.vitro.webapp.rdfservice.RDFServiceException;
+import edu.cornell.mannlib.vitro.webapp.rdfservice.impl.jena.model.RDFServiceModel;
+
+
+public class RDFServiceGraphTest extends AbstractTestClass {
+
+    @Test
+    /**
+     * Test that creating a new model with the same underlying RDFServiceGraph
+     * does not result in a new listener registered on that graph.  No matter
+     * how many models have been created using a given RDFServiceGraph, an event
+     * sent to the last-created model should be heard only once by the 
+     * RDFService.
+     * @throws RDFServiceException
+     */
+    public void testEventListening() throws RDFServiceException {
+        Model m = ModelFactory.createDefaultModel();
+        RDFService rdfService = new RDFServiceModel(m);
+        EventsCounter counter = new EventsCounter();
+        rdfService.registerListener(counter);
+        RDFServiceGraph g = new RDFServiceGraph(rdfService);
+        Model model = null;
+        for (int i = 0; i < 100; i++) {
+            model = RDFServiceGraph.createRDFServiceModel(g);
+        }
+        model.notifyEvent("event");
+        assertEquals(1, counter.getCount());
+    }
+    
+    private class EventsCounter implements ChangeListener {
+
+        private int count = 0;
+        
+        public int getCount() {
+            return count;
+        }
+        
+        @Override
+        public void notifyModelChange(ModelChange modelChange) {
+            // TODO Auto-generated method stub            
+        }
+
+        @Override
+        public void notifyEvent(String graphURI, Object event) {
+            count++;
+        }
+        
+    }
+    
+}