Get Topology and listener setup

src/main/java/org/geant/AppComponent.java

@@ -18,7 +18,13 @@ package org.geant;
 import org.apache.felix.scr.annotations.Activate;
 import org.apache.felix.scr.annotations.Component;
 import org.apache.felix.scr.annotations.Deactivate;
+import org.apache.felix.scr.annotations.Reference;
+import org.apache.felix.scr.annotations.ReferenceCardinality;
 import org.apache.felix.scr.annotations.Service;
+import org.onosproject.net.topology.Topology;
+import org.onosproject.net.topology.TopologyEvent;
+import org.onosproject.net.topology.TopologyListener;
+import org.onosproject.net.topology.TopologyService;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
@@ -30,9 +36,16 @@ public class AppComponent {
 
     private final Logger log = LoggerFactory.getLogger(getClass());
 
+    @Reference(cardinality = ReferenceCardinality.MANDATORY_UNARY)
+    protected TopologyService topologyService;
+
+    private TopologyProccess processor = new TopologyProccess();
+
     @Activate
     protected void activate() {
         log.info("Started");
+        topologyService.addListener(processor);
+
     }
 
     @Deactivate
@@ -40,4 +53,18 @@ public class AppComponent {
         log.info("Stopped");
     }
 
+    private class TopologyProccess implements TopologyListener {
+
+        private void printTopology() {
+            Topology topo = topologyService.currentTopology();
+            log.info("Number of devices {}", topo.deviceCount());
+            log.info("Number of links {}", topo.linkCount());
+        }
+
+        @Override
+        public void event(TopologyEvent event) {
+            printTopology();
+
+        }
+    }
 }