Make constraint objects serializable by Kryo

Change-Id: I15e5a14b16fc1ab0416570fec176f18b713727a0

@@ -41,6 +41,12 @@ public class AnnotationConstraint extends BooleanConstraint {
         this.threshold = threshold;
     }
 
+    // Constructor for serialization
+    private AnnotationConstraint() {
+        this.key = "";
+        this.threshold = 0;
+    }
+
     /**
      * Returns the key of link annotation this constraint designates.
      * @return key of link annotation

@@ -42,6 +42,11 @@ public class LatencyConstraint implements Constraint {
         this.latency = latency;
     }
 
+    // Constructor for serialization
+    private LatencyConstraint() {
+        this.latency = Duration.ZERO;
+    }
+
     public Duration latency() {
         return latency;
     }

@@ -21,6 +21,7 @@ import org.onlab.onos.net.DeviceId;
 import org.onlab.onos.net.Link;
 import org.onlab.onos.net.resource.LinkResourceService;
 
+import java.util.Collections;
 import java.util.Objects;
 import java.util.Set;
 
@@ -39,6 +40,11 @@ public class ObstacleConstraint extends BooleanConstraint {
         this.obstacles = ImmutableSet.copyOf(obstacles);
     }
 
+    // Constructor for serialization
+    private ObstacleConstraint() {
+        this.obstacles = Collections.emptySet();
+    }
+
     @Override
     public boolean isValid(Link link, LinkResourceService resourceService) {
         DeviceId src = link.src().deviceId();

@@ -23,6 +23,7 @@ import org.onlab.onos.net.Path;
 import org.onlab.onos.net.intent.Constraint;
 import org.onlab.onos.net.resource.LinkResourceService;
 
+import java.util.Collections;
 import java.util.LinkedList;
 import java.util.List;
 import java.util.Objects;
@@ -48,6 +49,11 @@ public class WaypointConstraint implements Constraint {
         this.waypoints = ImmutableList.copyOf(waypoints);
     }
 
+    // Constructor for serialization
+    private WaypointConstraint() {
+        this.waypoints = Collections.emptyList();
+    }
+
     public List<DeviceId> waypoints() {
         return waypoints;
     }

@@ -75,10 +75,14 @@ import org.onlab.onos.net.intent.OpticalConnectivityIntent;
 import org.onlab.onos.net.intent.OpticalPathIntent;
 import org.onlab.onos.net.intent.PathIntent;
 import org.onlab.onos.net.intent.PointToPointIntent;
+import org.onlab.onos.net.intent.constraint.AnnotationConstraint;
 import org.onlab.onos.net.intent.constraint.BandwidthConstraint;
 import org.onlab.onos.net.intent.constraint.BooleanConstraint;
 import org.onlab.onos.net.intent.constraint.LambdaConstraint;
+import org.onlab.onos.net.intent.constraint.LatencyConstraint;
 import org.onlab.onos.net.intent.constraint.LinkTypeConstraint;
+import org.onlab.onos.net.intent.constraint.ObstacleConstraint;
+import org.onlab.onos.net.intent.constraint.WaypointConstraint;
 import org.onlab.onos.net.link.DefaultLinkDescription;
 import org.onlab.onos.net.packet.DefaultOutboundPacket;
 import org.onlab.onos.net.provider.ProviderId;
@@ -208,9 +212,14 @@ public final class KryoNamespaces {
                     LinkResourceRequest.class,
                     Lambda.class,
                     Bandwidth.class,
+                    // Constraints
                     LambdaConstraint.class,
                     BandwidthConstraint.class,
                     LinkTypeConstraint.class,
+                    LatencyConstraint.class,
+                    WaypointConstraint.class,
+                    ObstacleConstraint.class,
+                    AnnotationConstraint.class,
                     BooleanConstraint.class
                     )
             .register(DefaultApplicationId.class, new DefaultApplicationIdSerializer())