GUI -- Huge Refactoring of server-side message handlers (Part Two).

--- Well, it compiles, and seems to work, with the cursory testing I've done...

Change-Id: I0e59657c134e109850e4770766083370dfd9fdc2

@@ -27,10 +27,11 @@ import org.apache.felix.scr.annotations.ReferenceCardinality;
 import org.apache.felix.scr.annotations.Service;
 import org.onlab.osgi.ServiceDirectory;
 import org.onosproject.intentperf.IntentPerfCollector.Sample;
+import org.onosproject.ui.RequestHandler;
 import org.onosproject.ui.UiConnection;
 import org.onosproject.ui.UiExtension;
 import org.onosproject.ui.UiExtensionService;
-import org.onosproject.ui.UiMessageHandler;
+import org.onosproject.ui.UiMessageHandlerTwo;
 import org.onosproject.ui.UiView;
 
 import java.util.Collection;
@@ -48,14 +49,20 @@ import static org.onosproject.ui.UiView.Category.OTHER;
 @Service(value = IntentPerfUi.class)
 public class IntentPerfUi {
 
+    private static final String INTENT_PERF_START = "intentPerfStart";
+    private static final String INTENT_PERF_STOP = "intentPerfStop";
+
     @Reference(cardinality = ReferenceCardinality.MANDATORY_UNARY)
     protected UiExtensionService uiExtensionService;
 
     private final Set<StreamingControl> handlers = synchronizedSet(new HashSet<>());
 
-    private List<UiView> views = ImmutableList.of(new UiView(OTHER, "intentPerf", "Intent Performance"));
-    private UiExtension uiExtension = new UiExtension(views, this::newHandlers,
-                                                      getClass().getClassLoader());
+    private List<UiView> views = ImmutableList.of(
+            new UiView(OTHER, "intentPerf", "Intent Performance")
+    );
+
+    private UiExtension uiExtension =
+            new UiExtension(views, this::newHandlers, getClass().getClassLoader());
 
     private IntentPerfCollector collector;
 
@@ -90,25 +97,22 @@ public class IntentPerfUi {
     }
 
     // Creates and returns session specific message handler.
-    private Collection<UiMessageHandler> newHandlers() {
+    private Collection<UiMessageHandlerTwo> newHandlers() {
         return ImmutableList.of(new StreamingControl());
     }
 
+
     // UI Message handlers for turning on/off reporting to a session.
-    private class StreamingControl extends UiMessageHandler {
+    private class StreamingControl extends UiMessageHandlerTwo {
 
         private boolean streamingEnabled = false;
 
-        protected StreamingControl() {
-            super(ImmutableSet.of("intentPerfStart", "intentPerfStop"));
-        }
-
         @Override
-        public void process(ObjectNode message) {
-            streamingEnabled = message.path("event").asText("unknown").equals("intentPerfStart");
-            if (streamingEnabled) {
-                sendInitData();
-            }
+        protected Collection<RequestHandler> getHandlers() {
+            return ImmutableSet.of(
+                    new IntentPerfStart(),
+                    new IntentPerfStop()
+            );
         }
 
         @Override
@@ -129,17 +133,6 @@ public class IntentPerfUi {
             }
         }
 
-        private void sendInitData() {
-            ObjectNode rootNode = mapper.createObjectNode();
-            ArrayNode an = mapper.createArrayNode();
-            ArrayNode sn = mapper.createArrayNode();
-            rootNode.set("headers", an);
-            rootNode.set("samples", sn);
-
-            collector.getSampleHeaders().forEach(an::add);
-            collector.getSamples().forEach(s -> sn.add(sampleNode(s)));
-            connection().sendMessage("intentPerfInit", 0, rootNode);
-        }
 
         private ObjectNode sampleNode(Sample sample) {
             ObjectNode sampleNode = mapper.createObjectNode();
@@ -153,6 +146,47 @@ public class IntentPerfUi {
             return sampleNode;
         }
 
+        // ======================================================================
+
+        private final class IntentPerfStart extends RequestHandler {
+
+            private IntentPerfStart() {
+                super(INTENT_PERF_START);
+            }
+
+            @Override
+            public void process(long sid, ObjectNode payload) {
+                streamingEnabled = true;
+                sendInitData();
+            }
+
+            private void sendInitData() {
+                ObjectNode rootNode = MAPPER.createObjectNode();
+                ArrayNode an = MAPPER.createArrayNode();
+                ArrayNode sn = MAPPER.createArrayNode();
+                rootNode.set("headers", an);
+                rootNode.set("samples", sn);
+
+                collector.getSampleHeaders().forEach(an::add);
+                collector.getSamples().forEach(s -> sn.add(sampleNode(s)));
+                sendMessage("intentPerfInit", 0, rootNode);
+            }
+        }
+
+        // ======================================================================
+
+        private final class IntentPerfStop extends RequestHandler {
+
+            private IntentPerfStop() {
+                super(INTENT_PERF_STOP);
+            }
+
+            @Override
+            public void process(long sid, ObjectNode payload) {
+                streamingEnabled = false;
+            }
+        }
+
     }
 
 }

@@ -61,6 +61,17 @@ public final class JsonUtils {
     }
 
     /**
+     * Returns the sequence identifier from the specified event, or 0 (zero)
+     * if the "sid" property does not exist.
+     *
+     * @param event message event
+     * @return extracted sequence identifier
+     */
+    public static long sid(ObjectNode event) {
+        return number(event, "sid");
+    }
+
+    /**
      * Returns the payload from the specified event.
      *
      * @param event message event
@@ -95,7 +106,7 @@ public final class JsonUtils {
     /**
      * Returns the specified node property as a string, with a default fallback.
      *
-     * @param node         message event
+     * @param node         object node
      * @param name         property name
      * @param defaultValue fallback value if property is absent
      * @return property as a string
@@ -104,4 +115,15 @@ public final class JsonUtils {
         return node.path(name).asText(defaultValue);
     }
 
+    /**
+     * Returns the specified node property as an object node.
+     *
+     * @param node object node
+     * @param name property name
+     * @return property as a node
+     */
+    public static ObjectNode node(ObjectNode node, String name) {
+        return (ObjectNode) node.path(name);
+    }
+
 }

+/*
+ * Copyright 2015 Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.onosproject.ui;
+
+import com.fasterxml.jackson.databind.ObjectMapper;
+import com.fasterxml.jackson.databind.node.ObjectNode;
+
+/**
+ * Abstraction of an entity that handles a specific request from the
+ * user interface client.
+ *
+ * @see UiMessageHandlerTwo
+ */
+public abstract class RequestHandler {
+
+    protected static final ObjectMapper MAPPER = new ObjectMapper();
+
+    private final String eventType;
+    private UiMessageHandlerTwo parent;
+
+
+    public RequestHandler(String eventType) {
+        this.eventType = eventType;
+    }
+
+    // package private
+    void setParent(UiMessageHandlerTwo parent) {
+        this.parent = parent;
+    }
+
+    /**
+     * Returns the event type that this handler handles.
+     *
+     * @return event type
+     */
+    public String eventType() {
+        return eventType;
+    }
+
+    /**
+     * Processes the incoming message payload from the client.
+     *
+     * @param sid message sequence identifier
+     * @param payload request message payload
+     */
+    public abstract void process(long sid, ObjectNode payload);
+
+
+
+    // ===================================================================
+    // === Convenience methods...
+
+    /**
+     * Returns implementation of the specified service class.
+     *
+     * @param serviceClass service class
+     * @param <T>          type of service
+     * @return implementation class
+     * @throws org.onlab.osgi.ServiceNotFoundException if no implementation found
+     */
+    protected <T> T get(Class<T> serviceClass) {
+        return parent.directory().get(serviceClass);
+    }
+
+    /**
+     * Sends a message back to the client.
+     *
+     * @param eventType message event type
+     * @param sid       message sequence identifier
+     * @param payload   message payload
+     */
+    protected void sendMessage(String eventType, long sid, ObjectNode payload) {
+        parent.connection().sendMessage(eventType, sid, payload);
+    }
+
+    /**
+     * Sends a message back to the client.
+     * Here, the message is preformatted; the assumption is it has its
+     * eventType, sid and payload attributes already filled in.
+     *
+     * @param message the message to send
+     */
+    protected void sendMessage(ObjectNode message) {
+        parent.connection().sendMessage(message);
+    }
+
+    /**
+     * Allows one request handler to pass the event on to another for
+     * further processing.
+     * Note that the message handlers must be defined in the same parent.
+     *
+     * @param eventType event type
+     * @param sid       sequence identifier
+     * @param payload   message payload
+     */
+    protected void chain(String eventType, long sid, ObjectNode payload) {
+        parent.exec(eventType, sid, payload);
+    }
+
+    // ===================================================================
+
+
+    // FIXME : Javadocs
+    protected String string(ObjectNode node, String key) {
+        return JsonUtils.string(node, key);
+    }
+
+    protected String string(ObjectNode node, String key, String defValue) {
+        return JsonUtils.string(node, key, defValue);
+    }
+
+}

@@ -40,6 +40,7 @@ import static com.google.common.base.Preconditions.checkNotNull;
  * }
  * </pre>
  */
+@Deprecated
 public abstract class UiMessageHandler {
 
     private final Set<String> messageTypes;

@@ -28,6 +28,6 @@ public interface UiMessageHandlerFactory {
      *
      * @return collection of new handlers
      */
-    Collection<UiMessageHandler> newHandlers();
+    Collection<UiMessageHandlerTwo> newHandlers();
 
 }

+/*
+ * Copyright 2015 Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.onosproject.ui;
+
+import com.fasterxml.jackson.databind.ObjectMapper;
+import com.fasterxml.jackson.databind.node.ObjectNode;
+import org.onlab.osgi.ServiceDirectory;
+
+import java.util.Collection;
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.Map;
+import java.util.Set;
+
+import static com.google.common.base.Preconditions.checkArgument;
+import static com.google.common.base.Preconditions.checkNotNull;
+
+/**
+ * Abstraction of an entity capable of processing a JSON message from the user
+ * interface client.
+ * <p>
+ * The message is a JSON object with the following structure:
+ * </p>
+ * <pre>
+ * {
+ *     "type": "<em>event-type</em>",
+ *     "sid": "<em>sequence-number</em>",
+ *     "payload": {
+ *         <em>arbitrary JSON object structure</em>
+ *     }
+ * }
+ * </pre>
+ */
+public abstract class UiMessageHandlerTwo {
+
+    private final Map<String, RequestHandler> handlerMap = new HashMap<>();
+
+    private UiConnection connection;
+    private ServiceDirectory directory;
+
+    /**
+     * Mapper for creating ObjectNodes and ArrayNodes etc.
+     */
+    protected final ObjectMapper mapper = new ObjectMapper();
+
+    /**
+     * Binds the handlers returned from {@link #getHandlers()} to this
+     * instance.
+     */
+    void bindHandlers() {
+        Collection<RequestHandler> handlers = getHandlers();
+        checkNotNull(handlers, "Handlers cannot be null");
+        checkArgument(!handlers.isEmpty(), "Handlers cannot be empty");
+
+        for (RequestHandler h : handlers) {
+            h.setParent(this);
+            handlerMap.put(h.eventType(), h);
+        }
+    }
+
+    /**
+     * Subclasses must return the collection of handlers for the
+     * message types they handle.
+     *
+     * @return the message handler instances
+     */
+    protected abstract Collection<RequestHandler> getHandlers();
+
+    /**
+     * Returns the set of message types which this handler is capable of
+     * processing.
+     *
+     * @return set of message types
+     */
+    public Set<String> messageTypes() {
+        return Collections.unmodifiableSet(handlerMap.keySet());
+    }
+
+    /**
+     * Processes a JSON message from the user interface client.
+     *
+     * @param message JSON message
+     */
+    public void process(ObjectNode message) {
+        String type = JsonUtils.eventType(message);
+        long sid = JsonUtils.sid(message);
+        ObjectNode payload = JsonUtils.payload(message);
+        exec(type, sid, payload);
+    }
+
+    /**
+     * Finds the appropriate handler and executes the process method.
+     *
+     * @param eventType event type
+     * @param sid       sequence identifier
+     * @param payload   message payload
+     */
+    void exec(String eventType, long sid, ObjectNode payload) {
+        RequestHandler handler = handlerMap.get(eventType);
+        if (handler != null) {
+            handler.process(sid, payload);
+        }
+    }
+
+    /**
+     * Initializes the handler with the user interface connection and
+     * service directory context.
+     *
+     * @param connection user interface connection
+     * @param directory  service directory
+     */
+    public void init(UiConnection connection, ServiceDirectory directory) {
+        this.connection = connection;
+        this.directory = directory;
+        bindHandlers();
+    }
+
+    /**
+     * Destroys the message handler context.
+     */
+    public void destroy() {
+        this.connection = null;
+        this.directory = null;
+    }
+
+    /**
+     * Returns the user interface connection with which this handler was primed.
+     *
+     * @return user interface connection
+     */
+    public UiConnection connection() {
+        return connection;
+    }
+
+    /**
+     * Returns the user interface connection with which this handler was primed.
+     *
+     * @return user interface connection
+     */
+    public ServiceDirectory directory() {
+        return directory;
+    }
+
+    /**
+     * Returns implementation of the specified service class.
+     *
+     * @param serviceClass service class
+     * @param <T>          type of service
+     * @return implementation class
+     * @throws org.onlab.osgi.ServiceNotFoundException if no implementation found
+     */
+    protected <T> T get(Class<T> serviceClass) {
+        return directory.get(serviceClass);
+    }
+
+}

@@ -73,4 +73,19 @@ public abstract class AbstractTableRow implements TableRow {
     protected void add(String id, Object value) {
         cells.put(id, value.toString());
     }
+
+    /**
+     * Concatenates an arbitrary number of objects, using their
+     * toString() methods.
+     *
+     * @param items the items to concatenate
+     * @return a concatenated string
+     */
+    protected static String concat(Object... items) {
+        StringBuilder sb = new StringBuilder();
+        for (Object o : items) {
+            sb.append(o);
+        }
+        return sb.toString();
+    }
 }

@@ -22,13 +22,15 @@ import org.onosproject.app.ApplicationService;
 import org.onosproject.app.ApplicationState;
 import org.onosproject.core.Application;
 import org.onosproject.core.ApplicationId;
-import org.onosproject.ui.UiMessageHandler;
+import org.onosproject.ui.RequestHandler;
+import org.onosproject.ui.UiMessageHandlerTwo;
 import org.onosproject.ui.table.AbstractTableRow;
 import org.onosproject.ui.table.RowComparator;
 import org.onosproject.ui.table.TableRow;
 import org.onosproject.ui.table.TableUtils;
 
 import java.util.Arrays;
+import java.util.Collection;
 import java.util.List;
 import java.util.stream.Collectors;
 
@@ -37,40 +39,57 @@ import static org.onosproject.app.ApplicationState.ACTIVE;
 /**
  * Message handler for application view related messages.
  */
-public class ApplicationViewMessageHandler extends UiMessageHandler {
+public class ApplicationViewMessageHandler extends UiMessageHandlerTwo {
 
-    /**
-     * Creates a new message handler for the application messages.
-     */
-    protected ApplicationViewMessageHandler() {
-        super(ImmutableSet.of("appDataRequest", "appManagementRequest"));
-    }
+    private static final String APP_DATA_REQ = "appDataRequest";
+    private static final String APP_MGMT_REQ = "appManagementRequest";
 
     @Override
-    public void process(ObjectNode message) {
-        String type = eventType(message);
-        if (type.equals("appDataRequest")) {
-            sendAppList(message);
-        } else if (type.equals("appManagementRequest")) {
-            processManagementCommand(message);
+    protected Collection<RequestHandler> getHandlers() {
+        return ImmutableSet.of(
+                new AppDataRequest(),
+                new AppMgmtRequest()
+        );
     }
+
+    // ======================================================================
+
+    private final class AppDataRequest extends RequestHandler {
+
+        private AppDataRequest() {
+            super(APP_DATA_REQ);
         }
 
-    private void sendAppList(ObjectNode message) {
-        ObjectNode payload = payload(message);
+        @Override
+        public void process(long sid, ObjectNode payload) {
             RowComparator rc = TableUtils.createRowComparator(payload);
 
             ApplicationService service = get(ApplicationService.class);
             TableRow[] rows = generateTableRows(service);
             Arrays.sort(rows, rc);
-        ObjectNode rootNode = mapper.createObjectNode();
+            ObjectNode rootNode = MAPPER.createObjectNode();
             rootNode.set("apps", TableUtils.generateArrayNode(rows));
 
-        connection().sendMessage("appDataResponse", 0, rootNode);
+            sendMessage("appDataResponse", 0, rootNode);
         }
 
-    private void processManagementCommand(ObjectNode message) {
-        ObjectNode payload = payload(message);
+        private TableRow[] generateTableRows(ApplicationService service) {
+            List<TableRow> list = service.getApplications().stream()
+                    .map(application -> new ApplicationTableRow(service, application))
+                    .collect(Collectors.toList());
+            return list.toArray(new TableRow[list.size()]);
+        }
+    }
+    // ======================================================================
+
+    private final class AppMgmtRequest extends RequestHandler {
+
+        private AppMgmtRequest() {
+            super(APP_MGMT_REQ);
+        }
+
+        @Override
+        public void process(long sid, ObjectNode payload) {
             String action = string(payload, "action");
             String name = string(payload, "name");
             if (action != null && name != null) {
@@ -83,16 +102,11 @@ public class ApplicationViewMessageHandler extends UiMessageHandler {
                 } else if (action.equals("uninstall")) {
                     service.uninstall(appId);
                 }
-            sendAppList(message);
+                chain(APP_DATA_REQ, sid, payload);
             }
         }
-
-    private TableRow[] generateTableRows(ApplicationService service) {
-        List<TableRow> list = service.getApplications().stream()
-                .map(application -> new ApplicationTableRow(service, application))
-                .collect(Collectors.toList());
-        return list.toArray(new TableRow[list.size()]);
     }
+    // ======================================================================
 
     /**
      * TableRow implementation for

@@ -23,57 +23,61 @@ import org.joda.time.format.DateTimeFormat;
 import org.onosproject.cluster.ClusterService;
 import org.onosproject.cluster.ControllerNode;
 import org.onosproject.cluster.NodeId;
-import org.onosproject.ui.UiMessageHandler;
+import org.onosproject.ui.RequestHandler;
+import org.onosproject.ui.UiMessageHandlerTwo;
 import org.onosproject.ui.table.AbstractTableRow;
 import org.onosproject.ui.table.RowComparator;
 import org.onosproject.ui.table.TableRow;
 import org.onosproject.ui.table.TableUtils;
 
-import java.util.ArrayList;
 import java.util.Arrays;
+import java.util.Collection;
 import java.util.List;
+import java.util.stream.Collectors;
 
 
 /**
  * Message handler for cluster view related messages.
  */
-public class ClusterViewMessageHandler extends UiMessageHandler {
+public class ClusterViewMessageHandler extends UiMessageHandlerTwo {
 
-    /**
-     * Creates a new message handler for the cluster messages.
-     */
-    protected ClusterViewMessageHandler() {
-        super(ImmutableSet.of("clusterDataRequest"));
-    }
+    private static final String CLUSTER_DATA_REQ = "clusterDataRequest";
 
     @Override
-    public void process(ObjectNode message) {
-        String type = eventType(message);
-        if (type.equals("clusterDataRequest")) {
-            sendClusterList(message);
+    protected Collection<RequestHandler> getHandlers() {
+        return ImmutableSet.of(new ClusterDataRequest());
     }
+
+    // ======================================================================
+
+    private final class ClusterDataRequest extends RequestHandler {
+
+        private ClusterDataRequest() {
+            super(CLUSTER_DATA_REQ);
         }
 
-    private void sendClusterList(ObjectNode message) {
-        ObjectNode payload = payload(message);
+        @Override
+        public void process(long sid, ObjectNode payload) {
             RowComparator rc = TableUtils.createRowComparator(payload);
 
             ClusterService service = get(ClusterService.class);
             TableRow[] rows = generateTableRows(service);
             Arrays.sort(rows, rc);
-        ObjectNode rootNode = mapper.createObjectNode();
+            ObjectNode rootNode = MAPPER.createObjectNode();
             rootNode.set("clusters", TableUtils.generateArrayNode(rows));
 
-        connection().sendMessage("clusterDataResponse", 0, rootNode);
+            sendMessage("clusterDataResponse", 0, rootNode);
         }
 
         private TableRow[] generateTableRows(ClusterService service) {
-        List<TableRow> list = new ArrayList<>();
-        for (ControllerNode node : service.getNodes()) {
-            list.add(new ControllerNodeTableRow(service, node));
-        }
+            List<TableRow> list = service.getNodes().stream()
+                    .map(node -> new ControllerNodeTableRow(service, node))
+                    .collect(Collectors.toList());
             return list.toArray(new TableRow[list.size()]);
         }
+    }
+
+    // ======================================================================
 
     /**
      * TableRow implementation for {@link ControllerNode controller nodes}.

@@ -27,7 +27,8 @@ import org.onosproject.net.Link;
 import org.onosproject.net.Port;
 import org.onosproject.net.device.DeviceService;
 import org.onosproject.net.link.LinkService;
-import org.onosproject.ui.UiMessageHandler;
+import org.onosproject.ui.RequestHandler;
+import org.onosproject.ui.UiMessageHandlerTwo;
 import org.onosproject.ui.table.AbstractTableRow;
 import org.onosproject.ui.table.RowComparator;
 import org.onosproject.ui.table.TableRow;
@@ -35,6 +36,7 @@ import org.onosproject.ui.table.TableUtils;
 
 import java.util.ArrayList;
 import java.util.Arrays;
+import java.util.Collection;
 import java.util.Collections;
 import java.util.List;
 import java.util.Set;
@@ -42,7 +44,10 @@ import java.util.Set;
 /**
  * Message handler for device view related messages.
  */
-public class DeviceViewMessageHandler extends UiMessageHandler {
+public class DeviceViewMessageHandler extends UiMessageHandlerTwo {
+
+    private static final String DEV_DATA_REQ = "deviceDataRequest";
+    private static final String DEV_DETAIL_REQ = "deviceDetailRequest";
 
     private static final String ID = "id";
     private static final String TYPE = "type";
@@ -65,46 +70,62 @@ public class DeviceViewMessageHandler extends UiMessageHandler {
     private static final String NAME = "name";
 
 
-    /**
-     * Creates a new message handler for the device messages.
-     */
-    protected DeviceViewMessageHandler() {
-        super(ImmutableSet.of("deviceDataRequest", "deviceDetailsRequest"));
-    }
-
     @Override
-    public void process(ObjectNode message) {
-        String type = eventType(message);
-        if (type.equals("deviceDataRequest")) {
-            dataRequest(message);
-        } else if (type.equals("deviceDetailsRequest")) {
-            detailsRequest(message);
+    protected Collection<RequestHandler> getHandlers() {
+        return ImmutableSet.of(
+                new DataRequestHandler(),
+                new DetailRequestHandler()
+        );
     }
+
+    // ======================================================================
+
+    private final class DataRequestHandler extends RequestHandler {
+
+        private DataRequestHandler() {
+            super(DEV_DATA_REQ);
         }
 
-    private void dataRequest(ObjectNode message) {
-        ObjectNode payload = payload(message);
+        @Override
+        public void process(long sid, ObjectNode payload) {
             RowComparator rc = TableUtils.createRowComparator(payload);
 
             DeviceService service = get(DeviceService.class);
             MastershipService mastershipService = get(MastershipService.class);
             TableRow[] rows = generateTableRows(service, mastershipService);
             Arrays.sort(rows, rc);
-        ObjectNode rootNode = mapper.createObjectNode();
+            ObjectNode rootNode = MAPPER.createObjectNode();
             rootNode.set("devices", TableUtils.generateArrayNode(rows));
 
-        connection().sendMessage("deviceDataResponse", 0, rootNode);
+            sendMessage("deviceDataResponse", 0, rootNode);
         }
 
-    private void detailsRequest(ObjectNode message) {
-        ObjectNode payload = payload(message);
+        private TableRow[] generateTableRows(DeviceService service,
+                                             MastershipService mastershipService) {
+            List<TableRow> list = new ArrayList<>();
+            for (Device dev : service.getDevices()) {
+                list.add(new DeviceTableRow(service, mastershipService, dev));
+            }
+            return list.toArray(new TableRow[list.size()]);
+        }
+    }
+
+    // ======================================================================
+
+    private final class DetailRequestHandler extends RequestHandler {
+        private DetailRequestHandler() {
+            super(DEV_DETAIL_REQ);
+        }
+
+        @Override
+        public void process(long sid, ObjectNode payload) {
             String id = string(payload, "id", "of:0000000000000000");
 
             DeviceId deviceId = DeviceId.deviceId(id);
             DeviceService service = get(DeviceService.class);
             MastershipService ms = get(MastershipService.class);
             Device device = service.getDevice(deviceId);
-        ObjectNode data = mapper.createObjectNode();
+            ObjectNode data = MAPPER.createObjectNode();
 
             data.put(ID, deviceId.toString());
             data.put(TYPE, device.type().toString());
@@ -117,7 +138,7 @@ public class DeviceViewMessageHandler extends UiMessageHandler {
             data.put(MASTER_ID, ms.getMasterFor(deviceId).toString());
             data.put(PROTOCOL, device.annotations().value(PROTOCOL));
 
-        ArrayNode ports = mapper.createArrayNode();
+            ArrayNode ports = MAPPER.createArrayNode();
 
             List<Port> portList = new ArrayList<>(service.getPorts(deviceId));
             Collections.sort(portList, (p1, p2) -> {
@@ -130,22 +151,13 @@ public class DeviceViewMessageHandler extends UiMessageHandler {
             }
             data.set(PORTS, ports);
 
-        ObjectNode rootNode = mapper.createObjectNode();
+            ObjectNode rootNode = MAPPER.createObjectNode();
             rootNode.set("details", data);
-        connection().sendMessage("deviceDetailsResponse", 0, rootNode);
-    }
-
-    private TableRow[] generateTableRows(DeviceService service,
-                                         MastershipService mastershipService) {
-        List<TableRow> list = new ArrayList<>();
-        for (Device dev : service.getDevices()) {
-            list.add(new DeviceTableRow(service, mastershipService, dev));
-        }
-        return list.toArray(new TableRow[list.size()]);
+            sendMessage("deviceDetailsResponse", 0, rootNode);
         }
 
         private ObjectNode portData(Port p, DeviceId id) {
-        ObjectNode port = mapper.createObjectNode();
+            ObjectNode port = MAPPER.createObjectNode();
             LinkService ls = get(LinkService.class);
             String name = p.annotations().value(AnnotationKeys.PORT_NAME);
 
@@ -169,6 +181,9 @@ public class DeviceViewMessageHandler extends UiMessageHandler {
             return port;
         }
 
+    }
+
+
     private static String getTypeIconId(Device d) {
         return DEV_ICON_PREFIX + d.type().toString();
     }

@@ -26,7 +26,8 @@ import org.onosproject.net.flow.TrafficSelector;
 import org.onosproject.net.flow.TrafficTreatment;
 import org.onosproject.net.flow.criteria.Criterion;
 import org.onosproject.net.flow.instructions.Instruction;
-import org.onosproject.ui.UiMessageHandler;
+import org.onosproject.ui.RequestHandler;
+import org.onosproject.ui.UiMessageHandlerTwo;
 import org.onosproject.ui.table.AbstractTableRow;
 import org.onosproject.ui.table.RowComparator;
 import org.onosproject.ui.table.TableRow;
@@ -34,6 +35,7 @@ import org.onosproject.ui.table.TableUtils;
 
 import java.util.ArrayList;
 import java.util.Arrays;
+import java.util.Collection;
 import java.util.List;
 import java.util.Set;
 
@@ -41,44 +43,44 @@ import java.util.Set;
 /**
  * Message handler for flow view related messages.
  */
-public class FlowViewMessageHandler extends UiMessageHandler {
+public class FlowViewMessageHandler extends UiMessageHandlerTwo {
 
-    private static final String NO_DEV = "none";
+    private static final String FLOW_DATA_REQ = "flowDataRequest";
 
-    /**
-     * Creates a new message handler for the flow messages.
-     */
-    protected FlowViewMessageHandler() {
-        super(ImmutableSet.of("flowDataRequest"));
-    }
+    private static final String NO_DEV = "none";
 
     @Override
-    public void process(ObjectNode message) {
-        String type = eventType(message);
-        if (type.equals("flowDataRequest")) {
-            sendFlowList(message);
+    protected Collection<RequestHandler> getHandlers() {
+        return ImmutableSet.of(new FlowDataRequest());
     }
+
+    // ======================================================================
+
+    private final class FlowDataRequest extends RequestHandler {
+
+        private FlowDataRequest() {
+            super(FLOW_DATA_REQ);
         }
 
-    private void sendFlowList(ObjectNode message) {
-        ObjectNode payload = payload(message);
+        @Override
+        public void process(long sid, ObjectNode payload) {
             RowComparator rc = TableUtils.createRowComparator(payload);
             String uri = string(payload, "devId", NO_DEV);
 
             ObjectNode rootNode;
             if (uri.equals(NO_DEV)) {
-            rootNode = mapper.createObjectNode();
-            rootNode.set("flows", mapper.createArrayNode());
+                rootNode = MAPPER.createObjectNode();
+                rootNode.set("flows", MAPPER.createArrayNode());
             } else {
                 DeviceId deviceId = DeviceId.deviceId(uri);
                 FlowRuleService service = get(FlowRuleService.class);
                 TableRow[] rows = generateTableRows(service, deviceId);
                 Arrays.sort(rows, rc);
-            rootNode = mapper.createObjectNode();
+                rootNode = MAPPER.createObjectNode();
                 rootNode.set("flows", TableUtils.generateArrayNode(rows));
             }
 
-        connection().sendMessage("flowDataResponse", 0, rootNode);
+            sendMessage("flowDataResponse", 0, rootNode);
         }
 
         private TableRow[] generateTableRows(FlowRuleService service,
@@ -89,6 +91,9 @@ public class FlowViewMessageHandler extends UiMessageHandler {
             }
             return list.toArray(new TableRow[list.size()]);
         }
+    }
+
+    // ======================================================================
 
     /**
      * TableRow implementation for {@link org.onosproject.net.flow.FlowRule flows}.

@@ -21,7 +21,8 @@ import org.onosproject.net.AnnotationKeys;
 import org.onosproject.net.Host;
 import org.onosproject.net.HostLocation;
 import org.onosproject.net.host.HostService;
-import org.onosproject.ui.UiMessageHandler;
+import org.onosproject.ui.RequestHandler;
+import org.onosproject.ui.UiMessageHandlerTwo;
 import org.onosproject.ui.table.AbstractTableRow;
 import org.onosproject.ui.table.RowComparator;
 import org.onosproject.ui.table.TableRow;
@@ -29,6 +30,7 @@ import org.onosproject.ui.table.TableUtils;
 
 import java.util.ArrayList;
 import java.util.Arrays;
+import java.util.Collection;
 import java.util.List;
 
 import static com.google.common.base.Strings.isNullOrEmpty;
@@ -36,34 +38,35 @@ import static com.google.common.base.Strings.isNullOrEmpty;
 /**
  * Message handler for host view related messages.
  */
-public class HostViewMessageHandler extends UiMessageHandler {
+public class HostViewMessageHandler extends UiMessageHandlerTwo {
+
+    private static final String HOST_DATA_REQ = "hostDataRequest";
 
-    /**
-     * Creates a new message handler for the host messages.
-     */
-    protected HostViewMessageHandler() {
-        super(ImmutableSet.of("hostDataRequest"));
-    }
 
     @Override
-    public void process(ObjectNode message) {
-        String type = eventType(message);
-        if (type.equals("hostDataRequest")) {
-            sendHostList(message);
+    protected Collection<RequestHandler> getHandlers() {
+        return ImmutableSet.of(new HostDataRequest());
     }
+
+    // ======================================================================
+
+    private final class HostDataRequest extends RequestHandler {
+
+        private HostDataRequest() {
+            super(HOST_DATA_REQ);
         }
 
-    private void sendHostList(ObjectNode message) {
-        ObjectNode payload = payload(message);
+        @Override
+        public void process(long sid, ObjectNode payload) {
             RowComparator rc = TableUtils.createRowComparator(payload);
 
             HostService service = get(HostService.class);
             TableRow[] rows = generateTableRows(service);
             Arrays.sort(rows, rc);
-        ObjectNode rootNode = mapper.createObjectNode();
+            ObjectNode rootNode = MAPPER.createObjectNode();
             rootNode.set("hosts", TableUtils.generateArrayNode(rows));
 
-        connection().sendMessage("hostDataResponse", 0, rootNode);
+            sendMessage("hostDataResponse", 0, rootNode);
         }
 
         private TableRow[] generateTableRows(HostService service) {
@@ -73,6 +76,9 @@ public class HostViewMessageHandler extends UiMessageHandler {
             }
             return list.toArray(new TableRow[list.size()]);
         }
+    }
+
+    // ======================================================================
 
     /**
      * TableRow implementation for {@link Host hosts}.

@@ -31,7 +31,8 @@ import org.onosproject.net.intent.MultiPointToSinglePointIntent;
 import org.onosproject.net.intent.PathIntent;
 import org.onosproject.net.intent.PointToPointIntent;
 import org.onosproject.net.intent.SinglePointToMultiPointIntent;
-import org.onosproject.ui.UiMessageHandler;
+import org.onosproject.ui.RequestHandler;
+import org.onosproject.ui.UiMessageHandlerTwo;
 import org.onosproject.ui.table.AbstractTableRow;
 import org.onosproject.ui.table.RowComparator;
 import org.onosproject.ui.table.TableRow;
@@ -39,40 +40,42 @@ import org.onosproject.ui.table.TableUtils;
 
 import java.util.ArrayList;
 import java.util.Arrays;
+import java.util.Collection;
 import java.util.List;
 import java.util.Set;
 
 /**
  * Message handler for intent view related messages.
  */
-public class IntentViewMessageHandler extends UiMessageHandler {
+public class IntentViewMessageHandler extends UiMessageHandlerTwo {
+
+    private static final String INTENT_DATA_REQ = "intentDataRequest";
 
-    /**
-     * Creates a new message handler for the intent messages.
-     */
-    protected IntentViewMessageHandler() {
-        super(ImmutableSet.of("intentDataRequest"));
-    }
 
     @Override
-    public void process(ObjectNode message) {
-        String type = eventType(message);
-        if (type.equals("intentDataRequest")) {
-            sendIntentList(message);
+    protected Collection<RequestHandler> getHandlers() {
+        return ImmutableSet.of(new IntentDataRequest());
     }
+
+    // ======================================================================
+
+    private final class IntentDataRequest extends RequestHandler {
+
+        private IntentDataRequest() {
+            super(INTENT_DATA_REQ);
         }
 
-    private void sendIntentList(ObjectNode message) {
-        ObjectNode payload = payload(message);
+        @Override
+        public void process(long sid, ObjectNode payload) {
             RowComparator rc = TableUtils.createRowComparator(payload);
 
             IntentService service = get(IntentService.class);
             TableRow[] rows = generateTableRows(service);
             Arrays.sort(rows, rc);
-        ObjectNode rootNode = mapper.createObjectNode();
+            ObjectNode rootNode = MAPPER.createObjectNode();
             rootNode.set("intents", TableUtils.generateArrayNode(rows));
 
-        connection().sendMessage("intentDataResponse", 0, rootNode);
+            sendMessage("intentDataResponse", 0, rootNode);
         }
 
         private TableRow[] generateTableRows(IntentService service) {
@@ -82,6 +85,9 @@ public class IntentViewMessageHandler extends UiMessageHandler {
             }
             return list.toArray(new TableRow[list.size()]);
         }
+    }
+
+    // ======================================================================
 
     /**
      * TableRow implementation for {@link Intent intents}.

@@ -23,7 +23,8 @@ import org.onosproject.net.ConnectPoint;
 import org.onosproject.net.Link;
 import org.onosproject.net.LinkKey;
 import org.onosproject.net.link.LinkService;
-import org.onosproject.ui.UiMessageHandler;
+import org.onosproject.ui.RequestHandler;
+import org.onosproject.ui.UiMessageHandlerTwo;
 import org.onosproject.ui.impl.TopologyViewMessageHandlerBase.BiLink;
 import org.onosproject.ui.table.AbstractTableRow;
 import org.onosproject.ui.table.RowComparator;
@@ -32,6 +33,7 @@ import org.onosproject.ui.table.TableUtils;
 
 import java.util.ArrayList;
 import java.util.Arrays;
+import java.util.Collection;
 import java.util.List;
 import java.util.Map;
 
@@ -40,34 +42,35 @@ import static org.onosproject.ui.impl.TopologyViewMessageHandlerBase.addLink;
 /**
  * Message handler for link view related messages.
  */
-public class LinkViewMessageHandler extends UiMessageHandler {
+public class LinkViewMessageHandler extends UiMessageHandlerTwo {
+
+    private static final String LINK_DATA_REQ = "linkDataRequest";
 
-    /**
-     * Creates a new message handler for the link messages.
-     */
-    protected LinkViewMessageHandler() {
-        super(ImmutableSet.of("linkDataRequest"));
-    }
 
     @Override
-    public void process(ObjectNode message) {
-        String type = eventType(message);
-        if (type.equals("linkDataRequest")) {
-            sendLinkList(message);
+    protected Collection<RequestHandler> getHandlers() {
+        return ImmutableSet.of(new LinkDataRequest());
     }
+
+    // ======================================================================
+
+    private final class LinkDataRequest extends RequestHandler {
+
+        private LinkDataRequest() {
+            super(LINK_DATA_REQ);
         }
 
-    private void sendLinkList(ObjectNode message) {
-        ObjectNode payload = payload(message);
+        @Override
+        public void process(long sid, ObjectNode payload) {
             RowComparator rc = TableUtils.createRowComparator(payload, "one");
 
             LinkService service = get(LinkService.class);
             TableRow[] rows = generateTableRows(service);
             Arrays.sort(rows, rc);
-        ObjectNode rootNode = mapper.createObjectNode();
+            ObjectNode rootNode = MAPPER.createObjectNode();
             rootNode.set("links", TableUtils.generateArrayNode(rows));
 
-        connection().sendMessage("linkDataResponse", 0, rootNode);
+            sendMessage("linkDataResponse", 0, rootNode);
         }
 
         private TableRow[] generateTableRows(LinkService service) {
@@ -81,6 +84,9 @@ public class LinkViewMessageHandler extends UiMessageHandler {
             biLinks.values().forEach(biLink -> list.add(new LinkTableRow(biLink)));
             return list.toArray(new TableRow[list.size()]);
         }
+    }
+
+    // ======================================================================
 
     /**
      * TableRow implementation for {@link org.onosproject.net.Link links}.

@@ -63,8 +63,9 @@ import org.onosproject.net.statistic.Load;
 import org.onosproject.net.statistic.StatisticService;
 import org.onosproject.net.topology.Topology;
 import org.onosproject.net.topology.TopologyService;
+import org.onosproject.ui.JsonUtils;
 import org.onosproject.ui.UiConnection;
-import org.onosproject.ui.UiMessageHandler;
+import org.onosproject.ui.UiMessageHandlerTwo;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
@@ -100,11 +101,13 @@ import static org.onosproject.net.link.LinkEvent.Type.LINK_REMOVED;
 /**
  * Facility for creating messages bound for the topology viewer.
  */
-public abstract class TopologyViewMessageHandlerBase extends UiMessageHandler {
+public abstract class TopologyViewMessageHandlerBase extends UiMessageHandlerTwo {
 
-    protected static final Logger log = LoggerFactory.getLogger(TopologyViewMessageHandlerBase.class);
+    protected static final Logger log =
+            LoggerFactory.getLogger(TopologyViewMessageHandlerBase.class);
 
-    private static final ProviderId PID = new ProviderId("core", "org.onosproject.core", true);
+    private static final ProviderId PID =
+            new ProviderId("core", "org.onosproject.core", true);
     private static final String COMPACT = "%s/%s-%s/%s";
 
     private static final double KB = 1024;
@@ -133,15 +136,6 @@ public abstract class TopologyViewMessageHandlerBase extends UiMessageHandler {
     private static Map<String, ObjectNode> metaUi = new ConcurrentHashMap<>();
 
     /**
-     * Creates a new message handler for the specified set of message types.
-     *
-     * @param messageTypes set of message types
-     */
-    protected TopologyViewMessageHandlerBase(Set<String> messageTypes) {
-        super(messageTypes);
-    }
-
-    /**
      * Returns read-only view of the meta-ui information.
      *
      * @return map of id to meta-ui mementos
@@ -168,26 +162,6 @@ public abstract class TopologyViewMessageHandlerBase extends UiMessageHandler {
         version = ver.replace(".SNAPSHOT", "*").replaceFirst("~.*$", "");
     }
 
-    // Retrieves the payload from the specified event.
-    protected ObjectNode payload(ObjectNode event) {
-        return (ObjectNode) event.path("payload");
-    }
-
-    // Returns the specified node property as a number
-    protected long number(ObjectNode node, String name) {
-        return node.path(name).asLong();
-    }
-
-    // Returns the specified node property as a string.
-    protected String string(ObjectNode node, String name) {
-        return node.path(name).asText();
-    }
-
-    // Returns the specified node property as a string.
-    protected String string(ObjectNode node, String name, String defaultValue) {
-        return node.path(name).asText(defaultValue);
-    }
-
     // Returns the specified set of IP addresses as a string.
     private String ip(Set<IpAddress> ipAddresses) {
         Iterator<IpAddress> it = ipAddresses.iterator();
@@ -222,21 +196,11 @@ public abstract class TopologyViewMessageHandlerBase extends UiMessageHandler {
 
     // Produces a log message event bound to the client.
     private ObjectNode message(String severity, long id, String message) {
-        return envelope("message", id,
-                        mapper.createObjectNode()
+        ObjectNode payload = mapper.createObjectNode()
                 .put("severity", severity)
-                                .put("message", message));
-    }
+                .put("message", message);
 
-    // Puts the payload into an envelope and returns it.
-    protected ObjectNode envelope(String type, long sid, ObjectNode payload) {
-        ObjectNode event = mapper.createObjectNode();
-        event.put("event", type);
-        if (sid > 0) {
-            event.put("sid", sid);
-        }
-        event.set("payload", payload);
-        return event;
+        return JsonUtils.envelope("message", id, payload);
     }
 
     // Produces a set of all hosts listed in the specified JSON array.
@@ -320,7 +284,7 @@ public abstract class TopologyViewMessageHandlerBase extends UiMessageHandler {
                 ((event.type() == INSTANCE_ADDED) ? "addInstance" :
                         ((event.type() == INSTANCE_REMOVED ? "removeInstance" :
                                 "addInstance")));
-        return envelope(type, 0, payload);
+        return JsonUtils.envelope(type, 0, payload);
     }
 
     // Produces a device event message to the client.
@@ -347,7 +311,7 @@ public abstract class TopologyViewMessageHandlerBase extends UiMessageHandler {
 
         String type = (event.type() == DEVICE_ADDED) ? "addDevice" :
                 ((event.type() == DEVICE_REMOVED) ? "removeDevice" : "updateDevice");
-        return envelope(type, 0, payload);
+        return JsonUtils.envelope(type, 0, payload);
     }
 
     // Produces a link event message to the client.
@@ -364,7 +328,7 @@ public abstract class TopologyViewMessageHandlerBase extends UiMessageHandler {
                 .put("dstPort", link.dst().port().toString());
         String type = (event.type() == LINK_ADDED) ? "addLink" :
                 ((event.type() == LINK_REMOVED) ? "removeLink" : "updateLink");
-        return envelope(type, 0, payload);
+        return JsonUtils.envelope(type, 0, payload);
     }
 
     // Produces a host event message to the client.
@@ -385,7 +349,7 @@ public abstract class TopologyViewMessageHandlerBase extends UiMessageHandler {
 
         String type = (event.type() == HOST_ADDED) ? "addHost" :
                 ((event.type() == HOST_REMOVED) ? "removeHost" : "updateHost");
-        return envelope(type, 0, payload);
+        return JsonUtils.envelope(type, 0, payload);
     }
 
     // Encodes the specified host location into a JSON object.
@@ -447,15 +411,15 @@ public abstract class TopologyViewMessageHandlerBase extends UiMessageHandler {
     }
 
     // Updates meta UI information for the specified object.
-    protected void updateMetaUi(ObjectNode event) {
-        ObjectNode payload = payload(event);
-        metaUi.put(string(payload, "id"), (ObjectNode) payload.path("memento"));
+    protected void updateMetaUi(ObjectNode payload) {
+        metaUi.put(JsonUtils.string(payload, "id"),
+                   JsonUtils.node(payload, "memento"));
     }
 
     // Returns summary response.
     protected ObjectNode summmaryMessage(long sid) {
         Topology topology = topologyService.currentTopology();
-        return envelope("showSummary", sid,
+        return JsonUtils.envelope("showSummary", sid,
                         json("ONOS Summary", "node",
                              new Prop("Devices", format(topology.deviceCount())),
                              new Prop("Links", format(topology.linkCount())),
@@ -474,7 +438,7 @@ public abstract class TopologyViewMessageHandlerBase extends UiMessageHandler {
         String name = annot.value(AnnotationKeys.NAME);
         int portCount = deviceService.getPorts(deviceId).size();
         int flowCount = getFlowCount(deviceId);
-        return envelope("showDetails", sid,
+        return JsonUtils.envelope("showDetails", sid,
                         json(isNullOrEmpty(name) ? deviceId.toString() : name,
                              device.type().toString().toLowerCase(),
                              new Prop("URI", deviceId.toString()),
@@ -552,7 +516,7 @@ public abstract class TopologyViewMessageHandlerBase extends UiMessageHandler {
         String type = annot.value(AnnotationKeys.TYPE);
         String name = annot.value(AnnotationKeys.NAME);
         String vlan = host.vlan().toString();
-        return envelope("showDetails", sid,
+        return JsonUtils.envelope("showDetails", sid,
                         json(isNullOrEmpty(name) ? hostId.toString() : name,
                              isNullOrEmpty(type) ? "endstation" : type,
                              new Prop("MAC", host.mac().toString()),
@@ -565,7 +529,7 @@ public abstract class TopologyViewMessageHandlerBase extends UiMessageHandler {
 
 
     // Produces JSON message to trigger traffic overview visualization
-    protected ObjectNode trafficSummaryMessage(long sid) {
+    protected ObjectNode trafficSummaryMessage() {
         ObjectNode payload = mapper.createObjectNode();
         ArrayNode paths = mapper.createArrayNode();
         payload.set("paths", paths);
@@ -603,7 +567,7 @@ public abstract class TopologyViewMessageHandlerBase extends UiMessageHandler {
                 }
             }
         }
-        return envelope("showTraffic", sid, payload);
+        return JsonUtils.envelope("showTraffic", 0, payload);
     }
 
     private Collection<BiLink> consolidateLinks(Iterable<Link> links) {
@@ -615,7 +579,7 @@ public abstract class TopologyViewMessageHandlerBase extends UiMessageHandler {
     }
 
     // Produces JSON message to trigger flow overview visualization
-    protected ObjectNode flowSummaryMessage(long sid, Set<Device> devices) {
+    protected ObjectNode flowSummaryMessage(Set<Device> devices) {
         ObjectNode payload = mapper.createObjectNode();
         ArrayNode paths = mapper.createArrayNode();
         payload.set("paths", paths);
@@ -626,7 +590,7 @@ public abstract class TopologyViewMessageHandlerBase extends UiMessageHandler {
                 addLinkFlows(link, paths, counts.get(link));
             }
         }
-        return envelope("showTraffic", sid, payload);
+        return JsonUtils.envelope("showTraffic", 0, payload);
     }
 
     private void addLinkFlows(Link link, ArrayNode paths, Integer count) {
@@ -644,7 +608,7 @@ public abstract class TopologyViewMessageHandlerBase extends UiMessageHandler {
 
 
     // Produces JSON message to trigger traffic visualization
-    protected ObjectNode trafficMessage(long sid, TrafficClass... trafficClasses) {
+    protected ObjectNode trafficMessage(TrafficClass... trafficClasses) {
         ObjectNode payload = mapper.createObjectNode();
         ArrayNode paths = mapper.createArrayNode();
         payload.set("paths", paths);
@@ -670,7 +634,7 @@ public abstract class TopologyViewMessageHandlerBase extends UiMessageHandler {
             ((ArrayNode) pathNode.path("labels")).add(hasTraffic ? formatBytes(biLink.bytes) : "");
         }
 
-        return envelope("showTraffic", sid, payload);
+        return JsonUtils.envelope("showTraffic", 0, payload);
     }
 
     // Classifies the link traffic according to the specified classes.

@@ -24,8 +24,8 @@ import org.onosproject.cluster.ClusterService;
 import org.onosproject.cluster.ControllerNode;
 import org.onosproject.ui.UiConnection;
 import org.onosproject.ui.UiExtensionService;
-import org.onosproject.ui.UiMessageHandler;
 import org.onosproject.ui.UiMessageHandlerFactory;
+import org.onosproject.ui.UiMessageHandlerTwo;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
@@ -56,7 +56,7 @@ public class UiWebSocket
 
     private long lastActive = System.currentTimeMillis();
 
-    private Map<String, UiMessageHandler> handlers;
+    private Map<String, UiMessageHandlerTwo> handlers;
 
     /**
      * Creates a new web-socket for serving data to GUI.
@@ -123,7 +123,7 @@ public class UiWebSocket
         try {
             ObjectNode message = (ObjectNode) mapper.reader().readTree(data);
             String type = message.path("event").asText("unknown");
-            UiMessageHandler handler = handlers.get(type);
+            UiMessageHandlerTwo handler = handlers.get(type);
             if (handler != null) {
                 handler.process(message);
             } else {