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
diff --git a/core/api/src/main/java/org/onosproject/ui/JsonUtils.java b/core/api/src/main/java/org/onosproject/ui/JsonUtils.java
index 152fc9b..db753e2 100644
--- a/core/api/src/main/java/org/onosproject/ui/JsonUtils.java
+++ b/core/api/src/main/java/org/onosproject/ui/JsonUtils.java
@@ -61,6 +61,17 @@
     }
 
     /**
+     * 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 @@
     /**
      * 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 @@
         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);
+    }
+
 }
diff --git a/core/api/src/main/java/org/onosproject/ui/RequestHandler.java b/core/api/src/main/java/org/onosproject/ui/RequestHandler.java
new file mode 100644
index 0000000..7231dcf
--- /dev/null
+++ b/core/api/src/main/java/org/onosproject/ui/RequestHandler.java
@@ -0,0 +1,125 @@
+/*
+ * 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);
+    }
+
+}
diff --git a/core/api/src/main/java/org/onosproject/ui/UiMessageHandler.java b/core/api/src/main/java/org/onosproject/ui/UiMessageHandler.java
index 0482162..00b3595 100644
--- a/core/api/src/main/java/org/onosproject/ui/UiMessageHandler.java
+++ b/core/api/src/main/java/org/onosproject/ui/UiMessageHandler.java
@@ -40,6 +40,7 @@
  * }
  * </pre>
  */
+@Deprecated
 public abstract class UiMessageHandler {
 
     private final Set<String> messageTypes;
diff --git a/core/api/src/main/java/org/onosproject/ui/UiMessageHandlerFactory.java b/core/api/src/main/java/org/onosproject/ui/UiMessageHandlerFactory.java
index 522daa8..23bd5d4 100644
--- a/core/api/src/main/java/org/onosproject/ui/UiMessageHandlerFactory.java
+++ b/core/api/src/main/java/org/onosproject/ui/UiMessageHandlerFactory.java
@@ -28,6 +28,6 @@
      *
      * @return collection of new handlers
      */
-    Collection<UiMessageHandler> newHandlers();
+    Collection<UiMessageHandlerTwo> newHandlers();
 
 }
diff --git a/core/api/src/main/java/org/onosproject/ui/UiMessageHandlerTwo.java b/core/api/src/main/java/org/onosproject/ui/UiMessageHandlerTwo.java
new file mode 100644
index 0000000..915bcaf
--- /dev/null
+++ b/core/api/src/main/java/org/onosproject/ui/UiMessageHandlerTwo.java
@@ -0,0 +1,169 @@
+/*
+ * 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);
+    }
+
+}
diff --git a/core/api/src/main/java/org/onosproject/ui/table/AbstractTableRow.java b/core/api/src/main/java/org/onosproject/ui/table/AbstractTableRow.java
index 32a4396..5dd11a4 100644
--- a/core/api/src/main/java/org/onosproject/ui/table/AbstractTableRow.java
+++ b/core/api/src/main/java/org/onosproject/ui/table/AbstractTableRow.java
@@ -73,4 +73,19 @@
     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();
+    }
 }