Initial implementation of XMPP Publish/Subscribe

Change-Id: I9930056b83004fa7a085f72f63ba973f9ec2d95b
diff --git a/protocols/xmpp/pubsub/api/src/main/java/org/onosproject/xmpp/pubsub/model/XmppEventNotification.java b/protocols/xmpp/pubsub/api/src/main/java/org/onosproject/xmpp/pubsub/model/XmppEventNotification.java
new file mode 100644
index 0000000..a4e64b7
--- /dev/null
+++ b/protocols/xmpp/pubsub/api/src/main/java/org/onosproject/xmpp/pubsub/model/XmppEventNotification.java
@@ -0,0 +1,45 @@
+/*
+ * Copyright 2018-present Open Networking Foundation
+ *
+ * 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.xmpp.pubsub.model;
+
+import org.dom4j.Element;
+import org.xmpp.packet.Message;
+
+import static org.onosproject.xmpp.pubsub.XmppPubSubConstants.PUBSUB_EVENT_NS;
+
+/**
+ * Abstracts Event Notification message of XMPP PubSub protocol.
+ */
+public class XmppEventNotification extends Message {
+
+    /**
+     * Constructor for XmppEventNotification class. It generates representation
+     * of XMPP NOTIFY message.
+     *
+     * @param node node attribute of PubSub extension
+     * @param payload XML payload for XMPP NOTIFY message
+     */
+    public XmppEventNotification(String node, Element payload) {
+        super(docFactory.createDocument().addElement("message"));
+        this.addChildElement("event", PUBSUB_EVENT_NS);
+        Element items = docFactory.createElement("items");
+        items.addAttribute("node", node);
+        items.add(payload);
+        this.getElement().element("event").add(items);
+    }
+
+}