Made changes as per comments.
kafkaProducer is now non-static.

TODO: KafkaPublisherManager Service and not Singleton.
Kafka event publishing.

Change-Id: I5ec20a6e4950c38e822468d343521ab77475b7d3
diff --git a/apps/kafka-integration/core/src/main/java/org/onosproject/kafkaintegration/converter/ConversionFactory.java b/apps/kafka-integration/core/src/main/java/org/onosproject/kafkaintegration/converter/ConversionFactory.java
new file mode 100644
index 0000000..26b5060
--- /dev/null
+++ b/apps/kafka-integration/core/src/main/java/org/onosproject/kafkaintegration/converter/ConversionFactory.java
@@ -0,0 +1,68 @@
+/**
+ * Copyright 2016 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.kafkaintegration.converter;
+
+import org.onosproject.kafkaintegration.api.dto.OnosEvent.Type;
+
+import java.util.HashMap;
+import java.util.Map;
+
+import static org.onosproject.kafkaintegration.api.dto.OnosEvent.Type.DEVICE;
+import static org.onosproject.kafkaintegration.api.dto.OnosEvent.Type.LINK;
+
+/**
+ * Returns the appropriate converter object based on the ONOS event type.
+ *
+ */
+public final class ConversionFactory {
+
+    // Store converters for all supported events
+    private Map<Type, EventConverter> converters =
+            new HashMap<Type, EventConverter>() {
+                {
+                    put(DEVICE, new DeviceEventConverter());
+                    put(LINK, new LinkEventConverter());
+                }
+            };
+
+    // Exists to defeat instantiation
+    private ConversionFactory() {
+    }
+
+    private static class SingletonHolder {
+        private static final ConversionFactory INSTANCE =
+                new ConversionFactory();
+    }
+
+    /**
+     * Returns a static reference to the Conversion Factory.
+     *
+     * @return singleton object
+     */
+    public static ConversionFactory getInstance() {
+        return SingletonHolder.INSTANCE;
+    }
+
+    /**
+     * Returns an Event converter object for the specified ONOS event type.
+     *
+     * @param event ONOS event type
+     * @return Event Converter object
+     */
+    public EventConverter getConverter(Type event) {
+        return converters.get(event);
+    }
+
+}
diff --git a/apps/kafka-integration/core/src/main/java/org/onosproject/kafkaintegration/converter/DeviceEventConverter.java b/apps/kafka-integration/core/src/main/java/org/onosproject/kafkaintegration/converter/DeviceEventConverter.java
new file mode 100644
index 0000000..6b2ee24
--- /dev/null
+++ b/apps/kafka-integration/core/src/main/java/org/onosproject/kafkaintegration/converter/DeviceEventConverter.java
@@ -0,0 +1,122 @@
+/**
+ * Copyright 2016 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.kafkaintegration.converter;
+
+import com.google.protobuf.GeneratedMessage;
+import org.onosproject.event.Event;
+import org.onosproject.grpc.net.Device.DeviceCore;
+import org.onosproject.grpc.net.Device.DeviceType;
+import org.onosproject.grpc.net.DeviceEvent.DeviceEventType;
+import org.onosproject.grpc.net.DeviceEvent.DeviceNotification;
+import org.onosproject.grpc.net.Port.PortCore;
+import org.onosproject.grpc.net.Port.PortType;
+import org.onosproject.net.device.DeviceEvent;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/**
+ * Converts ONOS Device event message to protobuf format.
+ */
+public class DeviceEventConverter implements EventConverter {
+
+    private final Logger log = LoggerFactory.getLogger(getClass());
+
+    @Override
+    public GeneratedMessage convertToProtoMessage(Event<?, ?> event) {
+
+        DeviceEvent deviceEvent = (DeviceEvent) event;
+
+        if (!deviceEventTypeSupported(deviceEvent)) {
+            log.error("Unsupported Onos Device Event {}. There is no matching"
+                    + "proto Device Event type", deviceEvent.type().toString());
+            return null;
+        }
+
+        return buildDeviceProtoMessage(deviceEvent);
+    }
+
+    /**
+     * Checks if the ONOS Device Event type is supported.
+     *
+     * @param event ONOS Device event
+     * @return true if there is a match and false otherwise
+     */
+    private boolean deviceEventTypeSupported(DeviceEvent event) {
+        DeviceEventType[] deviceEvents = DeviceEventType.values();
+        for (DeviceEventType deviceEventType : deviceEvents) {
+            if (deviceEventType.name().equals(event.type().name())) {
+                return true;
+            }
+        }
+
+        return false;
+    }
+
+    private DeviceNotification buildDeviceProtoMessage(DeviceEvent deviceEvent) {
+        DeviceNotification.Builder notificationBuilder =
+                DeviceNotification.newBuilder();
+
+        DeviceCore deviceCore =
+                DeviceCore.newBuilder()
+                        .setChassisId(deviceEvent.subject().chassisId().id()
+                                              .toString())
+                        .setDeviceId(deviceEvent.subject().id().toString())
+                        .setHwVersion(deviceEvent.subject().hwVersion())
+                        .setManufacturer(deviceEvent.subject().manufacturer())
+                        .setSerialNumber(deviceEvent.subject().serialNumber())
+                        .setSwVersion(deviceEvent.subject().swVersion())
+                        .setType(DeviceType
+                                         .valueOf(deviceEvent.subject().type().name()))
+                        .build();
+
+        PortCore portCore = null;
+        if (deviceEvent.port() != null) {
+            portCore =
+                    PortCore.newBuilder()
+                            .setIsEnabled(deviceEvent.port().isEnabled())
+                            .setPortNumber(deviceEvent.port().number()
+                                                   .toString())
+                            .setPortSpeed(deviceEvent.port().portSpeed())
+                            .setType(PortType
+                                             .valueOf(deviceEvent.port().type().name()))
+                            .build();
+
+            notificationBuilder.setPort(portCore);
+        }
+
+        notificationBuilder.setDeviceEventType(getProtoType(deviceEvent))
+                .setDevice(deviceCore);
+
+        return notificationBuilder.build();
+    }
+
+    /**
+     * Retrieves the protobuf generated device event type.
+     *
+     * @param event ONOS Device Event
+     * @return generated Device Event Type
+     */
+    private DeviceEventType getProtoType(DeviceEvent event) {
+        DeviceEventType protobufEventType = null;
+        DeviceEventType[] deviceEvents = DeviceEventType.values();
+        for (DeviceEventType deviceEventType : deviceEvents) {
+            if (deviceEventType.name().equals(event.type().name())) {
+                protobufEventType = deviceEventType;
+            }
+        }
+
+        return protobufEventType;
+    }
+}
diff --git a/apps/kafka-integration/core/src/main/java/org/onosproject/kafkaintegration/converter/EventConverter.java b/apps/kafka-integration/core/src/main/java/org/onosproject/kafkaintegration/converter/EventConverter.java
new file mode 100644
index 0000000..c1e7739
--- /dev/null
+++ b/apps/kafka-integration/core/src/main/java/org/onosproject/kafkaintegration/converter/EventConverter.java
@@ -0,0 +1,36 @@
+/**
+ * Copyright 2016 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.kafkaintegration.converter;
+
+import org.onosproject.event.Event;
+
+import com.google.protobuf.GeneratedMessage;
+
+/**
+ *
+ * APIs for converting between ONOS event objects and protobuf data objects.
+ *
+ */
+public interface EventConverter {
+
+    /**
+     * Converts ONOS specific event data to a format that is suitable for export
+     * to Kafka.
+     *
+     * @param event ONOS Event object
+     * @return converted data in protobuf format.
+     */
+    GeneratedMessage convertToProtoMessage(Event<?, ?> event);
+}
diff --git a/apps/kafka-integration/core/src/main/java/org/onosproject/kafkaintegration/converter/LinkEventConverter.java b/apps/kafka-integration/core/src/main/java/org/onosproject/kafkaintegration/converter/LinkEventConverter.java
new file mode 100644
index 0000000..febe020
--- /dev/null
+++ b/apps/kafka-integration/core/src/main/java/org/onosproject/kafkaintegration/converter/LinkEventConverter.java
@@ -0,0 +1,101 @@
+/**
+ * Copyright 2016 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.kafkaintegration.converter;
+
+import org.onosproject.event.Event;
+import org.onosproject.grpc.net.Link.ConnectPoint;
+import org.onosproject.grpc.net.Link.LinkCore;
+import org.onosproject.grpc.net.Link.LinkState;
+import org.onosproject.grpc.net.Link.LinkType;
+import org.onosproject.grpc.net.LinkEvent.LinkEventType;
+import org.onosproject.grpc.net.LinkEvent.LinkNotification;
+import org.onosproject.net.link.LinkEvent;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import com.google.protobuf.GeneratedMessage;
+
+/**
+ * Converts for ONOS Link event message to protobuf format.
+ */
+public class LinkEventConverter implements EventConverter {
+
+    private final Logger log = LoggerFactory.getLogger(getClass());
+
+    @Override
+    public GeneratedMessage convertToProtoMessage(Event<?, ?> event) {
+
+        LinkEvent linkEvent = (LinkEvent) event;
+
+        if (!linkEventTypeSupported(linkEvent)) {
+            log.error("Unsupported Onos Event {}. There is no matching "
+                    + "proto Event type", linkEvent.type().toString());
+            return null;
+        }
+
+        return buildDeviceProtoMessage(linkEvent);
+    }
+
+    private boolean linkEventTypeSupported(LinkEvent event) {
+        LinkEventType[] kafkaLinkEvents = LinkEventType.values();
+        for (LinkEventType linkEventType : kafkaLinkEvents) {
+            if (linkEventType.name().equals(event.type().name())) {
+                return true;
+            }
+        }
+        return false;
+    }
+
+    private LinkNotification buildDeviceProtoMessage(LinkEvent linkEvent) {
+        LinkNotification notification = LinkNotification.newBuilder()
+                .setLinkEventType(getProtoType(linkEvent))
+                .setLink(LinkCore.newBuilder()
+                        .setState(LinkState
+                                .valueOf(linkEvent.subject().state().name()))
+                        .setType(LinkType.valueOf(linkEvent.subject().type().name()))
+                        .setDst(ConnectPoint.newBuilder()
+                                .setDeviceId(linkEvent.subject().dst()
+                                        .deviceId().toString())
+                                .setPortNumber(linkEvent.subject().dst().port()
+                                        .toString()))
+                        .setSrc(ConnectPoint.newBuilder()
+                                .setDeviceId(linkEvent.subject().src()
+                                        .deviceId().toString())
+                                .setPortNumber(linkEvent.subject().src().port()
+                                        .toString())))
+                .build();
+
+        return notification;
+    }
+
+    /**
+     * Returns the specific Kafka Device Event Type for the corresponding ONOS
+     * Device Event Type.
+     *
+     * @param event ONOS Device Event
+     * @return Kafka Device Event Type
+     */
+    private LinkEventType getProtoType(LinkEvent event) {
+        LinkEventType generatedEventType = null;
+        LinkEventType[] kafkaEvents = LinkEventType.values();
+        for (LinkEventType linkEventType : kafkaEvents) {
+            if (linkEventType.name().equals(event.type().name())) {
+                generatedEventType = linkEventType;
+            }
+        }
+
+        return generatedEventType;
+    }
+}
diff --git a/apps/kafka-integration/core/src/main/java/org/onosproject/kafkaintegration/converter/package-info.java b/apps/kafka-integration/core/src/main/java/org/onosproject/kafkaintegration/converter/package-info.java
new file mode 100644
index 0000000..d33c0d7
--- /dev/null
+++ b/apps/kafka-integration/core/src/main/java/org/onosproject/kafkaintegration/converter/package-info.java
@@ -0,0 +1,20 @@
+/**
+ * Copyright 2016-present 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.
+ */
+
+/**
+ * Converters for converting various ONOS events to their corresponding Protocol
+ * Buffer format.
+ *
+ */
+package org.onosproject.kafkaintegration.converter;