[ONOS-3203] Optimize alarms codec registration.

Updating as advised at :
https://gerrit.onosproject.org/#/c/6180/3/apps/faultmanagement/fmweb/src/main/java/org/onosproject/faultmanagement/web/AlarmsWebResource.java@53

Copying the approach used in equivalent app at vtn/vtnweb/src/main/java/org/onosproject/vtnweb/web/VtnCodecRegistrator.java

Change-Id: Ifdcf5d69fe28070161e138217582126b135504a7

+/*
+ * Copyright 2014-2015 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.faultmanagement.web;
+
+import org.apache.felix.scr.annotations.Activate;
+import org.apache.felix.scr.annotations.Component;
+import org.apache.felix.scr.annotations.Deactivate;
+import org.apache.felix.scr.annotations.Reference;
+import org.apache.felix.scr.annotations.ReferenceCardinality;
+import org.onosproject.codec.CodecService;
+import org.onosproject.incubator.net.faultmanagement.alarm.Alarm;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/**
+ * Implementation of the JSON codec brokering service for FM app.
+ */
+@Component(immediate = true)
+public class AlarmCodecRegistrator {
+
+    private static final Logger log = LoggerFactory.getLogger(AlarmCodecRegistrator.class);
+
+    @Reference(cardinality = ReferenceCardinality.MANDATORY_UNARY)
+    protected CodecService codecService;
+
+    @Activate
+    public void activate() {
+        codecService.registerCodec(Alarm.class, new AlarmCodec());
+        log.info("Started");
+    }
+
+    @Deactivate
+    public void deactivate() {
+        log.info("Stopped");
+    }
+}

@@ -34,7 +34,6 @@ import javax.ws.rs.PathParam;
 import javax.ws.rs.Produces;
 import javax.ws.rs.QueryParam;
 import javax.ws.rs.core.MediaType;
-import org.onosproject.codec.CodecService;
 import org.onosproject.incubator.net.faultmanagement.alarm.AlarmService;
 import org.slf4j.Logger;
 import static org.slf4j.LoggerFactory.getLogger;
@@ -50,7 +49,6 @@ public class AlarmsWebResource extends AbstractWebResource {
     private final Logger log = getLogger(getClass());
 
     public AlarmsWebResource() {
-        get(CodecService.class).registerCodec(Alarm.class, new AlarmCodec());
     }
 
     /**

@@ -15,15 +15,12 @@
  */
 package org.onosproject.faultmanagement.web;
 
-import java.util.Map;
-import java.util.concurrent.ConcurrentHashMap;
-
 import org.onosproject.codec.CodecContext;
+import org.onosproject.codec.CodecService;
 import org.onosproject.codec.JsonCodec;
-
+import org.onosproject.codec.impl.CodecManager;
 
 import com.fasterxml.jackson.databind.ObjectMapper;
-import org.onosproject.incubator.net.faultmanagement.alarm.Alarm;
 
 /**
  * Mock codec context for use in codec unit tests.
@@ -31,15 +28,16 @@ import org.onosproject.incubator.net.faultmanagement.alarm.Alarm;
 public class AlarmCodecContext implements CodecContext {
 
     private final ObjectMapper mapper = new ObjectMapper();
-    private final Map<Class<?>, JsonCodec> codecs = new ConcurrentHashMap<>();
+    private final CodecManager codecManager = new CodecManager();
+    private final AlarmCodecRegistrator manager = new AlarmCodecRegistrator();
 
     /**
      * Constructs a new mock codec context.
      */
     public AlarmCodecContext() {
-        codecs.clear();
-        registerCodec(Alarm.class, new AlarmCodec());
-
+        codecManager.activate();
+        manager.codecService = codecManager;
+        manager.activate();
     }
 
     @Override
@@ -50,24 +48,20 @@ public class AlarmCodecContext implements CodecContext {
     @SuppressWarnings("unchecked")
     @Override
     public <T> T getService(Class<T> serviceClass) {
-        // TODO
         return null;
     }
 
+    @Override
+    public <T> JsonCodec<T> codec(Class<T> entityClass) {
+        return codecManager.getCodec(entityClass);
+    }
+
     /**
-     * Registers the specified JSON codec for the given entity class.
+     * Get the codec manager.
      *
-     * @param entityClass entity class
-     * @param codec       JSON codec
-     * @param <T>         entity type
+     * @return instance of codec manager
      */
-    public <T> void registerCodec(Class<T> entityClass, JsonCodec<T> codec) {
-        codecs.putIfAbsent(entityClass, codec);
-    }
-
-    @SuppressWarnings("unchecked")
-    @Override
-    public <T> JsonCodec<T> codec(Class<T> entityClass) {
-        return codecs.get(entityClass);
+    public CodecService codecManager() {
+        return codecManager;
     }
 }