ONOS-2957 added loding configuration component from file.

Change-Id: I916470e80252dbbc014d31777b55ba20ea199d80

+/*
+ * 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.cfg.impl;
+
+import com.fasterxml.jackson.databind.ObjectMapper;
+import com.fasterxml.jackson.databind.node.ObjectNode;
+import com.google.common.collect.ImmutableSet;
+import com.google.common.collect.Sets;
+import org.apache.felix.scr.annotations.Activate;
+import org.apache.felix.scr.annotations.Component;
+import org.apache.felix.scr.annotations.Reference;
+import org.apache.felix.scr.annotations.ReferenceCardinality;
+import org.onlab.util.SharedExecutors;
+import org.onosproject.cfg.ComponentConfigService;
+import org.slf4j.Logger;
+
+import java.io.File;
+import java.util.Set;
+import java.util.TimerTask;
+
+import static org.slf4j.LoggerFactory.getLogger;
+
+/**
+ * Component responsible for automatically loading configuration file from
+ * configuration directory.
+ */
+@Component(immediate = true)
+public class ComponentConfigLoader {
+
+    private static final File CFG_FILE = new File("../config/component-cfg.json");
+    private static final int RETRY_DELAY = 5_000; // millis between retries
+
+    private final Logger log = getLogger(getClass());
+
+    @Reference(cardinality = ReferenceCardinality.MANDATORY_UNARY)
+    protected ComponentConfigService configService;
+
+    private ObjectNode root;
+    private final Set<String> pendingComponents = Sets.newHashSet();
+
+
+    /* TimerTask object that calls the load configuration for each component in the
+    pending components set and cancels itself if the set is mpty.
+    */
+    private final TimerTask loader = new TimerTask() {
+        @Override
+        public void run() {
+            ImmutableSet.copyOf(pendingComponents)
+                    .forEach(k -> loadConfig(k, (ObjectNode) root.path(k)));
+            if (pendingComponents.isEmpty()) {
+                this.cancel();
+            }
+        }
+    };
+
+    @Activate
+    protected void activate() {
+        this.loadConfigs();
+        log.info("Started");
+    }
+    /* loads the configurations for each component from the file in
+    ../config/component-cfg.json, adds them to a set and schedules a task to try
+    and load them.
+    */
+    private void loadConfigs() {
+        try {
+            if (CFG_FILE.exists()) {
+                root = (ObjectNode) new ObjectMapper().readTree(CFG_FILE);
+                root.fieldNames().forEachRemaining(pendingComponents::add);
+                SharedExecutors.getTimer().schedule(loader, RETRY_DELAY, RETRY_DELAY);
+                log.info("Loaded initial component configuration from {}", CFG_FILE);
+            }
+        } catch (Exception e) {
+            log.warn("Unable to load initial component configuration from {}",
+                     CFG_FILE, e);
+        }
+    }
+    /*
+    * loads a configuration for a single component and removes it from the
+    * components set
+    */
+    private void loadConfig(String component, ObjectNode config) {
+        if (configService.getComponentNames().contains(component)) {
+            config.fieldNames()
+                    .forEachRemaining(k -> configService.setProperty(component, k,
+                                                                     config.path(k).asText()));
+            pendingComponents.remove(component);
+        }
+    }
+}

+{
+  "org.onosproject.proxyarp.ProxyArp": {
+    "ipv6NeighborDiscovery": true
+  }
+}
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