Added application ID store; both trivial and distributed variants.
diff --git a/core/store/trivial/src/main/java/org/onlab/onos/store/trivial/impl/SimpleApplicationIdStore.java b/core/store/trivial/src/main/java/org/onlab/onos/store/trivial/impl/SimpleApplicationIdStore.java
new file mode 100644
index 0000000..a242822
--- /dev/null
+++ b/core/store/trivial/src/main/java/org/onlab/onos/store/trivial/impl/SimpleApplicationIdStore.java
@@ -0,0 +1,68 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you 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.onlab.onos.store.trivial.impl;
+
+import com.google.common.collect.ImmutableSet;
+import org.apache.felix.scr.annotations.Component;
+import org.apache.felix.scr.annotations.Service;
+import org.onlab.onos.core.ApplicationId;
+import org.onlab.onos.core.ApplicationIdStore;
+import org.onlab.onos.core.DefaultApplicationId;
+
+import java.util.Map;
+import java.util.Set;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.atomic.AtomicInteger;
+
+/**
+ * Simple implementation of the application ID registry using in-memory
+ * structures.
+ */
+@Component(immediate = true)
+@Service
+public class SimpleApplicationIdStore implements ApplicationIdStore {
+
+    private static final AtomicInteger ID_DISPENSER = new AtomicInteger(1);
+
+    private final Map<Short, DefaultApplicationId> appIds = new ConcurrentHashMap<>();
+    private final Map<String, DefaultApplicationId> appIdsByName = new ConcurrentHashMap<>();
+
+    @Override
+    public Set<ApplicationId> getAppIds() {
+        return ImmutableSet.<ApplicationId>copyOf(appIds.values());
+    }
+
+    @Override
+    public ApplicationId getAppId(Short id) {
+        return appIds.get(id);
+    }
+
+    @Override
+    public ApplicationId registerApplication(String name) {
+        DefaultApplicationId appId = appIdsByName.get(name);
+        if (appId == null) {
+            short id = (short) ID_DISPENSER.getAndIncrement();
+            appId = new DefaultApplicationId(id, name);
+            appIds.put(id, appId);
+            appIdsByName.put(name, appId);
+        }
+        return appId;
+    }
+
+}