Adding new REST API resource to obtain system level summary.

Change-Id: Ia3ce18a50a56aa19d07b594990d3136a7ef07706
diff --git a/web/api/src/main/java/org/onosproject/rest/resources/CoreWebApplication.java b/web/api/src/main/java/org/onosproject/rest/resources/CoreWebApplication.java
index f1ca75f..85997dc 100644
--- a/web/api/src/main/java/org/onosproject/rest/resources/CoreWebApplication.java
+++ b/web/api/src/main/java/org/onosproject/rest/resources/CoreWebApplication.java
@@ -54,7 +54,8 @@
                 InvalidConfigExceptionMapper.class,
                 DpisWebResource.class,
                 DiagnosticsWebResource.class,
-                UiPreferencesWebResource.class
+                UiPreferencesWebResource.class,
+                SystemInfoWebResource.class
         );
     }
 }
diff --git a/web/api/src/main/java/org/onosproject/rest/resources/SystemInfoWebResource.java b/web/api/src/main/java/org/onosproject/rest/resources/SystemInfoWebResource.java
new file mode 100644
index 0000000..006c21c
--- /dev/null
+++ b/web/api/src/main/java/org/onosproject/rest/resources/SystemInfoWebResource.java
@@ -0,0 +1,103 @@
+/*
+ * Copyright 2015-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.rest.resources;
+
+import com.fasterxml.jackson.databind.node.ObjectNode;
+import org.onlab.packet.IpAddress;
+import org.onosproject.cluster.ClusterMetadataService;
+import org.onosproject.cluster.ClusterService;
+import org.onosproject.cluster.ControllerNode;
+import org.onosproject.core.CoreService;
+import org.onosproject.core.Version;
+import org.onosproject.net.device.DeviceService;
+import org.onosproject.net.flow.FlowRuleService;
+import org.onosproject.net.host.HostService;
+import org.onosproject.net.intent.IntentService;
+import org.onosproject.net.link.LinkService;
+import org.onosproject.net.topology.TopologyService;
+import org.onosproject.rest.AbstractWebResource;
+
+import javax.ws.rs.GET;
+import javax.ws.rs.Path;
+import javax.ws.rs.Produces;
+import javax.ws.rs.core.MediaType;
+import javax.ws.rs.core.Response;
+import java.lang.management.ManagementFactory;
+import java.lang.management.MemoryUsage;
+import java.lang.management.ThreadMXBean;
+import java.util.Set;
+
+/**
+ * Provides high-level system information, version, basic sumaries, memory usage, etc.
+ */
+@Path("system")
+public class SystemInfoWebResource extends AbstractWebResource {
+
+    private long activeNodes(Set<ControllerNode> nodes) {
+        ClusterService clusterService = get(ClusterService.class);
+        return nodes.stream()
+                .map(node -> clusterService.getState(node.id()))
+                .filter(ControllerNode.State::isActive)
+                .count();
+    }
+
+    /**
+     * Get high-level system information, version, basic sumaries, memory usage, etc.
+     *
+     * @return 200 OK with a system summary
+     */
+    @GET
+    @Produces(MediaType.APPLICATION_JSON)
+    public Response getSystemInfo() {
+        IpAddress nodeIp = get(ClusterService.class).getLocalNode().ip();
+        Version version = get(CoreService.class).version();
+        long numNodes = activeNodes(get(ClusterService.class).getNodes());
+        int numDevices = get(DeviceService.class).getDeviceCount();
+        int numLinks = get(LinkService.class).getLinkCount();
+        int numHosts = get(HostService.class).getHostCount();
+        int numScc = get(TopologyService.class).currentTopology().clusterCount();
+        int numFlows = get(FlowRuleService.class).getFlowRuleCount();
+        long numIntents = get(IntentService.class).getIntentCount();
+        String clusterId = get(ClusterMetadataService.class).getClusterMetadata().getName();
+
+        ObjectNode root = mapper().createObjectNode()
+                .put("node", nodeIp.toString())
+                .put("version", version.toString())
+                .put("clusterId", clusterId)
+                .put("nodes", numNodes)
+                .put("devices", numDevices)
+                .put("links", numLinks)
+                .put("hosts", numHosts)
+                .put("sccs", numScc)
+                .put("flows", numFlows)
+                .put("intents", numIntents);
+
+        MemoryUsage mem = ManagementFactory.getMemoryMXBean().getHeapMemoryUsage();
+        newObject(root, "mem")
+                .put("current", mem.getUsed())
+                .put("max", mem.getMax())
+                .put("committed", mem.getCommitted());
+
+        ThreadMXBean threads = ManagementFactory.getThreadMXBean();
+        newObject(root, "threads")
+                .put("live", threads.getThreadCount())
+                .put("daemon", threads.getDaemonThreadCount())
+                .put("peak", threads.getPeakThreadCount());
+
+        return ok(root).build();
+    }
+
+}