Add zeppelinhub session container

zeppelin-zengine/src/main/java/org/apache/zeppelin/notebook/repo/zeppelinhub/model/UserSessionContainer.java

@@ -0,0 +1,54 @@
+/*
+ * 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.apache.zeppelin.notebook.repo.zeppelinhub.model;
+
+import java.util.Map;
+import java.util.concurrent.ConcurrentHashMap;
+
+import org.apache.commons.lang.StringUtils;
+
+/**
+ * Simple and yet dummy container for zeppelinhub session.
+ * 
+ */
+public class UserSessionContainer {
+  private static class Entity {
+    public final String userSession;
+
+    Entity(String userSession) {
+      this.userSession = userSession;
+    }
+  }
+
+  private Map<String, Entity> sessions = new ConcurrentHashMap<>();
+
+  public static final UserSessionContainer instance = new UserSessionContainer();
+
+  public synchronized String getSession(String principal) {
+    Entity entry = sessions.get(principal);
+    if (entry == null) {
+      return StringUtils.EMPTY;
+    }
+    return entry.userSession;
+  }
+  
+  public synchronized String setSession(String principal, String userSession) {
+    Entity entry = new Entity(userSession);
+    sessions.put(principal, entry);
+    return entry.userSession;
+  }
+}