User Profile Service Interface (#95)

* create UserProfileService interface
* add descriptions for lookup and save. 
* change method signature for save profile
* add throws to all customer implemented methods so we will wrap around it and catch possible exceptions

Author: wangjoshuah

core-api/src/main/java/com/optimizely/ab/bucketing/UserProfileService.java

@@ -0,0 +1,44 @@
+/**
+ *
+ *    Copyright 2017, Optimizely and contributors
+ *
+ *    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 com.optimizely.ab.bucketing;
+
+import java.util.Map;
+
+/**
+ * Class encapsulating user profile service functionality.
+ *
+ * Override with your own implementation for storing and retrieving the user profile.
+ */
+public interface UserProfileService {
+
+    /**
+     * Fetch the user profile map for the user ID.
+     *
+     * @param userId The ID of the user whose profile will be retrieved.
+     * @return a Map representing the user's profile.
+     * @throws Exception 
+     */
+    Map<String, Object> lookup(String userId) throws Exception;
+
+    /**
+     * Save the user profile Map sent to this method.
+     *
+     * @param userProfile The Map representing the user's profile.
+     * @throws Exception Can throw an exception if the user profile was not saved properly.
+     */
+    void save(Map<String, Object> userProfile) throws Exception;
+}