Deserialize derived class data

This will attempt to deserialize results into the odata.type that Graph responds with instead of the class that the request builder provides. This allows us to respond with a derived object to a base object call. It also allows a developer to successfully cast the response object from the base type to the expected derived type.

Author: Caitlin Bales (MSFT)

src/main/java/com/microsoft/graph/serializer/DefaultSerializer.java

@@ -22,6 +22,7 @@
 
 package com.microsoft.graph.serializer;
 
+import com.google.common.base.CaseFormat;
 import com.google.gson.Gson;
 import com.google.gson.JsonElement;
 import com.google.gson.JsonObject;
@@ -64,13 +65,20 @@ public DefaultSerializer(final ILogger logger) {
      */
     @Override
     public <T> T deserializeObject(final String inputString, final Class<T> clazz) {
-        final T jsonObject = gson.fromJson(inputString, clazz);
+        T jsonObject = gson.fromJson(inputString, clazz);
 
-        // Populate the json backed fields for any annotations that are not in the object model
+        // Populate the JSON-backed fields for any annotations that are not in the object model
         if (jsonObject instanceof IJsonBackedObject) {
             logger.logDebug("Deserializing type " + clazz.getSimpleName());
             final IJsonBackedObject jsonBackedObject = (IJsonBackedObject) jsonObject;
             final JsonObject rawObject = gson.fromJson(inputString, JsonObject.class);
+            
+        	// If there is a derived class, try to get it and deserialize to it
+			Class derivedClass = this.getDerivedClass(rawObject);
+			if (derivedClass != null) {
+				jsonObject = (T) gson.fromJson(inputString, derivedClass);
+			}
+			
             jsonBackedObject.setRawObject(this, rawObject);
             jsonBackedObject.additionalDataManager().setAdditionalData(rawObject);
         } else {
@@ -116,4 +124,32 @@ public <T> String serializeObject(final T serializableObject) {
     private boolean fieldIsOdataTransient(Map.Entry<String, JsonElement> entry) {
         return entry.getKey().startsWith("@");
     }
+    
+    /**
+     * Get the derived class for the given JSON object
+     * This covers scenarios in which the service may return one of several derived types
+     * of a base object, which it defines using the odata.type parameter
+     * @param jsonObject The raw JSON object of the response
+     * @return The derived class if found, or null if not applicable
+     */
+    private Class getDerivedClass(JsonObject jsonObject) {
+    	//Identify the odata.type information if provided
+        if (jsonObject.get("@odata.type") != null) {
+        	String odataType = jsonObject.get("@odata.type").getAsString();
+        	String derivedType = odataType.substring(odataType.lastIndexOf('.') + 1); //Remove microsoft.graph prefix
+        	derivedType = CaseFormat.LOWER_CAMEL.to(CaseFormat.UPPER_CAMEL, derivedType);
+        	derivedType = "com.microsoft.graph.models.extensions." + derivedType; //Add full package path
+        	
+        	try {
+        		return Class.forName(derivedType);
+        	} catch (ClassNotFoundException e) {
+        		logger.logDebug("Unable to find a corresponding class for derived type " + derivedType + ". Falling back to parent class.");
+        		//If we cannot determine the derived type to cast to, return null
+        		//This may happen if the API and the SDK are out of sync
+        		return null;
+        	}
+        }
+        //If there is no defined OData type, return null
+        return null;
+    }
 }