chore(aws-api-appsync): consolidate serde logic (#875)

Around the code base, Gson is used with various different
configurations. However, most uses require the same basic set of
serializers and deserializers, to handle custom Amplify and AppSync
types.

To address this, the serializers and deserializers are consolidated
(mostly) into the aws-api-appsync module. Gson construction now occurs
uniformy from the provided GsonFactory.

Resolves: #848

Author: jamesonwilliams

aws-api-appsync/src/main/java/com/amplifyframework/api/aws/GsonVariablesSerializer.java

@@ -16,20 +16,10 @@
 package com.amplifyframework.api.aws;
 
 import com.amplifyframework.api.graphql.GraphQLRequest;
-import com.amplifyframework.core.model.temporal.Temporal;
+import com.amplifyframework.util.GsonFactory;
 
 import com.google.gson.Gson;
-import com.google.gson.GsonBuilder;
-import com.google.gson.JsonElement;
-import com.google.gson.JsonPrimitive;
-import com.google.gson.JsonSerializationContext;
-import com.google.gson.JsonSerializer;
 
-import java.lang.reflect.Type;
-import java.text.DateFormat;
-import java.text.SimpleDateFormat;
-import java.util.Date;
-import java.util.Locale;
 import java.util.Map;
 
 /**
@@ -39,16 +29,20 @@ public final class GsonVariablesSerializer implements GraphQLRequest.VariablesSe
     private final Gson gson;
 
     /**
-     * Creates new instance of GsonVariablesSerializer.
+     * Creates a new instance of GsonVariablesSerializer, using a
+     * default Gson instance.
      */
     public GsonVariablesSerializer() {
-        gson = new GsonBuilder()
-            .registerTypeAdapter(Date.class, new DateSerializer())
-            .registerTypeAdapter(Temporal.Timestamp.class, new TemporalTimestampSerializer())
-            .registerTypeAdapter(Temporal.Date.class, new TemporalDateSerializer())
-            .registerTypeAdapter(Temporal.DateTime.class, new TemporalDateTimeSerializer())
-            .registerTypeAdapter(Temporal.Time.class, new TemporalTimeSerializer())
-            .create();
+        this(GsonFactory.instance());
+    }
+
+    /**
+     * Creates a new instance of GsonVariablesSerializer, using a custom
+     * Gson instance.
+     * @param gson Gson instance to use for serialization
+     */
+    public GsonVariablesSerializer(Gson gson) {
+        this.gson = gson;
     }
 
     @Override
@@ -61,82 +55,11 @@ public boolean equals(Object thatObject) {
         if (this == thatObject) {
             return true;
         }
-        if (thatObject == null || getClass() != thatObject.getClass()) {
-            return false;
-        }
-
-        return true;
+        return thatObject != null && getClass() == thatObject.getClass();
     }
 
     @Override
     public int hashCode() {
         return 0;
     }
-
-    /**
-     * Serializer of {@link Temporal.Date}, an extended ISO-8601 Date string, with an optional timezone offset.
-     *
-     * https://docs.aws.amazon.com/appsync/latest/devguide/scalars.html
-     */
-    static class TemporalDateSerializer implements JsonSerializer<Temporal.Date> {
-        @Override
-        public JsonElement serialize(Temporal.Date date, Type typeOfSrc, JsonSerializationContext context) {
-            return new JsonPrimitive(date.format());
-        }
-    }
-
-    /**
-     * Serializer of {@link Temporal.DateTime}, an extended ISO-8601 DateTime string.
-     * Time zone offset is required.
-     *
-     * https://docs.aws.amazon.com/appsync/latest/devguide/scalars.html
-     */
-    static class TemporalDateTimeSerializer implements JsonSerializer<Temporal.DateTime> {
-        @Override
-        public JsonElement serialize(Temporal.DateTime dateTime, Type typeOfSrc, JsonSerializationContext context) {
-            return new JsonPrimitive(dateTime.format());
-        }
-    }
-
-    /**
-     * Serializer of {@link Temporal.Time}, an extended ISO-8601 Time string, with an optional timezone offset.
-     *
-     * https://docs.aws.amazon.com/appsync/latest/devguide/scalars.html
-     */
-    static class TemporalTimeSerializer implements JsonSerializer<Temporal.Time> {
-        @Override
-        public JsonElement serialize(Temporal.Time time, Type typeOfSrc, JsonSerializationContext context) {
-            return new JsonPrimitive(time.format());
-        }
-    }
-
-    /**
-     * Serializer of {@link Temporal.Timestamp}, an AppSync scalar type that represents
-     * the number of seconds elapsed since 1970-01-01T00:00Z. Timestamps are serialized as numbers.
-     * Negative values are also accepted and these represent the number of seconds till 1970-01-01T00:00Z.
-     *
-     * https://docs.aws.amazon.com/appsync/latest/devguide/scalars.html
-     */
-    static class TemporalTimestampSerializer implements JsonSerializer<Temporal.Timestamp> {
-        @Override
-        public JsonElement serialize(Temporal.Timestamp timestamp, Type typeOfSrc, JsonSerializationContext context) {
-            return new JsonPrimitive(timestamp.getSecondsSinceEpoch());
-        }
-    }
-
-    /**
-     * Earlier versions of the model gen used to use Java's {@link Date} to represent all of the
-     * temporal types. This led to challenges while trying to decode/encode the timezone,
-     * among other things. The model gen will now spit out {@link Temporal.Date}, {@link Temporal.DateTime},
-     * {@link Temporal.Time}, and {@link Temporal.Timestamp}, instead. This DateSerializer is left for
-     * compat, until such a time as it can be safely removed (that is, when all models no longer
-     * use a raw Date type.)
-     */
-    static class DateSerializer implements JsonSerializer<Date> {
-        @Override
-        public JsonElement serialize(Date date, Type typeOfSrc, JsonSerializationContext context) {
-            DateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd", Locale.getDefault());
-            return new JsonPrimitive(dateFormat.format(date));
-        }
-    }
 }