Added deserialization helpers for custom Enums

Author: JanHolger

src/main/java/org/javawebstack/graph/util/GsonEnum.java

@@ -0,0 +1,5 @@
+package org.javawebstack.graph.util;
+
+public interface GsonEnum {
+    String gsonValue();
+}

src/main/java/org/javawebstack/graph/util/GsonEnumAdapter.java

@@ -0,0 +1,31 @@
+package org.javawebstack.graph.util;
+
+import com.google.gson.*;
+
+import java.lang.reflect.Type;
+
+public class GsonEnumAdapter implements JsonSerializer<GsonEnum>, JsonDeserializer<GsonEnum> {
+
+    public GsonEnum deserialize(JsonElement jsonElement, Type type, JsonDeserializationContext jsonDeserializationContext) throws JsonParseException {
+        if(jsonElement == null || !jsonElement.isJsonPrimitive() || !jsonElement.getAsJsonPrimitive().isString())
+            return null;
+        String value = jsonElement.getAsJsonPrimitive().getAsString();
+        if(!(type instanceof Class))
+            return null;
+        Class<GsonEnum> typeClass = (Class<GsonEnum>) type;
+        if(!GsonEnum.class.isAssignableFrom(typeClass))
+            return null;
+        if(!typeClass.isEnum())
+            return null;
+        for(GsonEnum e : typeClass.getEnumConstants()){
+            if(e.gsonValue().equals(value))
+                return e;
+        }
+        return null;
+    }
+
+    public JsonElement serialize(GsonEnum gsonEnum, Type type, JsonSerializationContext jsonSerializationContext) {
+        return new JsonPrimitive(gsonEnum.gsonValue());
+    }
+
+}