feat(GraphQLTemplate) option to externalize fetching, Relates #70

nodes/src/main/java/io/aexp/nodes/graphql/Fetch.java

@@ -30,7 +30,7 @@
 import java.util.List;
 import java.util.Map;
 
-final class Fetch {
+final class Fetch implements Fetcher {
 
     private final ObjectMapperFactory objectMapperFactory;
     private ObjectMapper mapper;
@@ -41,7 +41,7 @@ final class Fetch {
         this.objectMapperFactory = objectMapperFactory;
     }
 
-    <T> GraphQLResponseEntity<T> send(GraphQLRequestEntity requestEntity, Class<T> responseClass) throws GraphQLException {
+    public <T> GraphQLResponseEntity<T> send(GraphQLRequestEntity requestEntity, Class<T> responseClass) throws GraphQLException {
         mapper = objectMapperFactory.newSerializerMapper();
         module = new SimpleModule();
 

nodes/src/main/java/io/aexp/nodes/graphql/Fetcher.java

@@ -0,0 +1,20 @@
+/*
+ * Copyright (c) 2018 American Express Travel Related Services Company, Inc.
+ *
+ * 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 io.aexp.nodes.graphql;
+
+import io.aexp.nodes.graphql.exceptions.GraphQLException;
+
+public interface Fetcher {
+    <T> GraphQLResponseEntity<T> send(GraphQLRequestEntity requestEntity, Class<T> responseClass) throws GraphQLException;
+}

nodes/src/main/java/io/aexp/nodes/graphql/GraphQLTemplate.java

@@ -18,7 +18,7 @@
 
 public class GraphQLTemplate {
 
-    private Fetch fetch;
+    private Fetcher fetch;
 
     public enum GraphQLMethod {
         QUERY("query"),
@@ -45,7 +45,15 @@ public GraphQLTemplate() {
      * @param objectMapperFactory factory class used for creating ObjectMapper instances
      */
     public GraphQLTemplate(final ObjectMapperFactory objectMapperFactory) {
-        fetch = new Fetch(objectMapperFactory);
+        this(new Fetch(objectMapperFactory));
+    }
+
+    /**
+     * Constructs a new GraphQL template instance using the specified ObjectMapper factory.
+     * @param fetcher custom fetch provider
+     */
+    public GraphQLTemplate(final Fetcher fetcher) {
+        fetch = fetcher;
     }
 
     /**