Make GraphQL execution strategies configurable by an 'ExecutionStrate…

…gyProvider' singleton (#47)

* .Make GraphQL execution strategies configurable by an `ExecutionStrategyProvider` singleton

* Removed repeated checks for executionStrategyProvider being null.

graphql-router/src/main/java/com/networknt/graphql/router/ExecutionStrategyProvider.java

@@ -0,0 +1,28 @@
+package com.networknt.graphql.router;
+
+import graphql.execution.ExecutionStrategy;
+
+/**
+ * ExecutionStrategyProvider interface that is used to inject execution strategy
+ * implementations into the framework. The service module will pass these on to
+ * the graphql-java framework.
+ *
+ * @author Logi Ragnarsson
+ */
+public interface ExecutionStrategyProvider {
+
+    /**
+     * Return an execution strategy to use for queries or null to use the default.
+     */
+    ExecutionStrategy getQueryExecutionStrategy();
+
+    /**
+     * Return an execution strategy to use for mutations or null to use the default.
+     */
+    ExecutionStrategy getMutationExecutionStrategy();
+
+    /**
+     * Return an execution strategy to use for subscriptions or null to use the default.
+     */
+    ExecutionStrategy getSubscriptionExecutionStrategy();
+}

graphql-router/src/main/java/com/networknt/graphql/router/handlers/GraphqlPostHandler.java

@@ -2,6 +2,7 @@
 
 import com.networknt.config.Config;
 import com.networknt.graphql.common.GraphqlUtil;
+import com.networknt.graphql.router.ExecutionStrategyProvider;
 import com.networknt.graphql.common.InstrumentationLoader;
 import com.networknt.graphql.common.InstrumentationProvider;
 import com.networknt.graphql.router.SchemaProvider;
@@ -10,6 +11,7 @@
 import graphql.ExecutionInput;
 import graphql.ExecutionResult;
 import graphql.GraphQL;
+import graphql.execution.ExecutionStrategy;
 import graphql.schema.GraphQLSchema;
 import io.undertow.server.HttpHandler;
 import io.undertow.server.HttpServerExchange;
@@ -37,6 +39,9 @@ public class GraphqlPostHandler implements HttpHandler {
 
     private static final Logger logger = LoggerFactory.getLogger(GraphqlPostHandler.class);
     static GraphQLSchema schema = null;
+    static ExecutionStrategy queryExecutionStrategy = null;
+    static ExecutionStrategy mutationExecutionStrategy = null;
+    static ExecutionStrategy subscriptionExecutionStrategy = null;
 
     static {
         // load GraphQL Schema with service loader. It should be defined in service.yml
@@ -48,6 +53,14 @@ public class GraphqlPostHandler implements HttpHandler {
             logger.error("Unable to load GraphQL schema - no SchemaProvider implementation in service.yml");
             throw new RuntimeException("Unable to load GraphQL schema - no SchemaProvider implementation in service.yml");
         }
+
+        // Replace default execution strategies if so configured.
+        ExecutionStrategyProvider executionStrategyProvider = SingletonServiceFactory.getBean(ExecutionStrategyProvider.class);
+        if(executionStrategyProvider != null) {
+            queryExecutionStrategy = executionStrategyProvider.getQueryExecutionStrategy();
+            mutationExecutionStrategy = executionStrategyProvider.getMutationExecutionStrategy();
+            subscriptionExecutionStrategy = executionStrategyProvider.getSubscriptionExecutionStrategy();
+        }
     }
 
     @Override
@@ -92,6 +105,15 @@ private GraphQL getGraphql() {
         if (InstrumentationLoader.graphqlInstrumentation != null) {
             graphql = graphql.instrumentation(InstrumentationLoader.graphqlInstrumentation);
         }
+        if(queryExecutionStrategy != null) {
+            graphql.queryExecutionStrategy(queryExecutionStrategy);
+        }
+        if(mutationExecutionStrategy != null) {
+            graphql.mutationExecutionStrategy(mutationExecutionStrategy);
+        }
+        if(subscriptionExecutionStrategy != null) {
+            graphql.subscriptionExecutionStrategy(subscriptionExecutionStrategy);
+        }
         return graphql.build();
     }
 }