diff --git a/gradle.properties b/gradle.properties
index ace86a27..404f8f90 100644
--- a/gradle.properties
+++ b/gradle.properties
@@ -7,9 +7,10 @@ PROJECT_LICENSE=MIT
 PROJECT_LICENSE_URL=https://github.com/graphql-java-kickstart/spring-boot-graphql/blob/master/LICENSE.md
 PROJECT_DEV_ID=apottere
 PROJECT_DEV_NAME=Andrew Potter
-LIB_GRAPHQL_JAVA_VER=17.2
+LIB_GRAPHQL_JAVA_VER=17.3
 LIB_JACKSON_VER=2.12.5
 LIB_SLF4J_VER=1.7.32
 LIB_LOMBOK_VER=1.18.20
 SOURCE_COMPATIBILITY=1.8
 TARGET_COMPATIBILITY=1.8
+GRADLE_WRAPPER_VER=7.0
diff --git a/graphql-java-servlet/build.gradle b/graphql-java-servlet/build.gradle
index 6f4e7019..f6cca231 100644
--- a/graphql-java-servlet/build.gradle
+++ b/graphql-java-servlet/build.gradle
@@ -31,12 +31,12 @@ dependencies {
     testImplementation 'io.github.graphql-java:graphql-java-annotations:8.3'
 
     // Unit testing
-    testImplementation "org.codehaus.groovy:groovy-all:3.0.8"
+    testImplementation "org.codehaus.groovy:groovy-all:3.0.9"
     testImplementation "org.spockframework:spock-core:2.0-groovy-3.0"
     testRuntimeOnly "cglib:cglib-nodep:3.3.0"
     testRuntimeOnly "org.objenesis:objenesis:3.2"
     testImplementation "org.slf4j:slf4j-simple:$LIB_SLF4J_VER"
-    testImplementation 'org.springframework:spring-test:5.3.9'
-    testRuntimeOnly 'org.springframework:spring-web:5.3.9'
+    testImplementation 'org.springframework:spring-test:5.3.10'
+    testRuntimeOnly 'org.springframework:spring-web:5.3.10'
     testImplementation 'com.google.guava:guava:30.1.1-jre'
 }
diff --git a/graphql-java-servlet/src/main/java/graphql/kickstart/servlet/HttpRequestInvokerImpl.java b/graphql-java-servlet/src/main/java/graphql/kickstart/servlet/HttpRequestInvokerImpl.java
index 9d10e398..829bf091 100644
--- a/graphql-java-servlet/src/main/java/graphql/kickstart/servlet/HttpRequestInvokerImpl.java
+++ b/graphql-java-servlet/src/main/java/graphql/kickstart/servlet/HttpRequestInvokerImpl.java
@@ -91,7 +91,10 @@ private CompletableFuture<Void> handle(
     return futureResult
         .thenApplyQueryResult()
         .thenAccept(
-            it -> writeResultResponse(futureResult.getInvocationInput(), it, request, response))
+            it -> {
+              listenerHandler.beforeFlush();
+              writeResultResponse(futureResult.getInvocationInput(), it, request, response);
+            })
         .thenAccept(it -> listenerHandler.onSuccess())
         .exceptionally(
             t ->
diff --git a/graphql-java-servlet/src/main/java/graphql/kickstart/servlet/ListenerHandler.java b/graphql-java-servlet/src/main/java/graphql/kickstart/servlet/ListenerHandler.java
index d9461002..faff966d 100644
--- a/graphql-java-servlet/src/main/java/graphql/kickstart/servlet/ListenerHandler.java
+++ b/graphql-java-servlet/src/main/java/graphql/kickstart/servlet/ListenerHandler.java
@@ -60,6 +60,10 @@ void runCallbacks(Consumer<RequestCallback> action) {
         });
   }
 
+  void beforeFlush() {
+    runCallbacks(it -> it.beforeFlush(request, response));
+  }
+
   void onSuccess() {
     runCallbacks(it -> it.onSuccess(request, response));
   }
diff --git a/graphql-java-servlet/src/main/java/graphql/kickstart/servlet/core/GraphQLServletListener.java b/graphql-java-servlet/src/main/java/graphql/kickstart/servlet/core/GraphQLServletListener.java
index 685d1faf..fc0feb34 100644
--- a/graphql-java-servlet/src/main/java/graphql/kickstart/servlet/core/GraphQLServletListener.java
+++ b/graphql-java-servlet/src/main/java/graphql/kickstart/servlet/core/GraphQLServletListener.java
@@ -6,17 +6,50 @@
 /** @author Andrew Potter */
 public interface GraphQLServletListener {
 
+  /**
+   * Called this method when the request started processing.
+   * @param request http request
+   * @param response http response
+   * @return request callback or {@literal null}
+   */
   default RequestCallback onRequest(HttpServletRequest request, HttpServletResponse response) {
     return null;
   }
 
+  /**
+   * The callback which used to add additional listeners for GraphQL request execution.
+   */
   interface RequestCallback {
 
+    /**
+     * Called right before the response will be written and flushed. Can be used for applying some
+     * changes to the response object, like adding response headers.
+     * @param request http request
+     * @param response http response
+     */
+    default void beforeFlush(HttpServletRequest request, HttpServletResponse response) {}
+
+    /**
+     * Called when GraphQL invoked successfully and the response was written already.
+     * @param request http request
+     * @param response http response
+     */
     default void onSuccess(HttpServletRequest request, HttpServletResponse response) {}
 
+    /**
+     * Called when GraphQL was failed and the response was written already.
+     * @param request http request
+     * @param response http response
+     */
     default void onError(
         HttpServletRequest request, HttpServletResponse response, Throwable throwable) {}
 
+    /**
+     * Called finally once on both success and failed GraphQL invocation. The response is also
+     * already written.
+     * @param request http request
+     * @param response http response
+     */
     default void onFinally(HttpServletRequest request, HttpServletResponse response) {}
   }
 }