Allows to defines a getInstance() method on TypeResolver/DataFetcher/Validators/DefaultValues..

Author: Thomas Draier

src/main/java/graphql/annotations/processor/util/ReflectionKit.java

@@ -18,6 +18,8 @@
 
 import java.lang.reflect.Constructor;
 import java.lang.reflect.InvocationTargetException;
+import java.lang.reflect.Method;
+import java.lang.reflect.Modifier;
 
 /**
  * A package level helper in calling reflective methods and turning them into
@@ -26,8 +28,16 @@
 public class ReflectionKit {
     public static <T> T newInstance(Class<T> clazz) throws GraphQLAnnotationsException {
         try {
+            try {
+                Method getInstance = clazz.getMethod("getInstance", new Class<?>[0]);
+                if (Modifier.isStatic(getInstance.getModifiers()) && clazz.isAssignableFrom(getInstance.getReturnType())) {
+                    return (T) getInstance.invoke(null);
+                }
+            } catch (NoSuchMethodException e) {
+                // ignore, just call the constructor
+            }
             return clazz.newInstance();
-        } catch (InstantiationException | IllegalAccessException e) {
+        } catch (InstantiationException | InvocationTargetException | IllegalAccessException e) {
             throw new GraphQLAnnotationsException("Unable to instantiate class : " + clazz, e);
         }
     }

src/test/java/graphql/annotations/GraphQLInterfaceTest.java

@@ -69,6 +69,10 @@ public void noResolver() {
 
     public static class Resolver implements TypeResolver {
 
+        public static Resolver getInstance() {
+            return new Resolver();
+        }
+
         @Override
         public GraphQLObjectType getType(TypeResolutionEnvironment env) {
             try {