Support context parameters in @BatchMapping methods

Closes gh-172

spring-graphql-docs/src/docs/asciidoc/index.adoc

@@ -927,10 +927,11 @@ the simple class name of the input `List` element type. Both can be customized t
 annotation attributes. The type name can also be inherited from a class level
 `@SchemaMapping`.
 
+
 [[controllers-batch-mapping-signature]]
 ==== Method Signature
 
-Batch mapping methods support two types of arguments:
+Batch mapping methods support the following arguments:
 
 [cols="1,2"]
 |===
@@ -942,10 +943,19 @@ Batch mapping methods support two types of arguments:
 | `java.security.Principal`
 | Obtained from Spring Security context, if available.
 
+| `@ContextValue`
+| For access to a value from the `GraphQLContext` of `BatchLoaderEnvironment`,
+  which is the same context as the one from the `DataFetchingEnvironment`.
+
+| `GraphQLContext`
+| For access to the context from the `BatchLoaderEnvironment`,
+  which is the same context as the one from the `DataFetchingEnvironment`.
+
 | `BatchLoaderEnvironment`
 | The environment that is available in GraphQL Java to a
 `org.dataloader.BatchLoaderWithContext`.
 
+
 |===
 
 Batch mapping methods can return:

spring-graphql/src/main/java/org/springframework/graphql/data/method/annotation/support/BatchLoaderHandlerMethod.java

@@ -20,6 +20,7 @@ import java.util.Arrays;
 import java.util.Collection;
 import java.util.Map;
 
+import graphql.GraphQLContext;
 import org.dataloader.BatchLoaderEnvironment;
 import reactor.core.publisher.Flux;
 import reactor.core.publisher.Mono;
@@ -28,6 +29,7 @@ import org.springframework.core.CollectionFactory;
 import org.springframework.core.MethodParameter;
 import org.springframework.graphql.data.method.HandlerMethod;
 import org.springframework.graphql.data.method.InvocableHandlerMethodSupport;
+import org.springframework.graphql.data.method.annotation.ContextValue;
 import org.springframework.lang.Nullable;
 import org.springframework.util.ClassUtils;
 
@@ -119,6 +121,12 @@ public class BatchLoaderHandlerMethod extends InvocableHandlerMethodSupport {
 			collection.addAll(keys);
 			return collection;
 		}
+		else if (parameter.hasParameterAnnotation(ContextValue.class)) {
+			return ContextValueMethodArgumentResolver.resolveContextValue(parameter, null, environment.getContext());
+		}
+		else if (parameterType.equals(GraphQLContext.class)) {
+			return environment.getContext();
+		}
 		else if (parameterType.isInstance(environment)) {
 			return environment;
 		}

spring-graphql/src/main/java/org/springframework/graphql/data/method/annotation/support/ContextValueMethodArgumentResolver.java

@@ -52,7 +52,7 @@ public class ContextValueMethodArgumentResolver implements HandlerMethodArgument
 	}
 
 	@Nullable
-	private Object resolveContextValue(
+	static Object resolveContextValue(
 			MethodParameter parameter, @Nullable Object localContext, GraphQLContext graphQlContext) {
 
 		ContextValue annotation = parameter.getParameterAnnotation(ContextValue.class);
@@ -78,7 +78,7 @@ public class ContextValueMethodArgumentResolver implements HandlerMethodArgument
 		return wrapAsOptionalIfNecessary(value, parameterType);
 	}
 
-	private String getValueName(MethodParameter parameter, ContextValue annotation) {
+	private static String getValueName(MethodParameter parameter, ContextValue annotation) {
 		if (StringUtils.hasText(annotation.name())) {
 			return annotation.name();
 		}
@@ -92,7 +92,7 @@ public class ContextValueMethodArgumentResolver implements HandlerMethodArgument
 	}
 
 	@Nullable
-	private Object wrapAsOptionalIfNecessary(@Nullable Object value, Class<?> type) {
+	private static Object wrapAsOptionalIfNecessary(@Nullable Object value, Class<?> type) {
 		return (type.equals(Optional.class) ? Optional.ofNullable(value) : value);
 	}