Document concrete types for batch trigger metadata

README.md

@@ -226,6 +226,11 @@ public class Function {
 }
 ```
 
+For trigger metadata containing a batch of values, use a concrete array or collection type that
+matches the metadata. For example, a Kafka trigger with `cardinality = Cardinality.MANY` can bind
+topics as `@BindingName("TopicArray") String[] topics` and offsets as
+`@BindingName("OffsetArray") long[] offsets`. `Object[]` is not supported for collection metadata.
+
 ### License
 
 This project is under the benevolent umbrella of the [.NET Foundation](http://www.dotnetfoundation.org/) and is licensed under the MIT License.

src/main/java/com/microsoft/azure/functions/annotation/BindingName.java

@@ -18,6 +18,14 @@
  * bindings in function.json manually.
  * </p>
  *
+ * <p>
+ * For batch trigger metadata, use an array or collection whose element type matches the metadata
+ * value. For example, Kafka metadata can be bound with
+ * {@code @BindingName("TopicArray") String[] topics} and
+ * {@code @BindingName("OffsetArray") long[] offsets}. {@code Object[]} is not supported for
+ * collection metadata.
+ * </p>
+ *
  * @since 1.0.0
  */
 @Target(ElementType.PARAMETER)