GH-1065 Fix Collection discovery in JsonMapper

Resolves #1065

spring-cloud-function-context/src/main/java/org/springframework/cloud/function/json/JsonMapper.java

@@ -115,7 +115,7 @@ public abstract class JsonMapper {
 
 	public static boolean isJsonStringRepresentsCollection(Object value) {
 		boolean isJson = false;
-		if (value instanceof Iterable && !value.getClass().getPackage().getName().startsWith("reactor.util.function")) {
+		if (value instanceof Collection && !value.getClass().getPackage().getName().startsWith("reactor.util.function")) {
 			return true;
 		}
 		if (value instanceof byte[]) {

spring-cloud-function-context/src/test/java/org/springframework/cloud/function/utils/JsonMapperTests.java

@@ -20,7 +20,10 @@ import java.util.List;
 import java.util.stream.Stream;
 
 import com.fasterxml.jackson.databind.ObjectMapper;
+import com.fasterxml.jackson.databind.node.JsonNodeFactory;
+import com.fasterxml.jackson.databind.node.ObjectNode;
 import com.google.gson.Gson;
+import org.junit.jupiter.api.Test;
 import org.junit.jupiter.params.ParameterizedTest;
 import org.junit.jupiter.params.provider.MethodSource;
 
@@ -42,6 +45,28 @@ public class JsonMapperTests {
 		return Stream.of(new GsonMapper(new Gson()), new JacksonMapper(new ObjectMapper()));
 	}
 
+	@Test
+	public void objectNode_isJsonStringRepresentsCollection() {
+		ObjectNode node = JsonNodeFactory.instance.objectNode();
+		node.put("id", "1234ab");
+		node.put("foo", "bar");
+
+		/*
+		 * Passing the ObjectNode directly results in a positive identification as
+		 * a collection, as its distant parent JsonNode implements Iterable.
+		 */
+		assertThat(JsonMapper.isJsonStringRepresentsCollection(node)).isFalse();
+
+		String nodeAsString = node.toString();
+
+		/*
+		 * Sending the node as a string returns false, however, as the line
+		 * isJsonString(value) && str.startsWith("[") && str.endsWith("]")
+		 * will not be true.
+		 */
+		assertThat(JsonMapper.isJsonStringRepresentsCollection(nodeAsString)).isFalse();
+	}
+
 	@ParameterizedTest
 	@MethodSource("params")
 	public void vanillaArray(JsonMapper mapper) {