Add JacksonCollectors with toArrayNode() implementation (#4709)

Author: rikkarth

release-notes/CREDITS-2.x

@@ -1829,3 +1829,8 @@ Eduard Gomoliako (Gems@github)
 Mathijs Vogelzang (mathijs81@github)
  * Reported #4678: Java records don't serialize with `MapperFeature.REQUIRE_SETTERS_FOR_GETTERS`
   (2.18.0)
+
+Rikkarth (rikkarth@github)
+ * Contributed #4709: Add `JacksonCollectors` with `toArrayNode()` implementation
+  (2.18.0)
+

release-notes/VERSION-2.x

@@ -79,6 +79,8 @@ Project: jackson-databind
  (reported by @lnthai2002)
 #4699: Add extra `writeNumber()` method in `TokenBuffer`
  (contributed by @pjfanning)
+#4709: Add `JacksonCollectors` with `toArrayNode()` implementation
+ (contributed by @rikkarth)
 
 2.17.2 (05-Jul-2024)
 

src/main/java/com/fasterxml/jackson/databind/util/JacksonCollectors.java

@@ -0,0 +1,53 @@
+package com.fasterxml.jackson.databind.util;
+
+import java.util.stream.Collector;
+
+import com.fasterxml.jackson.databind.JsonNode;
+import com.fasterxml.jackson.databind.node.ArrayNode;
+import com.fasterxml.jackson.databind.node.JsonNodeCreator;
+import com.fasterxml.jackson.databind.node.JsonNodeFactory;
+
+/**
+ * Utility class that provides custom {@link Collector} implementations to support Stream operations.
+ * <p>
+ * This class is not meant to be instantiated and serves only as a utility class.
+ * </p>
+ *
+ * @since 2.18
+ */
+public abstract class JacksonCollectors {
+    /**
+     * Creates a {@link Collector} that collects {@link JsonNode} elements into an {@link ArrayNode}.
+     * <p>
+     * This method uses a {@link JsonNodeFactory} to create an empty {@link ArrayNode} and then adds each
+     * {@link JsonNode} to it.
+     * </p>
+     *<p>
+     * Short-cut to
+     *{@code toArrayNode(JsonNodeFactory.instance}}
+     *
+     * @return a {@link Collector} that collects {@link JsonNode} elements into an {@link ArrayNode}
+     */
+    public static Collector<JsonNode, ArrayNode, ArrayNode> toArrayNode() {
+        return toArrayNode(JsonNodeFactory.instance);
+    }
+
+    /**
+     * Creates a {@link Collector} that collects {@link JsonNode} elements into an {@link ArrayNode}.
+     * <p>
+     * This method uses a {@link JsonNodeFactory} to create an empty {@link ArrayNode} and then adds each
+     * {@link JsonNode} to it.
+     * </p>
+     *
+     * @param nodeCreator Factory for constructing {@link ArrayNode} to contain nodes in
+     *
+     * @return a {@link Collector} that collects {@link JsonNode} elements into an {@link ArrayNode}
+     */
+    public static Collector<JsonNode, ArrayNode, ArrayNode> toArrayNode(JsonNodeCreator nodeCreator) {
+        return Collector.of(
+                nodeCreator::arrayNode, // supplier
+                ArrayNode::add, // accumulator
+                ArrayNode::addAll // combiner
+            );
+    }
+}

src/test/java/com/fasterxml/jackson/databind/util/JacksonCollectorsTest.java

@@ -0,0 +1,33 @@
+package com.fasterxml.jackson.databind.util;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+
+import com.fasterxml.jackson.databind.JsonNode;
+import com.fasterxml.jackson.databind.ObjectMapper;
+import com.fasterxml.jackson.databind.node.ObjectNode;
+import java.util.stream.IntStream;
+import org.junit.jupiter.api.Test;
+
+public class JacksonCollectorsTest {
+
+    @Test
+    public void testToArrayNode()
+    {
+        final ObjectMapper objectMapper = new ObjectMapper();
+
+        final JsonNode jsonNodeResult = IntStream.range(0, 10)
+            .mapToObj(i -> {
+                ObjectNode objectNode = objectMapper.createObjectNode();
+                objectNode.put("testString", "example");
+                objectNode.put("testNumber", i);
+                objectNode.put("testBoolean", true);
+
+                return objectNode;
+            })
+            .collect(JacksonCollectors.toArrayNode());
+
+        assertEquals(10, jsonNodeResult.size());
+        jsonNodeResult.forEach(jsonNode -> assertFalse(jsonNode.isEmpty()));
+    }
+}