From 9eb09b03dbaaa0e3f544b0602df3107096cd8501 Mon Sep 17 00:00:00 2001
From: gobeomjun <theo@dwhale.kr>
Date: Wed, 12 Nov 2025 22:01:58 +0900
Subject: [PATCH] Optimize ArrayList allocations in
 BatchMessagingMessageConverter

Pre-size all ArrayList instances with batch size to eliminate
internal array resizing and reduce GC pressure in high-throughput
batch processing scenarios.

Fixes GH-4152

Signed-off-by: gobeomjun <theo@dwhale.kr>
---
 .../BatchMessagingMessageConverter.java       | 23 ++++++++++---------
 1 file changed, 12 insertions(+), 11 deletions(-)

diff --git a/spring-kafka/src/main/java/org/springframework/kafka/support/converter/BatchMessagingMessageConverter.java b/spring-kafka/src/main/java/org/springframework/kafka/support/converter/BatchMessagingMessageConverter.java
index ec37d82075..7b29b566c6 100644
--- a/spring-kafka/src/main/java/org/springframework/kafka/support/converter/BatchMessagingMessageConverter.java
+++ b/spring-kafka/src/main/java/org/springframework/kafka/support/converter/BatchMessagingMessageConverter.java
@@ -175,17 +175,18 @@ public Message<?> toMessage(List<ConsumerRecord<?, ?>> records, @Nullable Acknow
 				new KafkaMessageHeaders(this.generateMessageId, this.generateTimestamp);
 
 		Map<String, Object> rawHeaders = kafkaMessageHeaders.getRawHeaders();
-		List<Object> payloads = new ArrayList<>();
-		List<Object> keys = new ArrayList<>();
-		List<String> topics = new ArrayList<>();
-		List<Integer> partitions = new ArrayList<>();
-		List<Long> offsets = new ArrayList<>();
-		List<String> timestampTypes = new ArrayList<>();
-		List<Long> timestamps = new ArrayList<>();
-		List<Map<String, Object>> convertedHeaders = new ArrayList<>();
-		List<Headers> natives = new ArrayList<>();
-		List<ConsumerRecord<?, ?>> raws = new ArrayList<>();
-		List<ConversionException> conversionFailures = new ArrayList<>();
+		int batchSize = records.size();
+		List<Object> payloads = new ArrayList<>(batchSize);
+		List<Object> keys = new ArrayList<>(batchSize);
+		List<String> topics = new ArrayList<>(batchSize);
+		List<Integer> partitions = new ArrayList<>(batchSize);
+		List<Long> offsets = new ArrayList<>(batchSize);
+		List<String> timestampTypes = new ArrayList<>(batchSize);
+		List<Long> timestamps = new ArrayList<>(batchSize);
+		List<Map<String, Object>> convertedHeaders = new ArrayList<>(batchSize);
+		List<Headers> natives = new ArrayList<>(batchSize);
+		List<ConsumerRecord<?, ?>> raws = new ArrayList<>(batchSize);
+		List<ConversionException> conversionFailures = new ArrayList<>(batchSize);
 
 		addToRawHeaders(rawHeaders, convertedHeaders, natives, raws, conversionFailures);
 		commonHeaders(acknowledgment, consumer, rawHeaders, keys, topics, partitions, offsets, timestampTypes,