From bd3291a8a669e25a61c99a4cd91fc7a87dc87f9b Mon Sep 17 00:00:00 2001
From: seonghobae <8172694+seonghobae@users.noreply.github.com>
Date: Tue, 30 Jun 2026 06:28:29 +0000
Subject: [PATCH] =?UTF-8?q?=E2=9A=A1=20Bolt:=20[=EC=84=B1=EB=8A=A5=20?=
 =?UTF-8?q?=EA=B0=9C=EC=84=A0]=20String.format=20=EA=B8=B0=EB=B0=98=20hex?=
 =?UTF-8?q?=20=EB=B3=80=ED=99=98=EC=9D=84=20HexFormat.of().formatHex()?=
 =?UTF-8?q?=EB=A1=9C=20=EB=8C=80=EC=B2=B4?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

DefaultDocumentConversionService.java에서 byte array를 hex string으로 변환하는 과정의 성능 병목을 해결합니다.
루프 내에서 String.format("%02x", b)를 반복 호출하는 방식은 많은 메모리 할당과 오버헤드를 발생시킵니다.
이를 Java 내장 API인 java.util.HexFormat.of().formatHex(raw)를 사용하도록 변경하여 처리 속도를 높이고 메모리 사용량을 줄입니다.

관련 학습 내용은 .jules/bolt.md 에 기록하였습니다.
---
 .jules/bolt.md                                             | 3 +++
 .../viewer/service/DefaultDocumentConversionService.java   | 7 +------
 2 files changed, 4 insertions(+), 6 deletions(-)
 create mode 100644 .jules/bolt.md

diff --git a/.jules/bolt.md b/.jules/bolt.md
new file mode 100644
index 0000000..b9c5f72
--- /dev/null
+++ b/.jules/bolt.md
@@ -0,0 +1,3 @@
+## 2024-06-30 - Replace String.format with HexFormat for byte-to-hex conversion
+**Learning:** Using a loop with `String.format("%02x", b)` to convert byte arrays to hex strings causes unnecessary memory allocations and is a performance bottleneck in this application.
+**Action:** Always use `java.util.HexFormat.of().formatHex(bytes)` instead of manual string formatting loops for converting bytes to hex strings to optimize performance and memory usage.
diff --git a/src/main/java/com/clearfolio/viewer/service/DefaultDocumentConversionService.java b/src/main/java/com/clearfolio/viewer/service/DefaultDocumentConversionService.java
index 9c59593..3cd4597 100644
--- a/src/main/java/com/clearfolio/viewer/service/DefaultDocumentConversionService.java
+++ b/src/main/java/com/clearfolio/viewer/service/DefaultDocumentConversionService.java
@@ -121,12 +121,7 @@ private String contentHash(MultipartFile file) {
             }
 
             byte[] raw = digest.digest();
-            StringBuilder hex = new StringBuilder(raw.length * 2);
-            for (byte b : raw) {
-                hex.append(String.format("%02x", b));
-            }
-
-            return hex.toString();
+            return java.util.HexFormat.of().formatHex(raw);
         } catch (NoSuchAlgorithmException ex) {
             throw new IllegalStateException("SHA-256 digest unavailable", ex);
         } catch (IOException ex) {