From c30aa276f8ce41125dbf10726489a5d5be031e78 Mon Sep 17 00:00:00 2001
From: seonghobae <8172694+seonghobae@users.noreply.github.com>
Date: Mon, 6 Jul 2026 21:20:56 +0000
Subject: [PATCH] =?UTF-8?q?=E2=9A=A1=20Bolt:=20String.format=EC=9D=84=20He?=
 =?UTF-8?q?xFormat=EC=9C=BC=EB=A1=9C=20=EB=B3=80=EA=B2=BD=ED=95=98?=
 =?UTF-8?q?=EC=97=AC=20=EC=84=B1=EB=8A=A5=20=EC=B5=9C=EC=A0=81=ED=99=94?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

반복문 내에서 `String.format`을 사용하여 16진수 문자열을 생성하는 것은 구문 분석 및 중간 객체 생성으로 인해 성능 저하를 유발합니다. 이를 Java 17+의 표준인 불변 및 스레드 안전 `java.util.HexFormat`을 사용하도록 변경하여 성능을 최적화하고 중간 객체 할당을 제거했습니다.

영향:
- `DefaultDocumentConversionService.contentHash()` 및 `ArtifactLinkService.sha256Hex()`에서 문자열 생성 비용 감소
- 객체 생성 감소 및 불필요한 가비지 컬렉터 부하 방지
---
 .jules/bolt.md                                           | 3 +++
 .../clearfolio/viewer/artifact/ArtifactLinkService.java  | 8 +++-----
 .../viewer/service/DefaultDocumentConversionService.java | 9 +++------
 3 files changed, 9 insertions(+), 11 deletions(-)
 create mode 100644 .jules/bolt.md

diff --git a/.jules/bolt.md b/.jules/bolt.md
new file mode 100644
index 00000000..108b134f
--- /dev/null
+++ b/.jules/bolt.md
@@ -0,0 +1,3 @@
+## 2026-07-02 - String.format in loops
+**Learning:** `String.format` is slow for hex conversion inside loops.
+**Action:** Replace it with `HexFormat.of().formatHex(bytes)` which is significantly faster and doesn't do intermediate string creations.
diff --git a/src/main/java/com/clearfolio/viewer/artifact/ArtifactLinkService.java b/src/main/java/com/clearfolio/viewer/artifact/ArtifactLinkService.java
index 454b0448..33e5fe4e 100644
--- a/src/main/java/com/clearfolio/viewer/artifact/ArtifactLinkService.java
+++ b/src/main/java/com/clearfolio/viewer/artifact/ArtifactLinkService.java
@@ -38,6 +38,8 @@
 @Service
 public class ArtifactLinkService {
 
+    private static final java.util.HexFormat HEX_FORMAT = java.util.HexFormat.of();
+
     /**
      * Query parameter used by PDF.js-compatible artifact URLs.
      */
@@ -423,11 +425,7 @@ private static String sha256Hex(byte[] bytes) {
         try {
             MessageDigest digest = MessageDigest.getInstance("SHA-256");
             byte[] raw = digest.digest(bytes);
-            StringBuilder hex = new StringBuilder(raw.length * 2);
-            for (byte b : raw) {
-                hex.append(String.format("%02x", b));
-            }
-            return hex.toString();
+            return HEX_FORMAT.formatHex(raw);
         } catch (GeneralSecurityException ex) {
             throw new IllegalStateException("SHA-256 digest unavailable", ex);
         }
diff --git a/src/main/java/com/clearfolio/viewer/service/DefaultDocumentConversionService.java b/src/main/java/com/clearfolio/viewer/service/DefaultDocumentConversionService.java
index b8787f35..7ef568b5 100644
--- a/src/main/java/com/clearfolio/viewer/service/DefaultDocumentConversionService.java
+++ b/src/main/java/com/clearfolio/viewer/service/DefaultDocumentConversionService.java
@@ -26,6 +26,8 @@
 @Service
 public class DefaultDocumentConversionService implements DocumentConversionService {
 
+    private static final java.util.HexFormat HEX_FORMAT = java.util.HexFormat.of();
+
     private final ConversionJobRepository repository;
     private final ConversionJobStateStore stateStore;
     private final DocumentValidationService validationService;
@@ -160,12 +162,7 @@ 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 HEX_FORMAT.formatHex(raw);
         } catch (NoSuchAlgorithmException ex) {
             throw new IllegalStateException("SHA-256 digest unavailable", ex);
         } catch (IOException ex) {