From 27a34bc9593c68e7bcdb61ac76f2aeb6b74490d6 Mon Sep 17 00:00:00 2001
From: seonghobae <8172694+seonghobae@users.noreply.github.com>
Date: Wed, 1 Jul 2026 20:53:22 +0000
Subject: [PATCH] =?UTF-8?q?=E2=9A=A1=20Bolt:=20Byte=20=EB=B0=B0=EC=97=B4?=
 =?UTF-8?q?=20=ED=97=A5=EC=8A=A4=20=EB=AC=B8=EC=9E=90=EC=97=B4=20=EB=B3=80?=
 =?UTF-8?q?=ED=99=98=20=EC=84=B1=EB=8A=A5=20=EC=B5=9C=EC=A0=81=ED=99=94=20?=
 =?UTF-8?q?(HexFormat=20=EC=A0=81=EC=9A=A9)?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 .jules/bolt.md                                            | 3 +++
 .../viewer/service/DefaultDocumentConversionService.java  | 8 +++-----
 2 files changed, 6 insertions(+), 5 deletions(-)
 create mode 100644 .jules/bolt.md

diff --git a/.jules/bolt.md b/.jules/bolt.md
new file mode 100644
index 0000000..4168133
--- /dev/null
+++ b/.jules/bolt.md
@@ -0,0 +1,3 @@
+## 2026-07-01 - Byte Array to Hex String Conversion Optimization
+**Learning:** In Java 21, using `String.format("%02x", b)` inside a loop to convert a byte array to a hex string causes unnecessary allocations and is significantly slower than native alternatives.
+**Action:** Use `java.util.HexFormat.of().formatHex(bytes)` for faster and allocation-free conversions from byte arrays to hex strings in this codebase.
diff --git a/src/main/java/com/clearfolio/viewer/service/DefaultDocumentConversionService.java b/src/main/java/com/clearfolio/viewer/service/DefaultDocumentConversionService.java
index 9c59593..c0335f9 100644
--- a/src/main/java/com/clearfolio/viewer/service/DefaultDocumentConversionService.java
+++ b/src/main/java/com/clearfolio/viewer/service/DefaultDocumentConversionService.java
@@ -121,12 +121,10 @@ 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();
+            // Bolt Performance Optimization:
+            // Use HexFormat instead of String.format loop for performance.
+            return java.util.HexFormat.of().formatHex(raw);
         } catch (NoSuchAlgorithmException ex) {
             throw new IllegalStateException("SHA-256 digest unavailable", ex);
         } catch (IOException ex) {