From d39ff37299e8abf521795454cb6e9f815f725c87 Mon Sep 17 00:00:00 2001
From: seonghobae <8172694+seonghobae@users.noreply.github.com>
Date: Tue, 30 Jun 2026 21:18:43 +0000
Subject: [PATCH] =?UTF-8?q?=E2=9A=A1=20Bolt:=20=EB=B0=94=EC=9D=B4=ED=8A=B8?=
 =?UTF-8?q?=20=EB=B0=B0=EC=97=B4=EC=9D=84=2016=EC=A7=84=EC=88=98=20?=
 =?UTF-8?q?=EB=AC=B8=EC=9E=90=EC=97=B4=EB=A1=9C=20=EB=B3=80=ED=99=98?=
 =?UTF-8?q?=ED=95=A0=20=EB=95=8C=20=EC=84=B1=EB=8A=A5=20=EA=B0=9C=EC=84=A0?=
 =?UTF-8?q?=EC=9D=84=20=EC=9C=84=ED=95=B4=20HexFormat=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, 5 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..2bcd17d
--- /dev/null
+++ b/.jules/bolt.md
@@ -0,0 +1,3 @@
+## 2024-06-30 - Hex Format Optimization
+**Learning:** Using String.format() in a loop to convert byte arrays to hex strings allocates many temporary objects (String, Object[] for varargs) and performs poorly. The application's DefaultDocumentConversionService previously used this pattern for hashing uploads, impacting memory and CPU heavily.
+**Action:** Always prefer java.util.HexFormat.of().formatHex(bytes) introduced in Java 17 for byte-to-hex conversion to improve performance, minimize object allocation, and make the code cleaner.
diff --git a/src/main/java/com/clearfolio/viewer/service/DefaultDocumentConversionService.java b/src/main/java/com/clearfolio/viewer/service/DefaultDocumentConversionService.java
index 9c59593..92e76a5 100644
--- a/src/main/java/com/clearfolio/viewer/service/DefaultDocumentConversionService.java
+++ b/src/main/java/com/clearfolio/viewer/service/DefaultDocumentConversionService.java
@@ -7,6 +7,7 @@
 import java.io.InputStream;
 import java.security.MessageDigest;
 import java.security.NoSuchAlgorithmException;
+import java.util.HexFormat;
 
 import org.springframework.stereotype.Service;
 import org.springframework.web.multipart.MultipartFile;
@@ -121,12 +122,7 @@ 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 HexFormat.of().formatHex(raw);
         } catch (NoSuchAlgorithmException ex) {
             throw new IllegalStateException("SHA-256 digest unavailable", ex);
         } catch (IOException ex) {