⚡ Bolt: [성능 개선] String.format 기반 hex 변환을 HexFormat.of().formatHex()로 대체

.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.

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) {