⚡ Bolt: HexFormat을 사용한 16진수 변환 최적화

.jules/bolt.md

@@ -0,0 +1,3 @@
+## 2024-05-15 - [Java Hex Conversion Optimization]
+**Learning:** Using `String.format("%02x", b)` in a loop to convert byte arrays to hex strings is a significant performance anti-pattern. It creates excessive string allocations and slows down operations. This is a common performance bottleneck specific to this codebase's architecture when generating hashes like SHA-256 for documents.
+**Action:** Replace `String.format` loops with Java 17+ `java.util.HexFormat.of().formatHex(bytes)`. This provides a more direct, allocation-efficient conversion. Keep this pattern in mind for any future byte manipulation or hashing implementations.

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) {