⚡ Bolt: 성능 향상을 위한 재사용 가능한 HexFormat 적용

.jules/bolt.md

@@ -1,3 +1,6 @@
+## 2026-07-09 - Reuse HexFormat instance to reduce allocations and loops
+**Learning:** Using `String.format("%02x", b)` in a loop or calling `HexFormat.of()` repeatedly for hex conversions creates unnecessary intermediate object allocations and reduces performance.
+**Action:** Always use a single, reusable `private static final java.util.HexFormat HEX_FORMAT = java.util.HexFormat.of();` instance and its `formatHex` method for byte-to-hex string conversions.
 ## 2026-07-09 - 16진수 문자열 변환 성능 최적화
 **Learning:** 루프 내에서 `String.format("%02x", b)`를 사용하는 것은 지속적인 객체 할당과 파싱으로 인해 Java에서 매우 비효율적입니다. Java 17 이상에서는 이 사용 사례에 최적화된 `java.util.HexFormat`을 제공합니다.
 **Action:** 바이트 배열을 16진수 문자열로 변환할 때 성능을 향상시키고 메모리 할당을 줄이기 위해 `java.util.HexFormat.of().formatHex(bytes)`를 사용해야 합니다.

src/main/java/com/clearfolio/viewer/artifact/ArtifactLinkService.java

@@ -10,6 +10,7 @@
 import java.time.Instant;
 import java.util.Arrays;
 import java.util.Base64;
+import java.util.HexFormat;
 import java.util.List;
 import java.util.Optional;
 import java.util.UUID;
@@ -39,6 +40,8 @@
 @Service
 public class ArtifactLinkService {
 
+    private static final HexFormat HEX_FORMAT = HexFormat.of();
+
     /**
      * Query parameter used by PDF.js-compatible artifact URLs.
      */
@@ -426,9 +429,8 @@ private static String sha256Hex(byte[] bytes) {
         try {
             MessageDigest digest = MessageDigest.getInstance("SHA-256");
             byte[] raw = digest.digest(bytes);
-            // Optimization: java.util.HexFormat.of().formatHex() is faster
-            // and allocates less memory than String.format.
-            return java.util.HexFormat.of().formatHex(raw);
+            // Reused HexFormat for performance
+            return HEX_FORMAT.formatHex(raw);
         } catch (GeneralSecurityException ex) {
             throw new IllegalStateException("SHA-256 digest unavailable", ex);
         }

src/main/java/com/clearfolio/viewer/service/DefaultDocumentConversionService.java

@@ -4,6 +4,7 @@
 import java.io.InputStream;
 import java.security.MessageDigest;
 import java.security.NoSuchAlgorithmException;
+import java.util.HexFormat;
 import java.util.Locale;
 import java.util.Optional;
 import java.util.UUID;
@@ -33,12 +34,12 @@
 @Service
 public class DefaultDocumentConversionService implements DocumentConversionService {
 
+    private static final HexFormat HEX_FORMAT = HexFormat.of();
     private static final org.slf4j.Logger log = org.slf4j.LoggerFactory.getLogger(
             DefaultDocumentConversionService.class);
     private static final String PDF_CONTENT_TYPE = "application/pdf";
     private static final String PDF_EXTENSION_SUFFIX = ".pdf";
     private static final byte[] PDF_MAGIC_HEADER = {'%', 'P', 'D', 'F', '-'};
-
     private final ConversionJobRepository repository;
     private final ConversionJobStateStore stateStore;
     private final DocumentValidationService validationService;
@@ -331,9 +332,8 @@ private String contentHash(MultipartFile file) {
             }
 
             byte[] raw = digest.digest();
-            // Optimization: java.util.HexFormat.of().formatHex() is faster
-            // and allocates less memory than String.format.
-            return java.util.HexFormat.of().formatHex(raw);
+            // Reused HexFormat for performance
+            return HEX_FORMAT.formatHex(raw);
         } catch (NoSuchAlgorithmException ex) {
             throw new IllegalStateException("SHA-256 digest unavailable", ex);
         } catch (IOException ex) {

src/main/java/com/clearfolio/viewer/service/DefaultDocumentValidationService.java

@@ -25,6 +25,7 @@
 @Service
 public class DefaultDocumentValidationService implements DocumentValidationService {
 
+    private static final HexFormat HEX_FORMAT = HexFormat.of();
     private static final Logger LOGGER = LoggerFactory.getLogger(DefaultDocumentValidationService.class);
     private static final int FINGERPRINT_TRUNCATE_BYTES = 8;
 
@@ -201,7 +202,8 @@ private String tokenFingerprint(String approvalToken) {
         try {
             MessageDigest digest = MessageDigest.getInstance("SHA-256");
             byte[] hashed = digest.digest(approvalToken.getBytes(StandardCharsets.UTF_8));
-            return HexFormat.of().formatHex(hashed, 0, FINGERPRINT_TRUNCATE_BYTES);
+            // Reused HexFormat for performance
+            return HEX_FORMAT.formatHex(hashed, 0, FINGERPRINT_TRUNCATE_BYTES);
         } catch (NoSuchAlgorithmException ex) {
             throw new IllegalStateException("SHA-256 digest unavailable", ex);
         }