⚡ Bolt: HexFormat을 사용하여 헥스 문자열 변환 성능 최적화

.jules/bolt.md

@@ -0,0 +1,3 @@
+## 2026-07-02 - Java 21 HexFormat vs String.format Performance
+**Learning:** In Java 21 codebases, using `String.format("%02x", b)` inside a loop to convert a byte array to a hex string incurs significant memory allocation and execution time overhead.
+**Action:** Use `java.util.HexFormat.of().formatHex(bytes)` instead, which is optimized for byte array to hex string conversions without the overhead of manual looping and string formatting allocations.

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

@@ -419,15 +419,12 @@ private static String nullableClean(String value) {
         return cleaned.isEmpty() ? null : cleaned;
     }
 
-    private static String sha256Hex(byte[] bytes) {
+    private static String sha256Hex(final byte[] bytes) {
         try {
             MessageDigest digest = MessageDigest.getInstance("SHA-256");
             byte[] raw = digest.digest(bytes);
-            StringBuilder hex = new StringBuilder(raw.length * 2);
-            for (byte b : raw) {
-                hex.append(String.format("%02x", b));
-            }
-            return hex.toString();
+            // Bolt optimization: use HexFormat to avoid per-byte String.format allocations
+            return java.util.HexFormat.of().formatHex(raw);
         } catch (GeneralSecurityException ex) {
             throw new IllegalStateException("SHA-256 digest unavailable", ex);
         }

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

@@ -149,7 +149,7 @@ public RetryDeadLetterResult retryDeadLettered(UUID jobId, String operatorId) {
         return RetryDeadLetterResult.ACCEPTED;
     }
 
-    private String contentHash(MultipartFile file) {
+    private String contentHash(final MultipartFile file) {
         try (InputStream stream = file.getInputStream()) {
             MessageDigest digest = MessageDigest.getInstance("SHA-256");
             byte[] buffer = new byte[8192];
@@ -160,12 +160,8 @@ 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 optimization: use HexFormat to avoid per-byte String.format allocations
+            return java.util.HexFormat.of().formatHex(raw);
         } catch (NoSuchAlgorithmException ex) {
             throw new IllegalStateException("SHA-256 digest unavailable", ex);
         } catch (IOException ex) {

src/test/java/com/clearfolio/viewer/artifact/ArtifactLinkServiceHexFormatTest.java

@@ -0,0 +1,19 @@
+package com.clearfolio.viewer.artifact;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import java.nio.charset.StandardCharsets;
+import java.security.MessageDigest;
+import java.util.HexFormat;
+
+import org.junit.jupiter.api.Test;
+
+public class ArtifactLinkServiceHexFormatTest {
+    @Test
+    public void testSha256HexEncoding() throws Exception {
+        byte[] input = "abc".getBytes(StandardCharsets.UTF_8);
+        String hex = HexFormat.of().formatHex(MessageDigest.getInstance("SHA-256").digest(input));
+        assertEquals("ba7816bf8f01cfea414140de5dae2223b00361a396177a9cb410ff61f20015ad", hex);
+        assertEquals(64, hex.length());
+    }
+}

src/test/java/com/clearfolio/viewer/service/DefaultDocumentConversionServiceHexFormatTest.java

@@ -0,0 +1,19 @@
+package com.clearfolio.viewer.service;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import java.nio.charset.StandardCharsets;
+import java.security.MessageDigest;
+import java.util.HexFormat;
+
+import org.junit.jupiter.api.Test;
+
+public class DefaultDocumentConversionServiceHexFormatTest {
+    @Test
+    public void testContentHashHexEncoding() throws Exception {
+        byte[] input = "abc".getBytes(StandardCharsets.UTF_8);
+        String hex = HexFormat.of().formatHex(MessageDigest.getInstance("SHA-256").digest(input));
+        assertEquals("ba7816bf8f01cfea414140de5dae2223b00361a396177a9cb410ff61f20015ad", hex);
+        assertEquals(64, hex.length());
+    }
+}