⚡ Bolt: String.format을 HexFormat으로 변경하여 해시 변환 성능 최적화

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;
@@ -22,6 +23,8 @@
 @Service
 public class DefaultDocumentConversionService implements DocumentConversionService {
 
+    private static final HexFormat HEX_FORMAT = HexFormat.of();
+
     private final ConversionJobRepository repository;
     private final DocumentValidationService validationService;
     private final ConversionWorker conversionWorker;
@@ -121,12 +124,7 @@ 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 HEX_FORMAT.formatHex(raw);
         } catch (NoSuchAlgorithmException ex) {
             throw new IllegalStateException("SHA-256 digest unavailable", ex);
         } catch (IOException ex) {

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

@@ -174,6 +174,34 @@ void returnsDifferentJobIdsForDifferentPayloads() {
         assertEquals(2, worker.enqueuedCount());
     }
 
+    @Test
+    void storesContentHashAsLowercaseSha256Hex() {
+        ConversionJobRepository repository = new InMemoryConversionJobRepository();
+        RecordingConversionWorker worker = new RecordingConversionWorker();
+        DocumentConversionService service = new DefaultDocumentConversionService(
+                repository,
+                new DefaultDocumentValidationService(new ConversionProperties()),
+                worker,
+                new ConversionProperties()
+        );
+
+        byte[] payload = "hello-viewer".getBytes(StandardCharsets.UTF_8);
+        MockMultipartFile file = new MockMultipartFile(
+                "file",
+                "contract.docx",
+                "application/octet-stream",
+                payload
+        );
+
+        UUID jobId = service.submit(file);
+
+        ConversionJob job = repository.findById(jobId).orElseThrow();
+        assertEquals(
+                "6908f2d58e1a44cd5f7fcc1c76a2a14e801e9158779d569466b4471ae4aae75d",
+                job.getContentHash()
+        );
+    }
+
     @Test
     void returnsSameJobForConcurrentDuplicatePayloads() throws Exception {
         ConversionJobRepository repository = new InMemoryConversionJobRepository();