Make applyPatch a generic method

src/main/java/ch/dlmw/swisssignchallenge/controllers/SigningRequestDocumentController.java

@@ -26,13 +26,7 @@ public class SigningRequestDocumentController implements SigningRequestDocumentA
         var document = signingRequestDocumentService.getSigningRequestDocument(id);
 
         try {
-            JsonNode patchNode = objectMapper.valueToTree(patchOperations);
+            var patchedDocument = applyPatch(patchOperations, document, SigningRequestDocument.class);
-
-            JsonPatch jsonPatch = JsonPatch.fromJson(patchNode);
-
-            JsonNode patchedNode = jsonPatch.apply(objectMapper.convertValue(document, JsonNode.class));
-
-            SigningRequestDocument patchedDocument = objectMapper.treeToValue(patchedNode, SigningRequestDocument.class);
 
             signingRequestDocumentService.updateSigningRequestDocument(patchedDocument);
 
@@ -44,4 +38,14 @@ public class SigningRequestDocumentController implements SigningRequestDocumentA
         }
     }
 
+    private <T> T applyPatch(List<PatchOperation> patchOperations, T object, Class<T> entityType) throws JsonPatchException, IOException {
+        JsonNode patchNode = objectMapper.valueToTree(patchOperations);
+        JsonPatch jsonPatch = JsonPatch.fromJson(patchNode);
+
+        // Convert the entity to JsonNode and apply the patch
+        JsonNode entityNode = objectMapper.convertValue(object, JsonNode.class);
+        JsonNode patchedNode = jsonPatch.apply(entityNode);
+
+        return objectMapper.treeToValue(patchedNode, entityType);
+    }
 }