refactor(testcontainers): extract ObjectMapper to static field in tdg.Utils

ObjectMapper instances are thread-safe after configuration and can be
safely reused. Hoisting the instance to a static final field removes
the duplicated `new ObjectMapper()` allocations in sendUsers() and
getUsers() and avoids creating a fresh mapper (and re-reading its
configuration) on every call.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Author: dkasimovskiy

CHANGELOG.md

@@ -13,6 +13,7 @@
   surface into a single parameterized suite.
 - Add constructor/builder parameters to supply the initial Lua script as a string or as a file path, and optional additional script paths copied into the container data directory (`Tarantool2Container`, `CartridgeClusterContainer`, `VshardClusterContainer`); simplify bundled `server.lua` accordingly.
 - Upgrade TQE to v3.5.0.
+- Extract `ObjectMapper` to a static field in the test `tdg.Utils` helper to avoid recreating it on every `sendUsers`/`getUsers` call.
 
 ### Documentation
 

testcontainers/src/test/java/org/testcontainers/containers/tdg/Utils.java

@@ -25,15 +25,16 @@
 
 public abstract class Utils {
 
+  private static final ObjectMapper OBJECT_MAPPER = new ObjectMapper();
+
   private Utils() {}
 
   public static List<User> sendUsers(List<User> users, TDGContainer<?> container)
       throws IOException {
     final List<User> result = new ArrayList<>();
-    final ObjectMapper objectMapper = new ObjectMapper();
     try (CloseableHttpClient httpClient = HttpClients.createDefault()) {
       for (final User user : users) {
-        final String jsonUser = objectMapper.writeValueAsString(user);
+        final String jsonUser = OBJECT_MAPPER.writeValueAsString(user);
         final String address = HttpHost.unsecure(container.httpMappedAddress()) + "/data/User";
         final HttpPost post = new HttpPost(address);
         final HttpEntity entity = new StringEntity(jsonUser, ContentType.APPLICATION_JSON);
@@ -50,7 +51,7 @@ public static List<User> sendUsers(List<User> users, TDGContainer<?> container)
                             + ", "
                             + response.getReasonPhrase());
                   }
-                  return objectMapper.readValue(
+                  return OBJECT_MAPPER.readValue(
                       EntityUtils.toString(response.getEntity()), User.class);
                 }));
       }
@@ -59,7 +60,6 @@ public static List<User> sendUsers(List<User> users, TDGContainer<?> container)
   }
 
   public static List<User> getUsers(int count, TDGContainer<?> node) throws IOException {
-    final ObjectMapper objectMapper = new ObjectMapper();
     try (CloseableHttpClient httpClient = HttpClients.createDefault()) {
       final String address =
           HttpHost.unsecure(node.httpMappedAddress()) + "/data/User?first=" + count;
@@ -73,7 +73,7 @@ public static List<User> getUsers(int count, TDGContainer<?> node) throws IOExce
                       + ", "
                       + response.getReasonPhrase());
             }
-            return objectMapper.readValue(
+            return OBJECT_MAPPER.readValue(
                 EntityUtils.toString(response.getEntity()), new TypeReference<List<User>>() {});
           });
     }