provectus/kafka-ui · error · ValidationException

Multiple serdes with same name

Error message

Multiple serdes with same name: ${serdeConfig.getName()}

What it means

SerdesInitializer registers serdes into a name-keyed map and rejects duplicates. Two serde entries with the same name within one cluster are ambiguous (name is the lookup key), so the second occurrence throws ValidationException('Multiple serdes with same name: <name>').

Solutions

  1. Rename one of the duplicate serde entries to a unique name
  2. Remove the redundant duplicate entry from the config
  3. Check for duplicated blocks introduced by config merge/override

Example fix

// before
serde:
  - name: my-serde
    className: com.example.MySerde
  - name: my-serde
    className: com.example.OtherSerde
// after
serde:
  - name: my-serde
    className: com.example.MySerde
  - name: other-serde
    className: com.example.OtherSerde
Defensive patterns

Strategy: validation

Validate before calling

Set<String> seen = new HashSet<>();
for (SerdeConfig s : clusterProperties.getSerde()) {
  if (!seen.add(s.getName()))
    throw new IllegalArgumentException("Duplicate serde name: " + s.getName());
}

Try / catch

try {
  serdes = initializer.init(...);
} catch (ValidationException e) {
  log.error("Duplicate serde names: {}", e.getMessage());
  throw e;
}

Prevention

When it happens

Trigger: Two entries under kafka.clusters.<n>.serde share the same 'name' value; init fails when the second one is processed.

Common situations: Copy-pasting a serde block and forgetting to change the name; YAML list accidentally containing the same entry twice after a merge conflict resolution.

Understand the failure class

Background: Conflicting config options: "cannot be used together" — configuration validation errors across open-source libraries — this error's family across 162 libraries.

Related errors

AI-assisted analysis of provectus/kafka-ui@83b5a60cc0 (2026-09-08). Data as JSON: /api/errors/c6fb7f065d866ee6. Report an issue: GitHub.

Appendix: source

Thrown at kafka-ui-api/src/main/java/com/provectus/kafka/ui/serdes/SerdesInitializer.java:104

  public ClusterSerdes init(Environment env,
                            ClustersProperties clustersProperties,
                            int clusterIndex) {
    ClustersProperties.Cluster clusterProperties = clustersProperties.getClusters().get(clusterIndex);
    log.debug("Configuring serdes for cluster {}", clusterProperties.getName());

    var globalPropertiesResolver = new PropertyResolverImpl(env);
    var clusterPropertiesResolver = new PropertyResolverImpl(env, "kafka.clusters." + clusterIndex);

    Map<String, SerdeInstance> registeredSerdes = new LinkedHashMap<>();
    // initializing serdes from config
    if (clusterProperties.getSerde() != null) {
      for (int i = 0; i < clusterProperties.getSerde().size(); i++) {
        SerdeConfig serdeConfig = clusterProperties.getSerde().get(i);
        if (Strings.isNullOrEmpty(serdeConfig.getName())) {
          throw new ValidationException("'name' property not set for serde: " + serdeConfig);
        }
        if (registeredSerdes.containsKey(serdeConfig.getName())) {
          throw new ValidationException("Multiple serdes with same name: " + serdeConfig.getName());
        }
        var instance = createSerdeFromConfig(
            serdeConfig,
            new PropertyResolverImpl(env, "kafka.clusters." + clusterIndex + ".serde." + i + ".properties"),
            clusterPropertiesResolver,
            globalPropertiesResolver
        );
        registeredSerdes.put(serdeConfig.getName(), instance);
      }
    }

    // initializing remaining built-in serdes with empty selection patters
    builtInSerdeClasses.forEach((name, clazz) -> {
      if (!registeredSerdes.containsKey(name)) {
        BuiltInSerde serde = createSerdeInstance(clazz);
        if (autoConfigureSerde(serde, clusterPropertiesResolver, globalPropertiesResolver)) {
          registeredSerdes.put(name, new SerdeInstance(name, serde, null, null, null));
        }

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