apache/beam · error · RuntimeException

Was not able to generate getters for schema: {} class: {}

Error message

Was not able to generate getters for schema: {} class: {}

What it means

POJOUtils.getGetters generates runtime getter classes for a POJO matching its inferred schema. After generating one getter per resolved type it validates the count against schema.getFieldCount(); if the number of generated getters does not match the schema's field count, it throws this RuntimeException, meaning schema inference and reflection disagreed.

Source

Thrown at sdks/java/core/src/main/java/org/apache/beam/sdk/schemas/utils/POJOUtils.java:120

  public static <T> List<FieldValueGetter<@NonNull T, Object>> getGetters(
      TypeDescriptor<T> typeDescriptor,
      Schema schema,
      FieldValueTypeSupplier fieldValueTypeSupplier,
      TypeConversionsFactory typeConversionsFactory) {
    // Return the getters ordered by their position in the schema.
    return (List)
        CACHED_GETTERS.computeIfAbsent(
            TypeDescriptorWithSchema.create(typeDescriptor, schema),
            c -> {
              List<FieldValueTypeInformation> types =
                  fieldValueTypeSupplier.get(typeDescriptor, schema);
              List<FieldValueGetter<@NonNull T, Object>> getters =
                  types.stream()
                      .<FieldValueGetter<@NonNull T, Object>>map(
                          t -> POJOUtils.createGetter(t, typeConversionsFactory))
                      .collect(Collectors.toList());
              if (getters.size() != schema.getFieldCount()) {
                throw new RuntimeException(
                    "Was not able to generate getters for schema: "
                        + schema
                        + " class: "
                        + typeDescriptor);
              }
              return (List) getters;
            });
  }

  // The list of constructors for a class is cached, so we only create the classes the first time
  // getConstructor is called.
  public static final Map<TypeDescriptorWithSchema<?>, SchemaUserTypeCreator> CACHED_CREATORS =
      Maps.newConcurrentMap();

  public static <T> SchemaUserTypeCreator getSetFieldCreator(
      TypeDescriptor<T> typeDescriptor,
      Schema schema,
      FieldValueTypeSupplier fieldValueTypeSupplier,

View on GitHub (pinned to 12126d8942)

Solutions

Regenerate the schema from the current POJO (POJOUtils.schemaFromType / Schema inference) so field count matches the class.
Ensure the same class version and classpath are used at pipeline construction and at runtime (fat jar / staging consistency).
Check whether multiple mapped types (types.stream()) legitimately yield more getters than schema fields; align @SchemaFieldNumber/name annotations with the schema.
Use SchemaCoder/serialization consistency: clear any stale cached schema and rebuild the coder.

Example fix

// before
Schema schema = Schema.builder().addInt32Field("a").build(); // stale: POJO now has 'a' and 'b'
List<FieldValueGetter<T, Object>> getters = POJOUtils.getGetters(TypeDescriptor.of(MyPojo.class), schema, factory);
// after
Schema schema = POJOUtils.schemaFromType(TypeDescriptor.of(MyPojo.class)); // inferred from current class

Defensive patterns

Strategy: validation

Validate before calling

Schema inferred = POJOUtils.schemaFromType(TypeDescriptor.of(MyPojo.class));
if (!inferred.equivalent(schema)) {
  throw new IllegalStateException("Registered schema stale: expected " + inferred + " got " + schema);
}

Try / catch

try {
  List<FieldValueGetter<T, Object>> getters = POJOUtils.getGetters(td, schema, factory);
} catch (RuntimeException e) {
  if (e.getMessage() != null && e.getMessage().startsWith("Was not able to generate getters")) {
    schema = POJOUtils.schemaFromType(td); // re-infer and retry once
  } else throw e;
}

Prevention

Always infer the schema from the live class instead of caching it across deploys.
Keep the POJO classpath identical between job submission and workers.
Use @SchemaFieldNumber/@SchemaFieldDefault annotations so field order/count is stable.

When it happens

Trigger: Calling getGetters(typeDescriptor, schema, typeConversionsFactory) when the schema was produced for a different class version (fields added/removed between inference and use), when field name-case normalization collapses distinct fields, or when the passed schema does not correspond to typeDescriptor.

Common situations: Schema registered/cached from an older POJO version (serialization by Schemas at pipeline submit vs runtime classpath mismatch), heterogeneous subclasses in a union being flattened, or manually built schemas missing/extra fields.

Understand the failure class

Background: Schema validation failed / invalid input schema: payload rejected because its shape doesn't match the expected schema — this error's family across 28 libraries.

Related errors

AI-assisted analysis of apache/beam@12126d8942 (2026-09-13). Data as JSON: /api/errors/60b670b6f96efebd. Report an issue: GitHub.