apache/beam · error · RuntimeException

Getter has wrong prefix <method>

Error message

Getter has wrong prefix <method>

What it means

Thrown by FieldValueTypeInformation.forGetter when a method is being introspected as a getter but its name does not start with the recognized prefixes "get" or "is". The schema framework only accepts JavaBean-style getters, so any other method passed as a getter fails.

Source

Thrown at sdks/java/core/src/main/java/org/apache/beam/sdk/schemas/FieldValueTypeInformation.java:206

    if (fieldDescription == null) {
      return null;
    }
    return fieldDescription.value();
  }

  public static FieldValueTypeInformation forGetter(Method method, int index) {
    return forGetter(null, method, index);
  }

  public static FieldValueTypeInformation forGetter(
      @Nullable TypeDescriptor<?> typeDescriptor, Method method, int index) {
    String name;
    if (method.getName().startsWith("get")) {
      name = ReflectUtils.stripPrefix(method.getName(), "get");
    } else if (method.getName().startsWith("is")) {
      name = ReflectUtils.stripPrefix(method.getName(), "is");
    } else {
      throw new RuntimeException("Getter has wrong prefix " + method.getName());
    }

    TypeDescriptor<?> type =
        Optional.ofNullable(typeDescriptor)
            .map(td -> (TypeDescriptor) td.resolveType(method.getGenericReturnType()))
            // fall back to previous behavior
            .orElseGet(() -> TypeDescriptor.of(method.getGenericReturnType()));

    boolean nullable = hasNullableReturnType(method);
    return new AutoValue_FieldValueTypeInformation.Builder()
        .setName(getNameOverride(name, method))
        .setNumber(getNumberOverride(index, method))
        .setNullable(nullable)
        .setType(type)
        .setRawType(type.getRawType())
        .setMethod(method)
        .setElementType(getIterableComponentType(type))
        .setMapKeyType(getMapKeyType(type))

View on GitHub (pinned to 12126d8942)

Solutions

1. Rename the method to start with get (or is for boolean return types).
2. If the method is not a field getter, exclude it from schema introspection (e.g. make it private or annotate the class schema accordingly).
3. Use @SchemaFieldName on a properly-prefixed getter to control the schema field name instead of custom prefixes.

Example fix

// before
public String fetchName() { ... }

// after
public String getName() { ... }

for (Method m : clazz.getMethods()) { if (m.getParameterCount() == 0 && !m.getName().startsWith("get") && !m.getName().startsWith("is") && !java.lang.reflect.Modifier.isStatic(m.getModifiers())) { /* exclude or rename before registering */ } }

static boolean isBeanGetter(Method m) { return m.getParameterCount() == 0 && (m.getName().startsWith("get") || m.getName().startsWith("is")) && !m.getReturnType().equals(void.class); }

try { schemaOf(clazz); } catch (RuntimeException e) { if (e.getMessage().startsWith("Getter has wrong prefix")) { /* rename method or exclude from schema */ } else { throw e; } }

When it happens

Trigger: Passing a method whose name lacks the get/is prefix to forGetter; schema discovery routing a non-getter method (e.g. calculateTotal or fetchName) into getter handling.

Common situations: Custom getter prefixes (e.g. `fetch`, `retrieve`) in bean-like classes; fluent-style getters returning this without prefix; methods inherited from interfaces that don't follow JavaBean conventions.

Understand the failure class

Background: "Invalid ... format", "must be in format X", "does not look like a ..." — invalid argument format errors across CLI tools and libraries — this error's family across 17 libraries.

Related errors

• Setter has wrong prefix <method>
• Setter methods should take a single argument <method>
• @SchemaFieldNumber can only be used on getters in Java Beans
• @SchemaFieldName can only be used on getters in Java Beans.
• Could not determine array parameter type for field.

AI-assisted analysis of apache/beam@12126d8942 (2026-09-13). Data as JSON: /api/errors/09344fd2a798eccb. Report an issue: GitHub.