{"record":{"id":"28a4c5989ac58008","repo":"apache/beam","slug":"unable-to-generate-a-getter-for-field","errorCode":null,"errorMessage":"Unable to generate a getter for field '{}'.","messagePattern":"Unable to generate a getter for field '(.+?)'\\.","errorType":"exception","errorClass":"RuntimeException","httpStatus":null,"severity":"error","filePath":"sdks/java/core/src/main/java/org/apache/beam/sdk/schemas/utils/POJOUtils.java","lineNumber":320,"sourceCode":"            BYTE_BUDDY,\n            field.getDeclaringClass(),\n            typeConversionsFactory.createTypeConversion(false).convert(typeInformation.getType()));\n    builder = implementGetterMethods(builder, typeInformation, typeConversionsFactory);\n    try {\n      return builder\n          .visit(new AsmVisitorWrapper.ForDeclaredMethods().writerFlags(ClassWriter.COMPUTE_FRAMES))\n          .make()\n          .load(\n              ReflectHelpers.findClassLoader(field.getDeclaringClass().getClassLoader()),\n              getClassLoadingStrategy(field.getDeclaringClass()))\n          .getLoaded()\n          .getDeclaredConstructor()\n          .newInstance();\n    } catch (InstantiationException\n        | IllegalAccessException\n        | NoSuchMethodException\n        | InvocationTargetException e) {\n      throw new RuntimeException(\"Unable to generate a getter for field '\" + field + \"'.\", e);\n    }\n  }\n\n  private static <ObjectT, ValueT>\n      DynamicType.Builder<FieldValueGetter<@NonNull ObjectT, ValueT>> implementGetterMethods(\n          DynamicType.Builder<FieldValueGetter<@NonNull ObjectT, ValueT>> builder,\n          FieldValueTypeInformation typeInformation,\n          TypeConversionsFactory typeConversionsFactory) {\n    return builder\n        .visit(new AsmVisitorWrapper.ForDeclaredMethods().writerFlags(ClassWriter.COMPUTE_FRAMES))\n        .method(ElementMatchers.named(\"name\"))\n        .intercept(FixedValue.reference(typeInformation.getName()))\n        .method(ElementMatchers.named(\"get\"))\n        .intercept(new ReadFieldInstruction(typeInformation, typeConversionsFactory));\n  }\n\n  // Implements a method to read a public field out of an object.\n  static class ReadFieldInstruction implements Implementation {","sourceCodeStart":302,"sourceCodeEnd":338,"githubUrl":"https://github.com/apache/beam/blob/12126d8942aaf848030c478b4c6a28c6af861c66/sdks/java/core/src/main/java/org/apache/beam/sdk/schemas/utils/POJOUtils.java#L302-L338","documentation":"createGetter generates a bytecode-implemented FieldValueGetter for a schema field and then warms it up by constructing an instance of the POJO via its no-arg constructor. If code generation or that warm-up instantiation throws, this RuntimeException is raised with the field in the message (cause chain preserved via `e`).","triggerScenarios":"Calling createGetter for a field whose type has no supported getter mapping, or when the transient instantiation of the POJO inside the try block fails (no zero-arg constructor, constructor throws), or ByteBuddy generation fails on the class.","commonSituations":"Fields of exotic types (e.g. generic collections without proper type info) that fail getter generation, POJOs without no-arg constructors tripping the warm-up instantiation, or final classes/methods interfering with bytecode generation.","solutions":["Read the chained cause `e` to determine whether it is a generation error or an instantiation error; fix accordingly.","Add a public zero-argument constructor so the getter warm-up instantiation succeeds.","Simplify or correctly parameterize the field type (e.g. List<String> rather than raw List) so a getter can be generated.","Check field visibility/accessors: ensure a standard bean-style getter exists or the field is accessible."],"exampleFix":"// before\npublic class Item { private List values; } // raw generic type, no no-arg ctor\n// after\npublic class Item {\n  public Item() { }\n  private List<String> values;\n  public List<String> getValues() { return values; }\n}","handlingStrategy":"validation","validationCode":"Field f = MyPojo.class.getDeclaredField(\"values\");\nif (f.getGenericType() instanceof Class) {\n  throw new IllegalStateException(\"Field '\" + f + \"' uses a raw type; Beam cannot generate a getter\");\n}","typeGuard":null,"tryCatchPattern":"try {\n  FieldValueGetter<T, Object> getter = POJOUtils.createGetter(type, typeConversionsFactory);\n} catch (RuntimeException e) {\n  if (e.getMessage() != null && e.getMessage().startsWith(\"Unable to generate a getter\")) {\n    // inspect e.getCause(): fix field type parameterization or add a no-arg ctor\n  } else throw e;\n}","preventionTips":["Always use parameterized collection types in POJO fields.","Keep a public no-arg constructor so getter warm-up instantiation works.","Prefer explicit getters/setters over exotic field access patterns."],"tags":["java","beam-schema","reflection","bytecode"],"backgroundTag":"internal-invariant-violation","analyzedSha":"12126d8942aaf848030c478b4c6a28c6af861c66","analyzedAt":"2026-09-13T01:50:10.254Z","contentChangedAt":"2026-09-13T01:50:10.254Z","schemaVersion":2},"datasetVersion":"2026-09-20T03:17:13.778Z"}