How to use

DoFnSignature$FieldAccessDeclaration

in

org.apache.beam.sdk.transforms.reflect

private static Map<String, DoFnSignature.FieldAccessDeclaration> analyzeFieldAccessDeclaration(
  ErrorReporter errors, Class<?> fnClazz) {
 Map<String, FieldAccessDeclaration> fieldAccessDeclarations = new HashMap<>();
 for (Field field : declaredFieldsWithAnnotation(DoFn.FieldAccess.class, fnClazz, DoFn.class)) {
  field.setAccessible(true);
  DoFn.FieldAccess fieldAccessAnnotation = field.getAnnotation(DoFn.FieldAccess.class);
  if (!Modifier.isFinal(field.getModifiers())) {
   errors.throwIllegalArgument(
     "Non-final field %s annotated with %s. Field access declarations must be final.",
     field.toString(), DoFn.FieldAccess.class.getSimpleName());
   continue;
  }
  Class<?> fieldAccessRawType = field.getType();
  if (!fieldAccessRawType.equals(FieldAccessDescriptor.class)) {
   errors.throwIllegalArgument(
     "Field %s annotated with %s, but the value was not of type %s",
     field.toString(),
     DoFn.FieldAccess.class.getSimpleName(),
     FieldAccessDescriptor.class.getSimpleName());
  }
  fieldAccessDeclarations.put(
    fieldAccessAnnotation.value(),
    FieldAccessDeclaration.create(fieldAccessAnnotation.value(), field));
 }
 return fieldAccessDeclarations;
}

public void addFieldAccessDeclaration(FieldAccessDeclaration decl) {
 fieldAccessDeclarations.put(decl.id(), decl);
}

checkArgument(
  fieldAccessDeclaration != null, "No FieldAccessDeclaration defined with id", id);
checkArgument(fieldAccessDeclaration.field().getType().equals(FieldAccessDescriptor.class));
try {
 fieldAccessDescriptor = (FieldAccessDescriptor) fieldAccessDeclaration.field().get(fn);
} catch (IllegalAccessException e) {
 throw new RuntimeException(e);

checkArgument(
  fieldAccessDeclaration != null, "No FieldAccessDeclaration  defined with id", id);
checkArgument(fieldAccessDeclaration.field().getType().equals(FieldAccessDescriptor.class));
try {
 fieldAccessDescriptor = (FieldAccessDescriptor) fieldAccessDeclaration.field().get(fn);
} catch (IllegalAccessException e) {
 throw new RuntimeException(e);

@Test
public void testFieldAccess() throws IllegalAccessException {
 FieldAccessDescriptor descriptor = FieldAccessDescriptor.withFieldNames("foo", "bar");
 DoFn<String, String> doFn =
   new DoFn<String, String>() {
    @FieldAccess("foo")
    final FieldAccessDescriptor fieldAccess = descriptor;
    @ProcessElement
    public void process(@FieldAccess("foo") Row row) {}
   };
 DoFnSignature sig = DoFnSignatures.getSignature(doFn.getClass());
 assertThat(sig.fieldAccessDeclarations().get("foo"), notNullValue());
 Field field = sig.fieldAccessDeclarations().get("foo").field();
 assertThat(field.getName(), equalTo("fieldAccess"));
 assertThat(field.get(doFn), equalTo(descriptor));
 assertThat(sig.processElement().getRowParameter(), notNullValue());
}