As it closes, recursively closing every "AutoCloseable" field marked with the "Owns" annotation as well.

AutoCloseable2.java

import java.lang.reflect.Field;
import java.util.Collection;
import java.util.stream.Stream;
import java.util.stream.Collectors;

public interface AutoCloseable2 extends AutoCloseable {

  @Override
  public default void close() throws Exception {
    for (Field field : getClass().getDeclaredFields()) {
      if (field.getAnnotation(Owns.class) != null) {
        for (AutoCloseable e : toAutoCloseableObjects(field.get(this)).collect(Collectors.toList())) e.close();
      }
    }
  }

  static Stream<AutoCloseable> toAutoCloseableObjects(Object obj) {
    if (obj instanceof AutoCloseable) {
      return Stream.of((AutoCloseable) obj);
    }
    if (obj instanceof Collection<?>) {
      return ((Collection<?>) obj).stream().flatMap(AutoCloseable2::toAutoCloseableObjects);
    }
    return Stream.of();
  }

}

build.sbt

name := "autoClose"

javacOptions ++= Seq(
  "-source" -> "1.8",
  "-target" -> "1.8"
).flatMap(_.productIterator.map(_ +""))

Main.java

import java.util.*;

public class Main {

  public static void main(String[] args) throws Exception {

    Foo foo = new Foo("parent",
      new Foo("child#1",
        new Bar("grandchild#1/1", Arrays.asList()),
        new Bar("grandchild#1/2", Arrays.asList())
      ),
      new Bar("child#2", Arrays.asList(
        new Bar("grandchild#2/1", Arrays.asList()),
        new Bar("grandchild#2/2", Arrays.asList())
      ))
    );

    foo.close();
  }

  static class Foo implements AutoCloseable2 {

    String key;

    @Owns
    AutoCloseable bar;

    @Owns
    AutoCloseable baz;

    Foo(String key, AutoCloseable bar, AutoCloseable baz) {
      this.key = key;
      this.bar = bar;
      this.baz = baz;
    }

    @Override
    public void close() throws Exception {
      AutoCloseable2.super.close();
      System.err.println("Foo@" + key + " is being closed..");
    }
  }

  static class Bar implements AutoCloseable2 {

    String key;

    @Owns
    List<AutoCloseable> children;

    Bar(String key, List<AutoCloseable> children) {
      this.key = key;
      this.children = children;
    }

    @Override
    public void close() throws Exception {
      AutoCloseable2.super.close();
      System.err.println("Bar@" + key + " is being closed..");
    }
  }

}

Owns.java

import java.lang.annotation.ElementType;
import java.lang.annotation.Target;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;

@Target(ElementType.FIELD)
@Retention(RetentionPolicy.RUNTIME)
public @interface Owns {
}