AutoValue: Defensive Copiers

An extension for Google's AutoValue that hides mutable objects behind defensive copiers, creating true immutable objects.

Usage

Annotate any properties in your @AutoValue-annotated class that should be defensively copied when accessed with @DefensiveCopy

@AutoValue public abstract class Customer {

  // immutable, needs no defensive copying
  public abstract String firstName();

  // could be mutated by external sources; should be hidden using @DefensiveCopy
  @DefensiveCopy public abstract List<String> orderIDs();
}

This supports a small set of built-in Java classes (currently, all Collections, as well as java.util.Date). Other classes require a custom implementation by the user. This can be accomplished by using @DefensiveCopy(copier = MyCopier.class), where MyCopier implements DefensiveCopier<T> (where T is the property's return type)

@AutoValue public abstract class Location {
  public abstract String streetAddress();
  public abstract int zipCode();

  @DefensiveCopy(copier = PointCopier.class) public abstract java.awt.Point coordinates();
}

And then implement PointCopier as such:

public class PointCopier extends DefensiveCopier<Point> {
  @NotNull @Override public Point defensiveCopy(@NotNull Point source) {
    return new Point(source); // copy-constructor ensures the caller can never modify the source
  }
}

Download

Add JitPack at the end of your list of repositories if you haven't already:

repositories {
  ... // jcenter(), mavenCentral(), etc
  maven { url "https://jitpack.io" }
}

Now add the dependencies:

dependencies {
  compileOnly "com.github.kevinmost.auto-value-defensive-copy:adapter:[version]"
  apt "com.github.kevinmost.auto-value-defensive-copy:processor:[version]"
}