Serializable AutoValue Extension

An AutoValue extension that enables @AutoValue classes with un-serializable properties to be serializable.

Usage

To use the SerializableAutoValueExtension with your AutoValue class, the AutoValue class must:

1. Implement java.io.Serializable.
2. Be annotated with @SerializableAutoValue.

Example

The following AutoValue class is un-serializable:

@AutoValue
public abstract class Foo implements Serializable {

  public static Foo create(Optional<String> x) {
    return new AutoValue_Foo(x);
  }

  // java.util.Optional is not serializable.
  abstract Optional<String> x;
}

This is because java.util.Optional is un-serializable. We can make Foo serializable by using the SerializableAutoValueExtension.

@SerializableAutoValue  // This annotation activates the extension.
@AutoValue
public abstract class Foo implements Serializable {
  ...
}

Details

For the example class Foo above, SerializableAutoValueExtension will generate the following code:

@Generated("SerializableAutoValueExtension")
final class AutoValue_Foo extends $AutoValue_Foo {

  // Instead of serializing AutoValue_Foo, we delegate serialization to a
  // proxy object.
  Object writeReplace() throws ObjectStreamException {
    return new Proxy$(this.x);
  }

  // When serializing, AutoValue_Foo's values are written to Proxy$.
  // When de-serializing, Proxy$'s values used to create a new instance of
  // AutoValue_Foo
  static class Proxy$ implements Serializable {

    private String x;

    // During serialization, un-wrap the Optional field.
    Proxy$(Optional<String> x) {
      this.x = x.orElse(null);
    }

    // During de-serialization, re-create AutoValue_Foo.
    Object readResolve() throws ObjectStreamException {
      return new AutoValue_Foo(Optional.ofNullable(x));
    }
  }
}

SerializableAutoValueExtension delegates the serialization of Foo to a proxy object Proxy$ where Foo's data is unwrapped.

Supported Types

SerializableAutoValueExtension currently supports the following types:

• java.util.Optional
• com.google.common.collect.ImmutableList
  • Enables ImmutableList<T>, where T is an un-serializable but supported type, to be serializable.
• com.google.common.collect.ImmutableMap
  • Enables ImmutableMap<K, V>, where K and/or V are un-serializable but supported types, to be serializable.

Extensions

SerializableAutoValueExtension can be extended to support additional un-serializable types with SerializerExtensions.