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# 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:
```java
@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`].
```java
@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:
```java
@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].
[`AutoValue`]: https://github.com/google/auto/tree/master/value
[`SerializableAutoValue`]: https://github.com/google/auto/blob/master/value/src/main/java/com/google/auto/value/extension/serializable/SerializableAutoValue.java
[`SerializableAutoValueExtension`]: https://github.com/google/auto/blob/master/value/src/main/java/com/google/auto/value/extension/serializable/extension/SerializableAutoValueExtension.java
[SerializerExtensions]: https://github.com/google/auto/blob/master/value/src/main/java/com/google/auto/value/extension/serializable/userguide/serializer-extension.md
|
