objectify-json-serialization

Serialize custom entity fields to/from JSON with Objectify

Before

Look at custom and someMap properties. By default Objectify doesn't know how to serialize them, so it uses Datastore's EmbeddedEntity.

After

With @SerializeToJson annotation and SerializeToJsonTranslatorFactory - Objectify uses JSON serialization. Nice!

Problem

Well described in issue by @stickfigure:

I am missing an annotation, which allows me to serialize and store an object graph using Json instead of Java Serialization.

Json is much more flexible, tolerant and faster, and I would love to see it in objectify natively.

Details:

1. Java Serialization is opaque, Json is human readable.
2. Java Serialization typically takes longer and produces a larger file than Json.
3. And most important: The main problem with Java Serialization is versioning. By default, it stores the full package name of a class. Even simple refactoring will break it and render the stored data unreadable. Java Serialization may be an acceptable technique for wrapping data short-term (such as for example data that is transferred over REST and immediately unwrapped on the other side), but I don't consider it suitable for long-term data storage (such as data store), as schemas evolve over time.

Solution

Add @SerializeToJson annotation to the fields you want to be serialized as JSON:

@Entity
public class MyEntity {

    @Id
    private Long id;

    private String userName;

    private Integer age;

    @SerializeToJson
    private Map<String,Integer> someMap;

    @SerializeToJson
    private CustomModel custom;
}

Implementation

Most of the magic is done in SerializeToJsonTranslatorFactory.

Register it like this:

ObjectifyService.factory().getTranslators().addEarly(new SerializeToJsonTranslatorFactory(new JacksonStringifierFactory()));

Note that addEarly() is used instead of normal add(). Otherwise other TranslatorFactory that's built-in in Objectify takes priority.

I abstracted away JSON implementation behind Stringifier, StringifierFactory and provided implementation for Jackson in
JacksonStringifier, JacksonStringifierFactory.

License

MIT © Kirill Groshkov