Hyrrokkin

Hyrrokkin is a Java library to convert POJOs into a JSON feed that Ember Data can consume via its RESTAdapter. The name Hyrrokkin comes from Norse and means "Fire-smoked". Hyrokkin is also a dark, shrivelled giantess that helped get Balders ship Hringhorni rolled out to sea. (http://en.wikipedia.org/wiki/Hyrrokkin)

In its first version, Hyrrokkin will support translating any POJO (Plain Old Java Object) into a JSON that the RESTAdapter understands. This means that it will flatten the object-tree and side-load any embedded data types into the JSON.

Currently Hyrrokkin uses the GSON library in the background. This dependency might be removed in the future, making Hyrrokkin completely self-contained.

Building up the Data

Usually, models on the server might have fields that you do not want to send over the wire from the server to the client. Hyrrokkin expects you to annotate any fields/properties that you want to expose to the client with the @Expose annotation. In addition, it is possible to change the name of a property using the @SerializedName, while it is possible to override the rootKey of a class via the @SerializedClassName

Consider the following two class definitions:

@SerializedClassName("session")
public class Session {
    @Expose
    @SerializedName("id")
    private String uuid;

    @Expose
    private User user;

    @Expose
    private boolean authenticated;

    @Expose
    private Long lastAccessed;

    @Expose
    private List<User> users;

    private boolean isLoaded;
}

@SerializedClassName("user")
public class MySystemUserUser extends User {
    @Expose private Integer id;
    @Expose private String email;
    @Expose private Integer groupId;
    @Expose private Date createdAt;
    @Expose private User user;
}

As you can see from the class above, we have marked the properties that we want to expose to the client side with the @Expose annotation. This means that the property "isLoaded" wont be included when the object is serialized into JSON. Additionally, we have also maked the uuid-property of the Session class with the @SerializedName annotation. This means that the uuid property will become serialized into the "id"-property in the resulting JSON.

Notice also, that we have overridden the root keys of both classes using the @SerializedClassName annotation

The resulting JSON, after serialization thus becomes:

{
    "session": {
        "id": "abcabvabv",
        "user": "1",
        "authenticated": true,
        "lastAccessed": 1418254183981,
        "users": [
            45,
            2
        ]
    }
	"users": [
        {
            "id": 2,
            "email": "user email2",
            "groupId": 6,
            "createdAt": "2014-12-10T23:29:43Z"
        },
        {
            "id": 1,
            "email": "user email",
            "groupId": 4,
            "user": "2"
        },
        {
            "id": 45,
            "email": "user email4",
            "groupId": 3
        }
    ]
}

Is it production ready?

At this point, not really. It's definately usable, but the code needs to be cleaned up a bit and a few extra features needs to be added. I am personally using this serializer in my projects, but your mileage might vary depending on your requirements.

Currently, there are some empty try-catch blocks that also needs to be refactored properly, as they currently swallow some exceptions without handling them in a proper manner :)

Especially in order to support other serializing targets (like JSON API), a cleanup is needed. The code for Hyrrokkin is extracted from a larger project, and thus will be updated moving forward.

How to use it

Using the serializer is quite straight forward. Simply instantiate a RestSerializer class and execite the serialize method.

Session session = repository.getSession(uuid);

RestSerializer rs = new RestSerializer();
JsonElement jsonElement = rs.serialize(session);

if(jsonElement != null) {
    responseContent = jsonElement.toString();
}

What about JSON API?

There is a JSON API seraializer planned

Tests

While there are no tests committed just yet, the project does have tests. As Hyrrokkin is extracted from a larger project, test will be committed as soon as these can be extracted without also bringing the domain of that application with it :)