Introducing Siren 4 Java EE 1.0

#jaxrs #hypermedia thursday, june 02, 2016

When implementing a Hypermedia driven REST API you may need to choose an content type upfront. If you use the Siren content type together with Java EE there are several approaches to create Siren entity responses.

As your links and actions in your reponses may dynamically change depending on your business logic (e.g. some links or actions are only valid in certain situations), it makes sense to use a programmatic rather than declarative approach. Siren4J offers a simple way to both programmatically and declaratively create Siren responses. However this library contains a few third-party dependencies, for instance Jackson.

If you want a leaner approach using plain Java EE 7 you can either use JSON output created by JSONP or a lean library called Siren 4 Java EE. The idea of the latter is to only depend on the Java EE 7 API and therefore use JSONP internally.

Siren 4 Java EE is used as follows:

<dependency>
    <groupId>com.sebastian-daschner</groupId>
    <artifactId>siren4javaee</artifactId>
    <version>1.0</version>
</dependency>

JsonObject bookEntity = Siren.createEntityBuilder()
    .addClass("book")
    .addProperty("isbn", book.getIsbn())
    .addProperty("name", book.getName())
    .addProperty("author", book.getAuthor())
    .addProperty("availability", book.getAvailability().toString())
    .addProperty("price", book.getPrice())
    .addLink(bookUri, "self")
    .addAction(Siren.createActionBuilder()
        .setName("add-to-cart")
        .setTitle("Add book to cart")
        .setMethod(HttpMethod.POST)
        .setHref(shoppingCartUri)
        .setType(MediaType.APPLICATION_JSON)
        .addField("isbn", FieldType.TEXT)
        .addField("quantity", FieldType.NUMBER)).build();

For a more comprehensive example see the siren4javaee approach in Hypermedia with JAX-RS.

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