Overriding Existing Marshallers

The Nuxeo Platform provides a flexible JSON marshalling. But sometimes, you'd like to add information from your Information System to the existing JSON or even override it to match your end-user needs.

There may be different needs:

• Add information related to the marshalled object: Try to use built-in parameters, or else create an enricher.

• Add existing informations to the JSON: Try to use built-in parameters, or else extend the existing marshaller.

• Change the existing JSON: Override the existing marshaller.

Enriching an Existing Marshaller

The enrichment mechanism is only enabled for the existing marshallers which extend ExtensibleEntityJsonWriter . That means, almost all of them support enrichment.

An enrichable JSON object provides a contextParameters field which contains all contributions. An enricher is activated if its name is specified in the parameters (for example: enrichers.document=breadcrumb,children). The enricher must write 0, 1 or many key-value in the current JsonGenerator and must let the JsonGenerator in the same state it got it.

{
    ... // the existing generated object
    contextParameters: {  // only present if at least one enricher is activated
        "theFirstEnricherKey": "theFirstEnricherValue",
        "theSecondEnricherKey": { ... },
        "theThirdEnricherKey-Entry1": { ... },
        "theThirdEnricherKey-Entry2": { ... }
    }
}

Let's take the breadcrumb enricher as an example. It contributes to the generated JSON for a document and adds all of the parent documents.

@Setup(mode = Instantiations.SINGLETON, priority = Priorities.REFERENCE)
public class BreadcrumbJsonEnricher extends AbstractJsonEnricher<DocumentModel> { // <= enrich DocumentModel Java type
    public BreadcrumbJsonEnricher() {
        super("breadcrumb"); // <= is activated if "children" is in "enrichers.document" parameter's values
    }
    public void write(JsonGenerator jg, DocumentModel document) throws IOException {
        List<DocumentModel> parentDocuments = null;
        try (SessionWrapper wrapper = ctx.getSession(document)) {
            parentDocuments = wrapper.getSession().getParentDocuments(document.getRef());
        }
        jg.writeFieldName("breadcrumb"); // <= write "breadcrumb" as key
        writeEntity(documentList, jg); // delegates the parent documents marshalling to Nuxeo
    }
}

Of course, like any JSON marshaller, you have to register it.

<?xml version="1.0"?>
<component name="org.nuxeo.example.marshallers">
    <extension target="org.nuxeo.ecm.core.io.MarshallerRegistry" point="marshallers">
        <register class="org.nuxeo.example.BreadcrumbJsonEnricher" enable="true" />
    </extension>
</component>

That's all, you can now use it!

$ curl -X GET 'http://localhost:8080/nuxeo/site/api/v1/path/to/my/document?enrichers.document=breadcrumb'

All existing endpoints which return a DocumentModel will handle the registered enricher.

Extending an Existing JSON Marshaller

If you want to add information at the root level of the existing JSON (not in a contextParameters sub object), you can extend an existing marshaller.

The extending mechanism is only enabled for the existing marshallers which extend ExtensibleEntityJsonWriter . That means, almost all of them support it.

Let's take an example with the DocumentModel. The current marshaller class for DocumentModel is DocumentModelJsonWriter.

@Setup(mode = Instantiations.SINGLETON, priority = Priorities.OVERRIDE_REFERENCE) // <= an higher priority is used
public class MyCustomDocumentModelJsonWriter extends DocumentModelJsonWriter { // <= override the class
    protected void extend(DocumentModel document, JsonGenerator jg) throws IOException { // <= just implement the inherited extend method
        super.extend(document, jg); // optionnal
        jg.writeStringField("additional", "information"); // feel free to write anything
    }
}

Don't forget to register the marshaller. The resulting object will contain the whole existing JSON with your additional data.

All existing endpoints which return a DocumentModel will return the extended JSON.

Overriding an Existing JSON Marshaller

In this case, you want to completely rewrite an existing JSON.

@Setup(mode = Instantiations.SINGLETON, priority = Priorities.OVERRIDE_REFERENCE) // <= an higher priority is used
public class MyCustomDocumentModelJsonWriter extends AbstractJsonWriter<DocumentModel> {
    public void write(DocumentModel document, JsonGenerator jg) throws IOException {
        // generate what you want
    }
}