JSON-LD blank node to nested object in Apache Jena

Question

I have the following example Turtle document:

@prefix dct:    .
@prefix rdf:   <         


        

Answer 1

You can use jsonld-java with framing to convert your JSON-LD result to nice nested JSON. The result of the conversion will be semantically equivalent.

Try

    private static String getPrettyJsonLdString(String rdfGraphAsJson) {
        try {
        //@formatter:off
                return JsonUtils
                        .toPrettyString(
                                getFramedJson(
                                        createJsonObject(
                                                        rdfGraphAsJson)));
        //@formatter:on
        } catch (Exception e) {
            throw new RuntimeException(e);
        }
    }


    private static Map<String, Object> getFramedJson(Object json) {
        try {
            return JsonLdProcessor.frame(json, getFrame(), new JsonLdOptions());
        } catch (Exception e) {
            throw new RuntimeException(e);
        }
    }

    private static Map<String, Object> getFrame() {
        Map<String, Object> frame = new HashMap<>();
        /*
          Use @type to define 'root' object to embed into
        */
        frame.put("@type" , "dcat:Distribution");
        Map<String,Object>context=new HashMap<>();
        context.put("dct", "http://purl.org/dc/terms/");
        context.put("rdf", "http://www.w3.org/1999/02/22-rdf-syntax-ns#");
        context.put("dcat", "http://www.w3.org/ns/dcat#");
        context.put("example", "http://example.com/vocabulary/");
        frame.put("@context", context);
        return frame;
    }

    private static Object createJsonObject(String ld) {
        try (InputStream inputStream =
                new ByteArrayInputStream(ld.getBytes(Charsets.UTF_8))) {
            Object jsonObject = JsonUtils.fromInputStream(inputStream);
            return jsonObject;
        } catch (Exception e) {
            throw new RuntimeException(e);
        }
    }

This will produce

{
  "@context" : {
    "dct" : "http://purl.org/dc/terms/",
    "rdf" : "http://www.w3.org/1999/02/22-rdf-syntax-ns#",
    "dcat" : "http://www.w3.org/ns/dcat#",
    "example" : "http://example.com/vocabulary/"
  },
  "@graph" : [ {
    "@id" : "http://example.com/datasets/1",
    "@type" : "dcat:Distribution",
    "example:props" : {
      "@id" : "_:b0",
      "example:prop1" : "hello",
      "example:prop2" : "1"
    }
  } ]
}

Answer 2

You need to re-frame the graph as the top-level object. You can use either:

{
  "@context": ...,
  "@type": "dcat:Distribution"
}

or

{
  "@context": ...,
  "@id": "http://example.com/datasets/1"
}

or

{
  "@context": ...,
  "example:props": {}
}

(i.e. object that contains any "example:props").

Answer 3

Apache Jena uses jsonld-java for JSON-LD input and output.

It is possible to setup the jsonld-java output as shown with:

https://jena.apache.org/documentation/io/rdf-output.html#json-ld ==> https://github.com/apache/jena/blob/master/jena-arq/src-examples/arq/examples/riot/Ex_WriteJsonLD.java

You'll need to consult jsonld-java as to whether the writer can do what you want.