从JSON-Ld访问Java中的数据

Question

my server is receiving different JSON-LD messages as a string. I now need to acces these messages. Here is an example:

    {
  "@graph": [
    {
      "@graph": [
        {
          "@id": "InterIoTMsg:meta/b453273f-36d6-49a2-82ec-d909d8e6f10a",
          "@type": [
            "InterIoTMsg:meta",
            "InterIoTMsg:Observation"
          ],
          "InterIoTMsg:ReceiverPlatformId": {
            "@id": "http://om2m.org/myPlatform"
          },
          "InterIoTMsg:conversationID": "conv614d3621-7399-45b1-bf2f-505b24045ea6",
          "InterIoTMsg:dateTimeStamp": "2018-01-15T21:49:00.655+01:00",
          "InterIoTMsg:messageID": "msg7713aa0f-61df-471d-beec-80e8fb71528a"
        }
      ],
      "@id": "InterIoTMsg:metadata"
    },
    {
      "@graph": [
        {
          "@id": "_:b1",
          "@type": "sosa:Observation",
          "iiot:hasName": "tempOutside",
          "sosa:resultTime": {
            "@type": "http://www.w3.org/2001/XMLSchema#dateTime",
            "@value": "2018-04-06T12:36:12Z"
          },
          "sosa:hasResult": {
            "@id": "_:b2"
          },
          "sosa:madeBySensor": {
            "@id": "_:b0"
          }
        },
        {
          "@id": "_:b2",
          "@type": "sosa:Result",
          "iiot:hasResultValue": {
            "@type": "http://www.w3.org/2001/XMLSchema#long",
            "@value": "32"
          },
          "iiot:hasUnit": {
            "@id": "sweet_units:celsius"
          }
        },
        {
          "@id": "http://localhost:8080/weather/station1",
          "@type": "http://inter-iot.eu/GOIoTP#IoTDevice",
          "InterIoT:GOIoTP#hasName": "Weather Station 1"
        },
        {
          "@id": "_:b0",
          "@type": "sosa:Sensor",
          "sosa:isHostedBy": {
            "@id": "http://localhost:8080/in-name/humidity"
          }
        }
      ],
      "@id": "InterIoTMsg:payload"
    }
  ],
  "@context": {
    "InterIoTMsg": "http://inter-iot.eu/message/",
    "InterIoT": "http://inter-iot.eu/",
    "sosa": "http://www.w3.org/ns/sosa/",
    "iiot": "http://inter-iot.eu/GOIoTP#"
  }
}

I don't know exactly how to access specific values in the data. For example value in iiot:hasResultValue . What I have right now is a RDF-Parser which parses the String to a dataset with the help of the Jena Api:

try (InputStream in = new ByteArrayInputStream(message.getBytes(StandardCharsets.UTF_8))) {
        RDFParser.create()
                .source(in)
                .lang(Lang.JSONLD)
                .parse(dataset.asDatasetGraph());
    }

First of all I don't know how to continue at this point, and second I don't even know if this is the right rudiment. So if anybody could help I am very grateful.

Answer 1

From the description, you probably want the RDF data in a model then use the model API to access the data in the model.

The first thing to try is print as Turtle so you can see the structure of the RDF.

Model model = ModelFactory.createDefaultModel();
RDFDataMgr.read(model, new StringReader(message), null, Lang.JSONLD);
RDFDataMgr.write(System.out, model, Lanmg.TURTLE);

The RDFDataMgr.read can also be done with:

RDFParser.create().fromString(message).lang(Lang.JSONLD).parse(model);