How to get the value of Owned by attribute using HTTP Client Query method(Custom Java implementation)?

It looks like rtc_cm:ownedBy is not defined as property.

Have you checked the resource shape for resources of that type in that project area to see what properties are defined?

Or looked at the RDF of an example work item from that project area to see how owner is represented?

If I look at work items on jazz.net I do not see a rtc_cm:ownedBy propery. Instead, the owner is represented by dcterms:contributor as per the OSLC Change Management specification - see https://docs.oasis-open-projects.org/oslc-op/cm/v3.0/os/change-mgt-shapes.html#changerequest.

If I look at the resource shape, I see it contains:

<https://jazz.net/jazz/oslc/shapes/workitems/_yOoaIKY7Ee2RrPFw5xrdAg/property/owner>
      a       oslc:Property ;
      oslc:allowedValues <https://jazz.net/jazz/oslc/shapes/workitems/_yOoaIKY7Ee2RrPFw5xrdAg/property/owner/allowedValues> ;
      oslc:defaultValue <https://jazz.net/jts/users/unassigned> ;
      oslc:name "contributor"^^<http://www.w3.org/2001/XMLSchema#string> ;
      oslc:occurs oslc:Zero-or-one ;
      oslc:propertyDefinition
              dcterms:contributor ;
      oslc:range <http://xmlns.com/foaf/0.1/Person> ;
      oslc:readOnly "false"^^<http://www.w3.org/2001/XMLSchema#boolean> ;
      oslc:representation oslc:Either ;
      oslc:valueType oslc:Resource ;
      dcterms:title "Owned By"^^rdf:XMLLiteral .
        

Which tells me that dcterms:contributor is the property for owner.

Note that application/json is not an RDF media type. While some ELM application REST services might support it, the JSON representation is not defined by OSLC. Clients doing so are likely to become dependent on proprietary and undocumented JSON representations. You can represent RDF as json using JSON-LD for which the media type is application/ld+json . However, few, if any, ELM REST services currently support that media type.

One thing I notice is that your code example is manually constructing the requiest URI. This is bad practice. Instead, you should be using OSLC discovery to find the query base URI of the OSLC query capability you want to use. See https://docs.oasis-open-projects.org/oslc-op/core/v3.0/os/discovery.html.In that way, if an OSLC server changes the endpoint URIs in a later release, then clients should not be impacted. If you hard code assumptions about the paths, your OSLC client code will be more fragile and likely to break if such changes happen.

Lastly, 6.0.6.1 went end of service on 2022-10-31 and will no longer be remediated against security vulnerabilities. I highly recommend you upgrade to 7.0.2.