@XmlRootElement
@XmlAccessorType(XmlAccessType.FIELD)
public class Test {

    @XmlElement(name="id")
    protected Long Id;

    @XmlElement(name = "students")
    protected Set<String> students;

    //Getters and setters
}

@POST
    @Path("/test")
    public String getCounts(JAXBElement<Test> jaxFilters) {
        Test filter = jaxFilter.getValue();
        //Some logic
    }

@POST
@Path("/test")
public String getCounts(JAXBElement<List<Test>> jaxFilters) {
    List<Test> filter = jaxFilter.getValue();
    //Some logic
}