JAX-RS filter to validate query parameter

JAXRSReqFilter.java

@Provider
@QueryParamValidator
public class JAXRSReqFilter implements ContainerRequestFilter{

    @Override
    public void filter(ContainerRequestContext requestContext) throws IOException {
        
        MultivaluedMap<String, String> queryParameters = requestContext.getUriInfo().getQueryParameters();
        
        String queryParam = queryParameters.keySet().stream().findFirst().get();
        System.out.println("Query param - "+ queryParam);
        
        if(!queryParam.equals("p")){
            requestContext.abortWith(Response
                    .status(Response.Status.BAD_REQUEST)
                    .entity("Invalid Query Param "+ queryParam)
                    .build());
        }
    }
    
}