Simple server returns the json response

json_server.psgi

use JSON;
use Plack::Request;

my $app = sub {
    my $req = Plack::Request->new(shift);

    my $res = $req->new_response(200);
    $res->content_type('application/json');
    $res->body(encode_json(+{
        method => $req->method,
        query_strings => $req->query_parameters->as_hashref,
        body_parameters => $req->body_parameters->as_hashref,
        message => 'Hello JSON World!',
    }));

    return $res->finalize;
};