class TransactionResource {

    @GET
    @Path("/transaction/{key}/participants")
    public Response getParticipants(@ApiParam("Encoded hash") @PathParam("key") final String ptmHash) {

        LOGGER.debug("Received participants list API request for key {}", ptmHash);

        MessageHash transactionHash = Optional.of(ptmHash)
            .map(Base64.getDecoder()::decode)
            .map(MessageHash::new).get();

        final String participantList =
                transactionManager.getParticipants(transactionHash).stream()
                        .map(PublicKey::encodeToBase64)
                        .collect(Collectors.joining(","));

        return Response.ok(participantList).build();
    }

    public  TransactionResource(TransactionManager transactionManager);

}