@EJB
private ProxyBeanLocal proxyBean;

@WebMethod(operationName = "hello")
public String hello(@WebParam(name = "name") String txt) {
    return proxyBean.businessMethod();
}

@Stateless
public class ProxyBean implements ProxyBeanLocal {

private final String ADAPTER_1_URL = "";
private final String ADAPTER_2_URL = "";
ConcurrentMap<String, String> m;

@Override
public String businessMethod() {

    try {
        m = new ConcurrentHashMap<>();

        AdapterWS_Service serviceAdapter = new AdapterWS_Service(new URL(ADAPTER_1_URL));
        AdapterWS adapter = serviceAdapter.getAdapterWSPort();

        adapter.helloAsync("", this);//call async with callback on this

        serviceAdapter = new AdapterWS_Service(new URL(ADAPTER_2_URL));
        adapter = serviceAdapter.getAdapterWSPort();

        adapter.helloAsync("", this);


    } catch (MalformedURLException ex) {
        Logger.getLogger(ProxyBean.class.getName()).log(Level.SEVERE, null, ex);
    }

    return null; //return recordset once all responses arrived (using blocking queue?)

}

@Override
public void handleResponse(Response<HelloResponse> res) {
    try {
        m.put(res.get().getReturn(), res.get().getReturn());
    } catch (InterruptedException ex) {
        Logger.getLogger(ProxyBean.class.getName()).log(Level.SEVERE, null, ex);
    } catch (ExecutionException ex) {
        Logger.getLogger(ProxyBean.class.getName()).log(Level.SEVERE, null, ex);
    }
}