@SuppressWarnings("unchecked")
    public T value() {
        if (!succeeded())
            throw new IllegalStateException("Attempt to retrieve value from future which hasn't successfully completed");
        return (T) result.get();
    }
Get the value corresponding to this request (only available if the request succeeded)
@return the value set in {@link #complete(Object)}
@throws IllegalStateException if the future is not complete or failed
clients/src/main/java/org/apache/kafka/clients/consumer/internals/RequestFuture.java