public void setRecipient(InternalDistributedMember recipient) {
    if (recipients != null) {
      throw new IllegalStateException(
          "Recipients can only be set once");
    }

    recipients = Collections.singletonList(recipient);
  }
Sets the intended recipient of the message. If recipient is Message.ALL_RECIPIENTS
then the
message will be sent to all distribution managers.
geode-core/src/main/java/org/apache/geode/distributed/internal/DistributionMessage.java