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# Discovery Exceptions (22001 - 22004)

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`DiscoveryException` is a run-time exception that is raised when `DiscoveryManager` is operating.

Format

    EXCEPTION [TOPLINK – error code]: Exception name
    EXCEPTION DESCRIPTION: Message

Discovery Exception

    EXCEPTION [TOPLINK – 22001]: oracle.toplink.exception.DiscoveryException
    EXCEPTION DESCRIPTION: Could not join multicast group.

22001: ERROR_JOINING_MULTICAST_GROUP
  Cause: `DiscoveryManager` failed to join a multicast group due to a `java.io.IOException`: either a `MulticastSocket` could not be created, or the invocation of the `joingGroup` method of the MulticastSocket failed.
  Action: See the generated exception for the root cause.

22002: ERROR_SENDING_ANNOUNCEMENT
  Cause: `DiscoveryManager` failed to inform other services that its service had started up.
  Action: Consider increasing the announcement delay: the amount of time in milliseconds that the service should wait between the time that this remote service is available and a session announcement is sent out to other discovery managers. This may be needed to give some systems more time to post their connections into the naming service. See the `setAnnouncementDelay` method of the `DiscoveryManager`.

22003: ERROR_LOOKING_UP_LOCAL_HOST
  Cause: DiscoveryManager failed to do the lookup of a local host.
  Action: See the generated exception for the root cause.

22004: ERROR_RECEIVING_ANNOUNCEMENT
  Cause: `DiscoveryManager` caught a `java.io.IOException` while blocking for announcements from other `DiscoveryManagers`.
  Action: See the generated exception for the root cause.