com.neeve.toa.spi
Interface ChannelJoinProvider

public interface ChannelJoinProvider

A ChannelJoinProvider can be used to specify the whether or not a channel should be joined.

Normally a TopicOrientedApplication will automatically join a channel if it finds an EventHandler for a message type that is mapped to the channel in a service definition. An application may provide a ChannelJoinProvider to override this behavior.

See Also:

TopicOrientedApplication messaging configuration

Method Summary

TopicOrientedApplication.ChannelJoin

getChannelJoin(ToaService service, ToaServiceChannel channel) Indicates whether or not a channel should be joined.

Method Detail

getChannelJoin

TopicOrientedApplication.ChannelJoin getChannelJoin(ToaService service,
                                                    ToaServiceChannel channel)

Indicates whether or not a channel should be joined.

Return Values

A ChannelJoinProvider may return a TopicOrientedApplication.ChannelJoin value to indicate whether or not a channel should be joined:

A value of Default or null indicates that the provider has no opinion and will defer to the default behavior of Hornet or other ChannelJoinProviders
• A value of Join indicates that the the channel should be joined even if there is no EventHandler handler registered for any of the channel's types. Overriding the default behavior to join a channel should be rare, since applications should not be attracting messages without handlers or sending messages on channels other than those that they are mapped to in a service definition.
• NoJoin indicates that even if there is a message handler defined for a type mapped to the channel, that the channel should not be joined.

Otherwise, if there isn't a handler for the message and no ChannelJoinProvider returns a value, but the channel is preconfigured for the application via DDL configuration then the preconfigured value for join will be used. In summary, the precendence for determining channel join is as follows:

• ChannelJoinProvider returning non Default join value.
• Presence of a handler for a message mapped to the channel in the service
• Preconfigured value in configuration DDL for the application
• ... if none of the above then default is not to join.

ChannelJoinProvider Conflicts

It is illegal for one ChannelJoinProvider returns Join and another to return NoJoin. The application will fail to start in such a case.

Parameters:

service - The service that defined the channel.

channel - The channel.

Returns:

A value indicating whether or not the channel should be joined.

See Also:

TopicOrientedApplication messaging configuration