JXTA in a Nutshell

Name

DiscoveryService

Synopsis

This interface represents the core JXTA discovery service. All peergroups have an implementation of the discovery service, which is used to locate advertisements within the peergroup. The discovery service of a particular peergroup is retrieved via the getDiscoveryService( ) method of the PeerGroup class.

Applications keep a persistent cache of previously discovered advertisements. In the core Java bindings, the persistent cache is held in the filesystem (in the cm directory) and survives between runs of the application; in other implementations, the cache may exist only while the device is on. Applications look for advertisements within the cache by using the getLocalAdvertisements( ) method. The cache is emptied by the flushAdvertisements( ) method.

Applications look for uncached advertisements by using the getRemoteAdvertisements( ) method. This sends out the discovery message using the PDP and sets up a background daemon thread that listens for responses. The background thread places those responses in the local cache where they may be retrieved by the getLocalAdvertisements( ) method. Alternately, a discovery event listener may be registered with the discovery service by calling the addDiscoveryListener( ) method, in which case the listener will be called whenever a new advertisement is discovered.

The publish( ) method places a new advertisement in the local cache; the remotePublish( ) method provides a new advertisement available ...