manager.setUseDefaultSeeds(true);

forums.java.net上的一篇帖子
http://forums.java.net/jive/thread.jspa?threadID=31823&tstart=15

Using public Rdvs and Relays, provided by JXTA community was the default setting for JXSE 2.4.1 tutorial. This is changed for JXSE 2.5 to reduce the traffic!

Both nodes (DiscoveryServer, DiscoveryClient) of your jxta network must be known to a Rdv (and to relay too, if they are behind NAT/firewall). The easiest way for that:

In constructors of classes, representing the client and server, before call to manager.startNetwork() add the following statement:
manager.setUseDefaultSeeds(true);