TomP2P 5 Beta 2 just released. Check out the latest beta version.
I recommend to switch from TomP2P 4 to TomP2P 5 as TomP2P 4 will not be maintained anymore. Please change your pom.xml to:
<dependency>
<groupId>net.tomp2p</groupId>
<artifactId>tomp2p-core</artifactId>
<version>5.0-Beta2</version>
</dependency>
Many bugfixes, improved routing with RTT sorting (experimental), inital support for hole punching and push notifications.