For starters I would make sure that the firewall (iptables) isn't an issue. You can confirm with this command on the RPi:
$ iptables -L Chain INPUT (policy ACCEPT) target prot opt source destination Chain FORWARD (policy ACCEPT) target prot opt source destination Chain OUTPUT (policy ACCEPT) target prot opt source destination
If the firewall looks OK (as above), then start your Java application, and confirm with this command that it's listening on the correct port:
$ netstat -anpt Active Internet connections (servers and established) Proto Recv-Q Send-Q Local Address Foreign Address State PID/Program name tcp 0 0 127.0.0.1:9090 0.0.0.0:* LISTEN 970/xbmc.bin tcp 0 0 0.0.0.0:80 0.0.0.0:* LISTEN 970/xbmc.bin tcp 0 0 0.0.0.0:22 0.0.0.0:* LISTEN 936/sshd tcp 0 0 0.0.0.0:445 0.0.0.0:* LISTEN 1086/smbd tcp 0 0 192.168.1.85:22 192.168.1.20:34971 ESTABLISHED 6762/0 tcp 0 0 :::53 :::* LISTEN 829/connmand tcp 0 0 :::22 :::* LISTEN 936/sshd tcp 0 0 :::445 :::* LISTEN 1086/smbd
This command shows which IP address and port each daemon is listening on. For example, the following line:
tcp 0 0 0.0.0.0:80 0.0.0.0:* LISTEN 970/xbmc.bin
Shows a process (xbmc.bin), whose process ID is 970, is listening on port 80, on all the interfaces (0.0.0.0). The last bit "all interfaces" means that if there are multiple network interfaces (ethernet, wifi, etc.) that the daemon will accept connections from any of them.
If it just said an IP address such as 192.168.1.10, then the daemon would only accept connections from the interface that had that IP address assigned to it.
One last thing to note, the types of connections that the above daemon will accept are TCP. The other type is UDP, which this daemon would not accept.
