My services file (C:\\WINDOWS\\system32\\drivers\\etc\\services) has a bunch of Port to Service mappings:
echo 7/tcp echo 7/udp
What you are looking for is a Java implementation of the Linux getservbyport() system call. Take a look at http://github.com/wmeissner/jnr-netdb. Also, do a Google search for java getservbyport
getservbyport()
java getservbyport