JDBC keep alive issue

Hi experts,

I have a program running like a daemon, which analyze data and write to postgresql 9.1 on centos 5.8. There is only one
connectionbetween my program and the postgresql database, and I hope the connection may keep alive all the time. But I
failed,the connection will be reset after idle for about 2 hours. 

jdbc driver: 9.1-901, connection url has parameter tcpKeepAlive=true;
postgresql:9.1, keep alive related settings use default values(commented);
centos 5.8 64bit, net.ipv4.tcp_keepalive_intvl = 75, probes = 9, time = 7200.

There is no firewall or any other device which behaves force idle connection cleanup.

Am I missing some configurations? What's the right way to keep a long time connection?