You can click on the link TAF in the above post.

I don't have experience with it but know that you can specify multiple addresses under one TNS-alias. Sometimes an oracle connection manager is used.

If the first address is barred the Oracle-Net layer connects to the second address to the application (but doesn't recover lost work)

The mechanism is quite transparent as you only have one tns-alias for the application to connect to.

You need the full OCI-driver. Another link for java