"Invalid number format for port number" error when connecting to Oracle database

Issue

Our application couldn't connect to Oracle database.
We see errors like below in server.log:

13-04-2016 21:06:47,020 WARN  [org.jboss.jca.core.connectionmanager.pool.strategy.OnePool] (ajp-/192.168.0.1:10309-32) IJ000604: Throwable while attempting to get a new connection: null: javax.resource.ResourceException: Could not create connection
......
Caused by: java.sql.SQLRecoverableException: Erro de ES: Invalid number format for port number
    at oracle.jdbc.driver.T4CConnection.logon(T4CConnection.java:458)
......
Caused by: oracle.net.ns.NetException: Invalid number format for port number
    at oracle.net.resolver.AddrResolution.resolveSimple(AddrResolution.java:512)