You can increase the connection pool size in JBoss application server in simple three steps.
1. Figure out the datasource.xml from JBOSS_HOME/SERVER_INSTANCE/deploy. In case of Oracle the file will be named as oracle-ds.xml.
2. Add below given tags into the xxxx-ds.xml file.
3. Restart the JBoss application server.
You can verify the pool size in JMX console uder jboss.jca ManagedConnectionPool section.