is is it necessary to open the database oracle to execute the query
It is necessary to have an open database connection to run a query. You can open one yourself in your servlet, but it's better to obtain one from a connection pool.
Tomcat has a connection pool library that can manage the connections for you and allow the connections to be shared across the entire application. See the Tomcat documentation for more information. [ December 18, 2006: Message edited by: Scott Johnson ]