How to set a datasource in tomcat

It seems a simple thing:
create a context.xml in the PUBLIC-HTML/META-INF folder of the web app.

The content of the context.xml must be something like this:

<?xml version="1.0" encoding="UTF-8"?>
<Context path="/webAppName" docBase="webAppName">
<Resource name="jdbc/DataSourceName" auth="Container"
type="javax.sql.DataSource" driverClassName="oracle.jdbc.OracleDriver"
url="jdbc:oracle:thin:@dataBase:1521:ORCL"
username="user" password="pwd" maxActive="20" maxIdle="10"
maxWait="-1"/>
</Context>