Definir DataSource no Tomcat 7

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" version="3.0">
  <display-name>First</display-name>
//servlet, etc
  <resource-ref>
	<res-ref-name>jdbc/banco</res-ref-name>
	<res-type>javax.sql.DataSource</res-type>
	<res-auth>Container</res-auth>
  </resource-ref>
</web-app>

<Context>

	<Resource

	name="jdbc/banco"

	auth="Container"

	type="javax.sql.DataSource"

	username="root"

	password="minhasenha"

	driverClassName="com.mysql.jdbc.Driver"

	url="jdbc:mysql://localhost:3306/jsf" />

</Context>

import java.sql.Connection;

import java.sql.SQLException;



import javax.annotation.Resource;

import javax.sql.DataSource;





public class Conexao{



	@Resource(name="jdbc/banco")

	private DataSource dataSource;

	

	public Connection conectarMysql() throws SQLException{

		

		if(dataSource == null){

			throw new SQLException("DataSource inexistente");

		}

		Connection connection = dataSource.getConnection();

		if(connection == null){

			throw new SQLException("Não há conexão com o banco");

		}		

		return connection;

	}

}