JNDI连接oracle数据库

tomcat里的
context.xml
配置<Resource
name="con"
auth="Container"
type="javax.sql.DataSource"

maxActive="100"
maxIdle="30"
maxWait="10000"

username="system"
password="ok"
driverClassName="oracle.jdbc.driver.OracleDriver"
url="jdbc:oracle:thin:@localhost:1521:orcl"
/>
报错 Cannot create JDBC driver of class '' for connect URL 'null'