javax.naming.NameNotFoundException 求高手

获取数据库的连接代码
public Connection getConnectionDs(){

    try {
        //初始化上下文
        Context ctx = new InitialContext();
        DataSource das = (DataSource)(ctx.lookup("java:comp/env/news"));
        cont = das.getConnection();
    } catch (NamingException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    } catch (SQLException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }


    return cont;
}
配置文件 tomcat conf目录下的context
<Resource name = "news" 
auth = "Container" type = "javax.sql.DataSource"  
maxActive = "100" maxIdle = "30" maxWait = "10000" 
username = "root" password = "bdqn" 
driverClassName = "com.mysql.jdbc.Driver" url = "jdbc:mysql://127.0.0.1:3306/news"/>

没有找到数据源，估计是数据源设置有问题