I had a Tomcat& all done according to the tutorial; Used to the environment, the tutorial is as follows:
https://blog.csdn.net/woolceo/article/details/509205
Because of poor old version of the tutorial, and JDBC connection configuration of the tutorial teaching page connection failure, can't open, so use of the new version, configure the environment for: sqlserver2014 enterprise edition, tomcat8.5 installation version not configure the environment variables, because a lot of online said that the version without configuration, also can normal open the test page, jdk7.0 version installation environment variable configuration from other tutorials, but web page to a tip:

Has won the DataSource.
Java. SQL. SQLException: always create a JDBC driver of class 'for the connect URL' null '

Why is this? Where is I lack of something or inappropriate configuration? Consult! Thank you very much!