我认为我有原因. Tomcat试图防止由于某些特定的java/javax api而导致的内存泄漏，并且sql server驱动程序似乎就是其中之一.如果禁用该功能，它将自动加载驱动程序.要禁用，请如下修改server.xml JreMemoryLeakPreventionListener条目.

I think I got the reason. Tomcat tries to prevent memory leaks due to some particular java/javax apis and it seems that the sql server driver is one of them. If you disable that feature it should load the driver automatically. To disable, modify the server.xml JreMemoryLeakPreventionListener entry as below.

<Listener className="org.apache.catalina.core.JreMemoryLeakPreventionListener" driverManagerProtection="false" />