maven与jar包的冲突问题&&依赖的作用域

错误一描述

java.lang.LinkageError:
loader constraint violation: loader (instance of org/apache/jasper/servlet/JasperLoader) previously initiated loading for a different type with name "javax/servlet/http/HttpServletRequest "
直白的说，tomcat的和javax.servlet加载同名jar包发生了冲突

解决方法是：让javax.servlet不发布到tomcat中，只在编译时生效即可，这时便需要使用scope标签，限制作用域。

错误二描述

Servlet.service() for servlet [jsp] in context with path [] threw exception [java.lang.NullPointerException] with root cause

解决方法同上