写了一个简单的servlet，部署到tomcat，在cmd中直接启动遇到报错，以下贴上三条我觉得可能比较重要的提示信息，求解，谢谢！
27-Feb-2016 22:25:10.849 SEVERE [localhost-startStop-1] org.apache.catalina.core.ContainerBase.addChildInternal ContainerBase.addChild: start:
org.apache.catalina.LifecycleException: Failed to start component [StandardEngine[Catalina].StandardHost[localhost].StandardContext[]]
Caused by: java.lang.IllegalArgumentException: Invalid null in servlet mapping
27-Feb-2016 22:25:10.852 SEVERE [localhost-startStop-1] org.apache.catalina.startup.HostConfig.deployDirectory Error deploying web application directory C:\javawork\testservlet\apache-tomcat-8.0.30-windows-x64\apache-tomcat-8.0.30\webapps\ROOT
java.lang.IllegalStateException: ContainerBase.addChild: start: org.apache.catalina.LifecycleException: Failed to start component [StandardEngine[Catalina].StandardHost[localhost].StandardContext[]]
另外，下面是我的web.xml文件配置：
UseServlet
UseServlet
UseServlet
/UseServlet
