servlet3.0以后可以不用web.xml配置了

AbstractDispatcherServletInitializer

注意：删除了web.xml会报错，web.xml is missing and <failOnMissingWebXml> is set to true，解决如下

<plugin>
　　<groupId>org.apache.maven.plugins</groupId>
    <artifactId>maven-war-plugin</artifactId>
    <version>3.0.0</version>
    <configuration>
       <failOnMissingWebXml>false</failOnMissingWebXml>
    </configuration>
</plugin>