继承了HttpServlet却依然报 Class x.x.x is not a Servlet 问题

1 问题解决办法

pom文件中，servlet-api未添加scope导致。因为在tomcat中同样存在servlet-api包，两者会发生冲突；避免冲突的方式，就是给pom中的servlet-api添加scope，值为provided，使pom中的servlet-api只在编译和测试时有效，而在运行时会无效；
以下为我所添加的依赖：

<dependency>
            <groupId>javax.servlet</groupId>
            <artifactId>servlet-api</artifactId>
            <version>3.0-alpha-1</version>
            <scope>provided</scope>
        </dependency>

参考链接：
关于maven依赖中的provided使用
provided范围maven_maven依赖范围

2 附mvc配置tomcat插件时所需pom.xml

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>org.example</groupId>
    <artifactId>enjoy-servlet3</artifactId>
    <version>1.0-SNAPSHOT</version>
    <packaging>war</packaging>

    <dependencies>
        <dependency>
            <groupId>javax.servlet</groupId>
            <artifactId>javax.servlet-api</artifactId>
            <version>3.1.0</version>
            <scope>provided</scope>
        </dependency>

        <dependency>
            <groupId>org.apache.tomcat.embed</groupId>
            <artifactId>tomcat-embed-core</artifactId>
            <version>9.0.14</version>
            <scope>provided</scope>
        </dependency>
    </dependencies>
    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.tomcat.maven</groupId>
                <artifactId>tomcat7-maven-plugin</artifactId>
                <version>2.2</version>
                <configuration>
                    <!--访问端口-->
                    <port>8081</port>
                    <!--访问项目前缀路径-->
                    <path>/enjoy-servlet3</path>
                    <uriEncoding>UTF-8</uriEncoding>
                    <server>tomcat7</server>
                </configuration>
            </plugin>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>3.3</version>
                <configuration>
                    <source>1.8</source>
                    <target>1.8</target>
                </configuration>
            </plugin>
        </plugins>
    </build>
</project>