jakarta.servlet.ServletException: 类com.kang.servlet.HelloServlet不是Servlet

在使用servlet的时候遇到一个报错

jakarta.servlet.ServletException: 类com.kang.servlet.HelloServlet不是Servlet
	org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:542)
	org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92)
	org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:693)
	org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:339)
	org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:374)
	org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65)
	org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:845)
	org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1563)
	org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
	java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
	java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
	org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
	java.lang.Thread.run(Thread.java:748)
根本原因。

java.lang.ClassCastException: com.kang.servlet.HelloServlet cannot be cast to jakarta.servlet.Servlet
	org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:542)
	org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92)
	org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:693)
	org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:339)
	org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:374)
	org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65)
	org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:845)
	org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1563)
	org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
	java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
	java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
	org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)

pom.xml

   <dependency>
            <groupId>javax.servlet</groupId>
            <artifactId>javax.servlet-api</artifactId>
            <version>4.0.1</version>
            <scope>compile</scope>
        </dependency>

这是因为使用了最新的tomcat10，而tomcat10有个最大的变动就是Tomcat 10 m1将JavaEE也换成了Jakarta® EE
Jakarta® EE较以前的JavaEE有一个非常非常重要的更新：包名不再是"javax.servlet.“而是改成了"jakarta.servlet.”

解决方案：将tomcat改完tomcat9 就可以了