[Solved] Tomcat10 Error: jakarta.servlet.ServletException: Class com.kuang.servlet.HelloServlet is not a servlet

 Class com.kuang.servlet.HelloServlet is not a servlet

Description The server encountered an unexpected condition that prevented it from fulfilling the request.

exception

jakarta.servlet.ServletException: Class com.kuang.servlet.HelloServlet is not a servlet
    org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:541)
    org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92)
    org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:690)
    org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:353)
    org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:382)
    org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65)
    org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:872)
    org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1695)
    org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
    org.apache.tomcat.util.threads.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1191)
    org.apache.tomcat.util.threads.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:659)
    org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
    java.lang.Thread.run(Thread.java:748)
Reason.

java.lang.ClassCastException: com.kuang.servlet.HelloServlet cannot be cast to jakarta.servlet.Servlet
    org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:541)
    org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92)
    org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:690)
    org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:353)
    org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:382)
    org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65)
    org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:872)
    org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1695)
    org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
    org.apache.tomcat.util.threads.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1191)
    org.apache.tomcat.util.threads.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:659)
    org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
    java.lang.Thread.run(Thread.java:748)

This is because the latest Tomcat 10 is used, and the biggest change in the latest Tomcat 10 is that Tomcat 10 m1 replaces JavaEE with Jakarta® EE

Jakarta® EE has a very, very important update over the previous JavaEE: the package name is no longer “javax.servlet”. Instead, it has been changed to “jakarta.servlet”

The first solution: downgrade Tomcat 10 to Tomcat 9

The second solution: continue to use Tomcat 10

Import the correct dependencies

<!-- https://mvnrepository.com/artifact/jakarta.servlet/jakarta.servlet-api -->
<dependency>
    <groupId>jakarta.servlet</groupId>
    <artifactId>jakarta.servlet-api</artifactId>
    <version>5.0.0</version>
    <scope>provided</scope>
</dependency>

<!-- https://mvnrepository.com/artifact/jakarta.servlet.jsp/jakarta.servlet.jsp-api -->
<dependency>
    <groupId>jakarta.servlet.jsp</groupId>
    <artifactId>jakarta.servlet.jsp-api</artifactId>
    <version>3.0.0</version>
    <scope>provided</scope>
</dependency>

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