tomcat - jakarta.servlet.ServletException: Class [com.practice.MyServlet] is not a Servlet

Question

I am beginner to working with servlet.
I am creating a servlet and but after running that i am getting error
Can anyone help me to resolve this.

Error

Type Exception Report

Message Class [com.practice.MyServlet] is not a Servlet

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

Exception

jakarta.servlet.ServletException: Class [com.practice.MyServlet] is not a Servlet org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:543) org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92) org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:682) org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:332) org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:374) org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65) org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:859) org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1568) 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) Root Cause

java.lang.ClassCastException: com.practice.MyServlet cannot be cast to jakarta.servlet.Servlet org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:543) org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92) org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:682) org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:332) org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:374) org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65) org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:859) org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1568) 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) Note The full stack trace of the root cause is available in the server logs.

Click here to see the Project directory

MyServlet.java

package com.practice;

import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.*;
import javax.servlet.http.*;
/**
 *
 * @author admin
 */
public class MyServlet extends HttpServlet {
    
    @Override
    public void doGet(HttpServletRequest request,HttpServletResponse response)throws ServletException, IOException
    {
        PrintWriter out=response.getWriter();
        response.setContentType("test/html");
        out.print("<h1>This is get method of my servlet</h1>");
    }
}

Web.xml

<?xml version="1.0" encoding="UTF-8"?>

<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
     xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd"
     version="3.1">
    
    <servlet>
        <servlet-name>myservlet</servlet-name>
        <servlet-class>com.practice.MyServlet</servlet-class>
    </servlet>
    
    <servlet-mapping>
        <servlet-name>myservlet</servlet-name>
        <url-pattern>/myservlet</url-pattern>
    </servlet-mapping>
    
    <session-config>
        <session-timeout>
            30
        </session-timeout>
    </session-config>
</web-app>

Answer 1

You're basically physically including Tomcat 9.x (Servlet 4.0) specific JAR file in WAR and then writing/compiling code against Tomcat 9.x (Servlet 4.0) or older and then then deploying the WAR to Tomcat 10.x (Servlet 5.0) or newer. This is not the correct approach at all.

Since Tomcat 10.x (Servlet 5.0) the javax.* package has been renamed to jakarta.* package.

In other words, please make sure that you don't randomly put JAR files of a different server in your WAR such as tomcat-servlet-api-9.0.4.jar. This will only cause trouble. Remove it altogether and edit the imports of your servlet class from

import javax.servlet.*;
import javax.servlet.http.*;

to

import jakarta.servlet.*;
import jakarta.servlet.http.*;

While at it, please also make sure that the root element of the web.xml is declared conform the Servlet API version of the target server, which is in case of Tomcat 10.x thus Servlet 5.0 (and thus not Servlet 3.1 which basically matches Tomcat 8.0).

<web-app
    xmlns="https://jakarta.ee/xml/ns/jakartaee"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="https://jakarta.ee/xml/ns/jakartaee https://jakarta.ee/xml/ns/jakartaee/web-app_5_0.xsd"
    version="5.0"
>
    <!-- Config here. -->
</web-app>

See also:

• Tomcat versions
• Tomcat 9 casting servlets to javax.servlet.Servlet instead of jakarta.servlet.http.HttpServlet