[FIXED] Error 500 occurs when accessing the servlet class

Issue

When trying to launch the application, error 500 (HTTP Status 500 – Internal Server Error) appears when it comes to accessing the ControllerServlet, the code of which is presented below

import javax.servlet.ServletException;
import javax.servlet.http.*;
import java.io.IOException;

public class ControllerServlet extends HttpServlet {

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        if (req.getParameter("x") == null || req.getParameter("y") == null || req.getParameter("r") == null || req.getParameter("key") == null) {
            req.getServletContext().getRequestDispatcher("/index.jsp").forward(req, resp);
        }
        else{
            getServletContext().getNamedDispatcher("AreaChecker").forward(req, resp);
        }
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        if (req.getParameter("key").equals("update")) {
            getServletContext().getNamedDispatcher("AreaChecker").forward(req, resp);
        }
        else{
            req.getServletContext().getNamedDispatcher("Controller").forward(req, resp);
        }
    }

} 

Text of error:

Type Exception Report

Message Класс [com.example.ControllerServlet] не является сервлетом

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

Exception

jakarta.servlet.ServletException: Класс [com.example.ControllerServlet] не является сервлетом 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:1705) 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.base/java.lang.Thread.run(Thread.java:829) Root Cause

java.lang.ClassCastException: class com.example.ControllerServlet cannot be cast to class jakarta.servlet.Servlet (com.example.ControllerServlet is in unnamed module of loader org.apache.catalina.loader.ParallelWebappClassLoader @7abda5a1; jakarta.servlet.Servlet is in unnamed module of loader java.net.URLClassLoader @37afeb11) 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:1705) 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.base/java.lang.Thread.run(Thread.java:829)

Version of Tomcat: 10.0.14

My question is: how to avoid this error and what needs to be fixed?

Solution

The issue is here:

java.lang.ClassCastException: class com.example.ControllerServlet cannot be cast to class jakarta.servlet.Servlet

here:

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

and here:

Version of Tomcat: 10.0.14

You have a javax servlet in a servlet container that implements version 5 of the servlet specification which is now in the jakarta namespace.

You need to extend your servlet from the jakarta packages, not javax.

See the following links for more details:

• https://tomcat.apache.org/whichversion.html
• https://en.wikipedia.org/wiki/Jakarta_Servlet
• https://dzone.com/articles/jakarta-ee-without-javax-the-world-wont-end-this-time-either

Answered By - Bogdan
Answer Checked By - Cary Denson (JavaFixing Admin)