访问 servlet 类时出现错误 500

Question

在尝试启动应用程序时，访问ControllerServlet时出现错误500（HTTP Status 500 – Internal Server Error），代码如下所示

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);
        }
    }

} 

错误文本：

键入异常报告

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

描述服务器遇到了一个意外情况，导致它无法完成请求。

例外

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) 根本原因

java.lang.ClassCastException：com.example.ControllerServlet 类无法转换为 jakarta.servlet.Servlet 类（com.example.ControllerServlet 位于加载器 org.apache.catalina.loader.ParallelWebappClassLoader @7abda5a1 的未命名模块中；jakarta .servlet.Servlet 位于加载程序 java.net.URLClassLoader @37afeb11 的未命名模块中） 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)

Tomcat 版本：10.0.14

我的问题是：如何避免这个错误以及需要修复什么？

Answer 1

问题就在这里：

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

这里：

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

这里：

Tomcat 版本：10.0.14

您在 servlet 容器中有一个 javax servlet，该容器实现了 servlet 规范的第 5 版，该规范现在位于 jakarta 命名空间中。

您需要从 jakarta 包而不是 javax 扩展您的 servlet。

查看以下链接了解更多详情：

• 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