访问servlet时出现500错误class

Question

尝试启动应用程序时，在访问 ControllerServlet 时出现错误 500（HTTP 状态 500 – 内部服务器错误），其代码如下所示


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：

类型异常报告

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

说明服务器遇到意外情况，无法完成请求。

异常

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: class com.example.ControllerServlet 无法转换为 class jakarta.servlet.Servlet （com.example.ControllerServlet 在加载程序 [=76 的未命名模块中=] @7abda5a1; jakarta.servlet.Servlet 在加载程序的未命名模块中 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)

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

问题在这里：

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

此处：

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

这里：

Version of Tomcat: 10.0.14

您在 servlet 容器中有一个 javax servlet，它实现了现在位于 jakarta 命名空间中的 servlet 规范版本 5。

您需要从 jakarta 包中扩展您的 servlet，而不是 javax。

有关详细信息，请参阅以下链接：

访问servlet时出现500错误class

Error 500 occurs when accessing the servlet class

java

servlets

get

request