jakarta.servlet.ServletException:类[com.practice.MyServlet]不是Servlet

Question

我是使用servlet的初学者。

我正在创建一个servlet，但是在运行之后，我得到了错误。

有人能帮我解决这个问题吗。

误差

类型异常报告 消息类com.practice.MyServlet不是Servlet 描述服务器遇到的意外情况，使其无法完成请求。 异常 jakarta.servlet.ServletException:类com.practice.MyServlet不是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(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)的根本原因 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) java.lang.ClassCastException:不能将com.practice.MyServlet转换为jakarta.servlet.Servlet java.lang.ClassCastException 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)注意，根本原因的全部堆栈跟踪在服务器日志中可用。

单击此处查看Project目录

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

您基本上在WAR中包括Tomcat 9.x (Servlet 4.0)特定的JAR文件，然后针对Tomcat 9.x (Servlet 4.0)或更高版本编写/编译代码，然后将WAR部署到Tomcat 10.x (Servlet 5.0)或更新版本。这根本不是正确的方法。

从Tomcat10.x(Servlet5.0)开始，javax.*包被重命名为jakarta.*包。

换句话说，请确保在WAR (如tomcat-servlet-api-9.0.4.jar )中不要随意放置不同服务器的JAR文件。这只会引起麻烦。删除它并编辑servlet类的导入。

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

至

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

同时，还请确保声明了web.xml的根元素符合目标服务器的Servlet版本，这是Tomcat10.x的Servlet5.0(因此不是Servlet3.1，基本上与Tomcat8.0相匹配)。

<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>

另请参阅：

• Tomcat版本
• Tomcat 9将servlet转换为javax.servlet.Servlet而不是jakarta.servlet.http.HttpServlet