相关代码：
package com.example.web;
import javax.servlet.*;
import java.io.IOException;
public class DemoServlet implements Servlet {
@Override
public void init(ServletConfig servletConfig) throws ServletException {
}
@Override
public ServletConfig getServletConfig() {
return null;
}
// 在这里处理请求
@Override
public void service(ServletRequest servletRequest, ServletResponse servletResponse) throws ServletException, IOException {
System.out.println("处理请求！");
}
@Override
public String getServletInfo() {
return null;
}
@Override
public void destroy() {
}
}
<?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_4_0.xsd"
version="4.0">
<servlet>
<servlet-name>DemoServlet</servlet-name>
<servlet-class>com.example.web.DemoServlet</servlet-class>
</servlet>
<servlet-mapping>
<!-- 这个时候访问地址为http://port/工程路径/hello -->
<servlet-name>DemoServlet</servlet-name>
<url-pattern>/hello</url-pattern>
</servlet-mapping>
</web-app>
访问地址：http://localhost:8080/web_war/hello出现下面报错
错误信息：
jakarta.servlet.ServletException: 类com.example.web.DemoServlet不是Servlet
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
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ConnectionHandler.process(AbstractProtocol.java:872) org.apache.tomcat.util.net.NioEndpoint
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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
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Worker.run(ThreadPoolExecutor.java:659) org.apache.tomcat.util.threads.TaskThread
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WrappingRunnable.run(TaskThread.java:61)
java.lang.Thread.run(Thread.java:748)
java.lang.ClassCastException: com.example.web.DemoServlet cannot be cast to jakarta.servlet.Servlet
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
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ConnectionHandler.process(AbstractProtocol.java:872) org.apache.tomcat.util.net.NioEndpoint
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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)
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Worker.run(ThreadPoolExecutor.java:659) org.apache.tomcat.util.threads.TaskThread
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WrappingRunnable.run(TaskThread.java:61)
java.lang.Thread.run(Thread.java:748)
报错原因
Spring (and Spring Boot) currently only support JavaEE and not JakartaEE. Which means that it will only run on/with JavaEE compatible servers. Tomcat10 is an implementation of the JakartaEE specification which currently isn’t supported.The only solution is to downgrade to Tomcat 9.
解决方案：
我用的是Tomcat10切换到版本9或以下, 我换成了Tomcat8就能成功了。