*类型 异常报告
消息 实例化Servlet类[HelloServlet]异常
描述 服务器遇到一个意外的情况，阻止它完成请求。
例外情况
jakarta.servlet.ServletException: 实例化Servlet类[HelloServlet]异常
	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.lang.Thread.run(Thread.java:748)
根本原因。
java.lang.ClassNotFoundException: HelloServlet
	org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1444)
	org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1252)
	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.lang.Thread.run(Thread.java:748)
):注意 主要问题的全部 stack 信息可以在 server logs 里查看*

记录一下在测试servlet时候遇到的一个错误

环境信息

Apache Tomcat/10.0.14
jdk8

HelloServlet.java 

importjakarta.servlet.*;importjava.io.IOException;publicclassHelloServletimplementsServlet{publicvoidinit(ServletConfig config)throwsServletException{}publicvoidservice(ServletRequest request,ServletResponse response)throwsServletException,IOException{System.out.println("Hello,servlet!");}publicvoiddestroy(){}publicStringgetServletInfo(){return"";}publicServletConfiggetServletConfig(){returnnull;}}
<?xml version="1.0" encoding="UTF-8"?><!--
  Licensed to the Apache Software Foundation (ASF) under one or more
  contributor license agreements.  See the NOTICE file distributed with
  this work for additional information regarding copyright ownership.
  The ASF licenses this file to You under the Apache License, Version 2.0
  (the "License"); you may not use this file except in compliance with
  the License.  You may obtain a copy of the License at
      
  Unless required by applicable law or agreed to in writing, software
  distributed under the License is distributed on an "AS IS" BASIS,
  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  See the License for the specific language governing permissions and
  limitations under the License.
--><web-appxmlns=""xmlns:xsi=""xsi:schemaLocation=""version="5.0"metadata-complete="true"><servlet><servlet-name>a</servlet-name><servlet-class>HelloServlet</servlet-class></servlet><servlet-mapping><servlet-name>a</servlet-name><url-pattern>/hello</url-pattern></servlet-mapping></web-app>

有人建议将class文件打包放到classes中，实际上不打包也可以只是在xml中要声明对应的路径 

<servlet-class>HelloServlet</servlet-class>

注意文件路径不要放错 

webapps/[your project]/WEB-INF/classes/HelloServlet.class

最后先启动Tomcat再进入目标网页
project]/hello