Servletle类实例化错误

 异常报告

消息 实例化Servlet类[com.kun.HelloWorld]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[com.kun.HelloWorld]异常
	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:690)
	org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:353)
	org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:374)
	org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65)
	org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:870)
	org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1696)
	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)
根本原因。

java.lang.NoClassDefFoundError: javax/servlet/http/HttpServlet
	java.lang.ClassLoader.defineClass1(Native Method)
	java.lang.ClassLoader.defineClass(ClassLoader.java:756)
	java.security.SecureClassLoader.defineClass(SecureClassLoader.java:142)
	org.apache.catalina.loader.WebappClassLoaderBase.findClassInternal(WebappClassLoaderBase.java:2470)
	org.apache.catalina.loader.WebappClassLoaderBase.findClass(WebappClassLoaderBase.java:866)
	org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1370)
	org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1224)
	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:690)
	org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:353)
	org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:374)
	org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65)
	org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:870)
	org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1696)
	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)
根本原因。

java.lang.ClassNotFoundException: javax.servlet.http.HttpServlet
	org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1401)
	org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1224)
	java.lang.ClassLoader.defineClass1(Native Method)
	java.lang.ClassLoader.defineClass(ClassLoader.java:756)
	java.security.SecureClassLoader.defineClass(SecureClassLoader.java:142)
	org.apache.catalina.loader.WebappClassLoaderBase.findClassInternal(WebappClassLoaderBase.java:2470)
	org.apache.catalina.loader.WebappClassLoaderBase.findClass(WebappClassLoaderBase.java:866)
	org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1370)
	org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1224)
	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:690)
	org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:353)
	org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:374)
	org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65)
	org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:870)
	org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1696)
	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 主要问题的全部 stack 信息可以在 server logs 里查看

Apache Tomcat/10.0.4

出现这个问题的原因是tomcat 10中的servlet-api与maven中导入的servlet-api依赖不兼容

最后我把javax.servlet-api依赖改成下面这个

<dependency>
     <groupId>jakarta.servletgroupId>
     <artifactId>jakarta.servlet-apiartifactId>
     <version>5.0.0-M1version>
     <scope>providedscope>
dependency>

同时 ，java源文件记得修改 导入的 包是jakarta.servlet

import jakarta.servlet.ServletException;
import jakarta.servlet.annotation.WebServlet;
import jakarta.servlet.http.HttpServlet;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintWriter;

@WebServlet(name = "HelloWorld")
public class HelloWorld extends HttpServlet {
    private String message;

    public void init() throws ServletException
    {
        // 执行必需的初始化
        message = "Hello World";
    }


    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // 设置响应内容类型
        response.setContentType("text/html");

        // 实际的逻辑是在这里
        PrintWriter out = response.getWriter();
        out.println("
" + message + "
");
    }
}

最后运行idea，并在浏览器 地址栏输入

http://localhost:8080/JavaServlet_maven_war_exploded/HelloWorld

运行结果

参考链接

https://www.cnblogs.com/why-Fighting/p/14753108.html