类型 异常报告
消息 实例化Servlet类[com.imooc.servlet.FirstServlet]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
javax.servlet.ServletException: 实例化Servlet类[com.imooc.servlet.FirstServlet]异常
	org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:544)
	org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:81)
	org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:698)
	org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:364)
	org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:616)
	org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65)
	org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:831)
	org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1629)
	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:750)
根本原因。
java.lang.ClassNotFoundException: com.imooc.servlet.FirstServlet
	org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1372)
	org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1195)
	org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:544)
	org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:81)
	org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:698)
	org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:364)
	org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:616)
	org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65)
	org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:831)
	org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1629)
	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:750)
):注意 主要问题的全部 stack 信息可以在 server logs 里查看

<?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>first</servlet-name>
        <servlet-class>com.imooc.servlet.FirstServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>first</servlet-name>
        <url-pattern>/hi</url-pattern>
    </servlet-mapping>
</web-app>

package com.imooc.servlet;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintWriter;

public class FirstServlet extends HttpServlet {
    @Override
    protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        String name = req.getParameter("name");
        String html = "<h1 style='color:red'>hi," + name + "!</h1><hr>";
        System.out.println("返回给浏览器的响应内容为:" + html);
        PrintWriter out = resp.getWriter();
        out.println(html);
    }
}

相关截图：

第一次可以正常运行，重启tomcat第二次运行就报错了