HTTP状态 404 - 未找到

package com.imooc.servlet;

import java.io.IOException;

import java.io.PrintWriter;

import javax.servlet.ServletException;

import javax.servlet.http.HttpServlet;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;

public class first extends HttpServlet{

@Override

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

String name=request.getParameter("name");

String html="<h1 style='color:red'>hi"+name+"</h1><hr/>";

System.out.println(html);

PrintWriter out=response.getWriter();

out.println(html);

}

}

<?xml version="1.0" encoding="UTF-8"?>

<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://xmlns.jcp.org/xml/ns/javaee" xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd" id="WebApp_ID" version="3.1">

  <display-name>FirstServlet</display-name>

  <welcome-file-list>

    <welcome-file>index.html</welcome-file>

    <welcome-file>index.htm</welcome-file>

    <welcome-file>index.jsp</welcome-file>

    <welcome-file>default.html</welcome-file>

    <welcome-file>default.htm</welcome-file>

    <welcome-file>default.jsp</welcome-file>

  </welcome-file-list>

  <servlet>

  <servlet-name>first</servlet-name>

  <servlet-class>com.imooc.servlet.first</servlet-class>

  </servlet>

  <servlet-mapping>

  <servlet-name>first</servlet-name>

  <url-pattern>/hi</url-pattern>

  </servlet-mapping>

</web-app>

​