为什么新建一个项目就可以访问？而不报404

<?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>Test</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>
  
   <!-- 声明Servlet -->
  <servlet>
  	<!-- servlet的别名 -->
  	<servlet-name>first</servlet-name>
  	<servlet-class>com.imooc.servlet.Test</servlet-class>
  </servlet>
  
  <!-- 将Servlet与URL绑定 -->
  <servlet-mapping>
  	<servlet-name>first</servlet-name>
  	<url-pattern>/hi</url-pattern>
  </servlet-mapping>
  
</web-app>

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 Test 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("返回给浏览器的响应数据为："+html);
		PrintWriter out=response.getWriter();
		out.println(html);
	}
	
}

上面这个是新建的项目，可以访问。下面这个就不行，对比了好久也没看出来哪里不对。

<?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>FistServlet</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>
  
  <!-- 声明Servlet -->
  <servlet>
  	<!-- servlet的别名 -->
  	<servlet-name>first</servlet-name>
  	<servlet-class>com.imooc.servlet.FirstServlet</servlet-class>
  </servlet>
  
  <!-- 将Servlet与URL绑定 -->
  <servlet-mapping>
  	<servlet-name>first</servlet-name>
  	<url-pattern>/hi</url-pattern>
  </servlet-mapping>
</web-app>

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 FirstServlet 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("返回给浏览器的响应数据为："+html);
		PrintWriter out=response.getWriter();
		out.println(html);
	}

}

求解答。谢谢~