使用的是注釋,metadata-complete="true"，下面是web.xml<?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" metadata-complete="true" version="3.1">? <absolute-ordering/>? <display-name>web</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></web-app>寫個打印語句也報404package com.it66.session;import java.io.IOException;import javax.servlet.ServletException;import javax.servlet.annotation.WebServlet;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;/**?* Servlet implementation class SessionServlet?*/@WebServlet("/SessionServlet")public class SessionServlet extends HttpServlet { private static final long serialVersionUID = 1L; protected void service(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { System.out.println("SessionServlet"); }}求大佬幫解決