Servlet访问出现404错误求助（IntelliJ+Tomcat9+Maven+Servlet5）

环境：IntelliJ IDEA、Tomcat 9、Maven、Servlet 5

主页可正常访问，但两个测试Servlet均返回404错误。两个Servlet分别为：一个仅用@WebServlet注解未在web.xml映射，另一个同时配置注解和xml映射，均无法访问。

错误信息 #

HTTP Status 404 – Não Encontrado
Type Status Report

Description The origin server did not find a current representation for the target resource or is not willing to disclose that one exists.

Apache Tomcat/9.0.84

相关代码 #

Servlet 1（HelloServlet） #

package br.com.caelum.fj21agenda;

import java.io.*;
import jakarta.servlet.ServletException;
import jakarta.servlet.http.*;
import jakarta.servlet.annotation.*;

@WebServlet("/servlet")
public class HelloServlet extends HttpServlet {

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


        PrintWriter out = response.getWriter();

        //Escreve o texto
        out.println("<html>");
        out.println("<body>");
        out.println("Primeira Servlet ^^ yay");
        out.println("</body>");
        out.println("</html>");

    }
}

Servlet 2（HelloServlet2） #

package br.com.caelum.fj21agenda;

import jakarta.servlet.ServletException;
import jakarta.servlet.http.HttpServlet;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.util.HashMap;
import java.util.Map;
import jakarta.servlet.annotation.WebServlet;

@WebServlet("/hello")
public class HelloServlet2 extends HttpServlet {

    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // Preprocess request: we actually don't need to do any business stuff, so just display JSP.
        request.getRequestDispatcher("/WEB-INF/hello.jsp").forward(request, response);
    }

    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // Postprocess request: gather and validate submitted data and display the result in the same JSP.

        // Prepare messages.
        Map<String, String> messages = new HashMap<>();
        request.setAttribute("messages", messages);

        // Get and validate name.
        String name = request.getParameter("name");
        if (name == null || name.trim().isEmpty()) {
            messages.put("name", "Please enter name");
        } else if (!name.matches("\\p{Alnum}+")) {
            messages.put("name", "Please enter alphanumeric characters only");
        }

        // Get and validate age.
        String age = request.getParameter("age");
        if (age == null || age.trim().isEmpty()) {
            messages.put("age", "Please enter age");
        } else if (!age.matches("\\d+")) {
            messages.put("age", "Please enter digits only");
        }

        // No validation errors? Do the business job!
        if (messages.isEmpty()) {
            messages.put("success", String.format("Hello, your name is %s and your age is %s!", name, age));
        }

        request.getRequestDispatcher("/WEB-INF/hello.jsp").forward(request, response);
    }

}

web.xml #

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="https://jakarta.ee/xml/ns/jakartaee"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="https://jakarta.ee/xml/ns/jakartaee https://jakarta.ee/xml/ns/jakartaee/web-app_5_0.xsd"
         version="5.0">

    <servlet>
        <servlet-name>HelloServlet</servlet-name>
        <servlet-class>br.com.caelum.fj21agenda.HelloServlet</servlet-class>
    </servlet>

    <servlet-mapping>
        <servlet-name>HelloServlet</servlet-name>
        <url-pattern>/servlet</url-pattern>
    </servlet-mapping>

</web-app>

index.html #

<!DOCTYPE html>
<html lang="en">
    <head>
        <meta charset="UTF-8">
        <title>Projeto Fj21-agenda </title>
    </head>
    <body>
        <h1>Primeira Pagina YAYY</h1>
    </body>
</html>

文件结构说明 #

项目遵循Maven标准结构：

• Servlet类位于src/main/java/br/com/caelum/fj21agenda目录下
• Web资源位于src/main/webapp目录下，包含index.html和WEB-INF目录

排查与解决步骤 #

1. 版本兼容性修复
   Servlet 5属于Jakarta EE 9规范，使用jakarta.servlet包；而Tomcat 9仅支持到Servlet 4（Java EE 8），对应javax.servlet包，这是核心冲突点。

   • 方案1：降级Servlet依赖到4.x，将代码中jakarta.servlet替换为javax.servlet，web.xml改用Servlet 4.0的schema
   • 方案2：升级Tomcat到10.x及以上版本，适配Jakarta EE 9+规范

2. 确认注解扫描状态
   检查web.xml中是否存在<metadata-complete="true">属性，该属性会关闭注解自动扫描，若存在则删除。Servlet 3+默认开启注解扫描，无需额外配置。

3. 修正Maven依赖范围
   Servlet API依赖需设置为provided，避免打包到war包中与Tomcat自带API冲突：

   <dependency>
       <groupId>jakarta.servlet</groupId>
       <artifactId>jakarta.servlet-api</artifactId>
       <version>5.0.0</version>
       <scope>provided</scope>
   </dependency>
   

4. 验证访问路径
   访问Servlet时需加上项目上下文路径，例如项目部署上下文为/fj21agenda，则正确访问地址为：

   • http://localhost:8080/fj21agenda/servlet
   • http://localhost:8080/fj21agenda/hello

5. 检查IDEA部署配置
   在IntelliJ IDEA的Run/Debug配置中，确认Tomcat的Deployment选项里：

   • 项目已添加到部署列表
   • Application context设置与访问路径匹配

6. 清理重建项目
   执行Maven命令clean和package，清理编译缓存后重新部署到Tomcat，排除编译或打包异常。

内容的提问来源于stack exchange，提问作者SchattenRaff