使用JAX-RS+Tomcat 9.0.21访问资源时出现404错误求助

环境与问题描述 #

使用JDK 17、Maven 3.9.5、Tomcat 9.0.21学习JAX-RS，通过GlassFish的jersey-quickstart-webapp原型生成项目。构建部署后，访问http://localhost:8080/messenger/webapi/myresource出现404错误，已排查Servlet映射但未找到问题。

项目代码片段 #

index.jsp

<html>
<body>
    <h2>Jersey RESTful Web Application!</h2>
    <p><a href="webapi/myresource">Jersey resource</a>
    <p>Visit <a href="http://jersey.java.net">Project Jersey website</a>
    for more information on Jersey!
</body>
</html>

MyResource.java

package in.net.myproj.practice.javabrains;

import jakarta.ws.rs.GET;
import jakarta.ws.rs.Path;
import jakarta.ws.rs.Produces;
import jakarta.ws.rs.core.MediaType;

/**
 * Root resource (exposed at "myresource" path)
 */
@Path("myresource")
public class MyResource {

    /**
     * Method handling HTTP GET requests. The returned object will be sent
     * to the client as "text/plain" media type.
     *
     * @return String that will be returned as a text/plain response.
     */
    @GET
    @Produces(MediaType.TEXT_PLAIN)
    public String getIt() {
        return "Got it!";
    }
}

web.xml

<?xml version="1.0" encoding="UTF-8"?>
<!-- This web.xml file is not required when using Servlet 3.0 container,
     see implementation details http://jersey.java.net/nonav/documentation/latest/jax-rs.html -->
<web-app version="2.5" xmlns="http://java.sun.com/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd">
    <servlet>
        <servlet-name>Jersey Web Application</servlet-name>
        <servlet-class>org.glassfish.jersey.servlet.ServletContainer</servlet-class>
        <init-param>
            <param-name>jersey.config.server.provider.packages</param-name>
            <param-value>in.net.hrs.practice.javabrains</param-value>
        </init-param>
        <load-on-startup>1</load-on-startup>
    </servlet>
    <servlet-mapping>
        <servlet-name>Jersey Web Application</servlet-name>
        <url-pattern>/webapi/*</url-pattern>
    </servlet-mapping>
</web-app>

pom.xml

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">

    <modelVersion>4.0.0</modelVersion>

    <groupId>in.net.myproj.practice</groupId>
    <artifactId>messenger</artifactId>
    <packaging>war</packaging>
    <version>1.0-SNAPSHOT</version>
    <name>messenger</name>

    <build>
        <finalName>messenger</finalName>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>3.11.0</version>
                <inherited>true</inherited>
                <configuration>
                    <source>17</source>
                    <target>17</target>
                </configuration>
            </plugin>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-war-plugin</artifactId>
                <version>3.4.0</version>
            </plugin>
        </plugins>
    </build>

    <dependencyManagement>
        <dependencies>
            <dependency>
                <groupId>org.glassfish.jersey</groupId>
                <artifactId>jersey-bom</artifactId>
                <version>${jersey.version}</version>
                <type>pom</type>
                <scope>import</scope>
            </dependency>
        </dependencies>
    </dependencyManagement>

    <dependencies>
        <dependency>
            <groupId>org.glassfish.jersey.containers</groupId>
            <artifactId>jersey-container-servlet-core</artifactId>
            <!-- use the following artifactId if you don't need servlet 2.x compatibility -->
            <!-- artifactId>jersey-container-servlet</artifactId -->
        </dependency>
        <dependency>
            <groupId>org.glassfish.jersey.inject</groupId>
            <artifactId>jersey-hk2</artifactId>
        </dependency>
        <!-- uncomment this to get JSON support
        <dependency>
            <groupId>org.glassfish.jersey.media</groupId>
            <artifactId>jersey-media-json-binding</artifactId>
        </dependency>
        -->
    </dependencies>
    <properties>
        <jersey.version>4.0.0-M1</jersey.version>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <war.mvn.plugin.version>3.4.0</war.mvn.plugin.version>
    </properties>
</project>

问题根源与修复方案 #

1. 资源包路径配置不匹配 #

web.xml中jersey.config.server.provider.packages参数指定的包是in.net.hrs.practice.javabrains，但实际MyResource类所在包为in.net.myproj.practice.javabrains，路径不一致导致Jersey无法扫描到资源类。

修复：
修改web.xml中的包路径：

<init-param>
    <param-name>jersey.config.server.provider.packages</param-name>
    <param-value>in.net.myproj.practice.javabrains</param-value>
</init-param>

2. Jersey版本与Tomcat兼容性冲突 #

使用的Jersey 4.0.0-M1是预览版，依赖Jakarta EE 9+规范（API包名jakarta.*），但Tomcat 9仅支持Servlet 4.0（对应Jakarta EE 8，API包名javax.*），存在兼容性问题。

修复：
降级Jersey到支持Jakarta EE 8的稳定版本（如2.41），并调整API导入：

• 修改pom.xml中的版本属性：

<properties>
    <jersey.version>2.41</jersey.version>
    <!-- 其他属性保持不变 -->
</properties>

• 修改MyResource.java中的导入包：

import javax.ws.rs.GET;
import javax.ws.rs.Path;
import javax.ws.rs.Produces;
import javax.ws.rs.core.MediaType;

3. Servlet容器依赖适配优化 #

当前使用的jersey-container-servlet-core是兼容Servlet 2.x的版本，Tomcat 9支持Servlet 4.0，建议使用更适配的jersey-container-servlet：

<dependency>
    <groupId>org.glassfish.jersey.containers</groupId>
    <artifactId>jersey-container-servlet</artifactId>
</dependency>

4. 验证部署上下文路径 #

确认Tomcat中项目的部署上下文路径为messenger，可通过Tomcat管理控制台查看已部署应用的上下文路径，确保访问URL中的/messenger与实际一致。

验证步骤 #

1. 修改配置后执行mvn clean package重新构建项目
2. 将生成的messenger.war部署到Tomcat的webapps目录
3. 启动Tomcat，访问http://localhost:8080/messenger/webapi/myresource，应返回Got it!

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