Spring官方REST示例运行返回404 Not Found错误求助

问题描述 #

按照Spring官方REST服务示例步骤操作，使用Postman发送GET请求访问/greeting路径时返回404错误：

"timestamp": "2023-01-04T09:23:03.965+00:00",
"status": 404,
"error": "Not Found",
"message": "No message available",
"path": "/greeting"

项目代码文件如下：

Greeting.java

package com.example.restservice;

public class Greeting {

    private final long id;
    private final String content;

    public Greeting(long id, String content) {
        this.id = id;
        this.content = content;
    }

    public long getId() {
        return id;
    }

    public String getContent() {
        return content;
    }
}

GreetingController.java

package com.example.restservice;

import java.util.concurrent.atomic.AtomicLong;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class GreetingController {

    private static final String template = "Hello, %s!";
    private final AtomicLong counter = new AtomicLong();

    @GetMapping("/greeting")
    public Greeting greeting(@RequestParam(value = "name", defaultValue = "World") String name) {
        return new Greeting(counter.incrementAndGet(), String.format(template, name));
    }
}

build.gradle

plugins {
    id 'java'
    id 'org.springframework.boot' version '3.0.1'
    id 'io.spring.dependency-management' version '1.1.0'
}

group = 'com.example'
version = '0.0.1-SNAPSHOT'
sourceCompatibility = '17'

repositories {
    mavenCentral()
}

dependencies {
    implementation 'org.springframework.boot:spring-boot-starter-data-rest'
    implementation 'org.springframework.boot:spring-boot-starter-web'
    implementation 'org.springframework.boot:spring-boot-starter-web-services'
    implementation 'org.springframework.boot:spring-boot-starter-webflux'
    implementation 'org.springframework.session:spring-session-core'
    developmentOnly 'org.springframework.boot:spring-boot-devtools'
    testImplementation 'org.springframework.boot:spring-boot-starter-test'
    testImplementation 'io.projectreactor:reactor-test'
}

tasks.named('test') {
    useJUnitPlatform()
}

排查原因 #

1. 缺失Spring Boot启动类：Spring Boot需要一个标注@SpringBootApplication的启动类来扫描包内的组件（如@RestController标记的控制器）。你的项目中没有这个类，导致Spring无法发现GreetingController，无法注册/greeting路由。
2. 依赖冲突：同时引入了spring-boot-starter-web（Servlet栈）和spring-boot-starter-webflux（Reactor栈），两种Web栈的自动配置会相互干扰，导致路由无法正常初始化。

解决方法 #

1. 添加Spring Boot启动类 #

在com.example.restservice包下创建RestServiceApplication.java：

package com.example.restservice;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class RestServiceApplication {
    public static void main(String[] args) {
        SpringApplication.run(RestServiceApplication.class, args);
    }
}

@SpringBootApplication包含@ComponentScan注解，会自动扫描当前包及子包下的所有Spring组件，让Spring发现并注册GreetingController的路由。

2. 清理冲突依赖 #

修改build.gradle的依赖块，只保留官方示例需要的依赖，移除冲突和不必要的依赖：

dependencies {
    implementation 'org.springframework.boot:spring-boot-starter-web'
    developmentOnly 'org.springframework.boot:spring-boot-devtools'
    testImplementation 'org.springframework.boot:spring-boot-starter-test'
}

删除spring-boot-starter-data-rest、spring-boot-starter-web-services、spring-boot-starter-webflux、spring-session-core和io.projectreactor:reactor-test，避免自动配置冲突。

3. 重启应用测试 #

重新构建项目并启动Spring Boot应用，再次用Postman发送GET请求到http://localhost:8080/greeting，应返回正常响应：

{"id":1,"content":"Hello, World!"}

内容的提问来源于stack exchange，提问作者programmmm