Spring Boot REST API返回404 Not Found问题排查求助

问题描述 #

我是Spring Boot新手，尝试开发一个简单的REST API服务，编写了一个返回字符串的接口，但在Postman中始终收到404 Not Found响应。我确认请求URL正确且已在类上添加@RestController注解，虽知晓当前接口实现不规范，但仅为测试用途，不知为何出现404问题。项目结构为：src/main/java/com/example/demo下包含启动类DemoApplication.java，同级目录下有controller文件夹，PhotoController.java位于该文件夹中。

控制器代码 #

@RestController
public class PhotoController {
    @GetMapping(path = "/api/photos", produces = "application/json")
    public String getAll(){
        return "finito";
    }
}

pom.xml 配置 #

<?xml version="1.0" encoding="UTF-8"?>
<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 https://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>3.1.0</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <groupId>com.example</groupId>
    <artifactId>demo</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>demo</name>
    <description>Demo project for Spring Boot</description>
    <properties>
        <java.version>17</java.version>
    </properties>
    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-data-jpa</artifactId>
        </dependency>
        <dependency>
            <groupId>com.mysql</groupId>
            <artifactId>mysql-connector-j</artifactId>
            <version>8.0.33</version>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>

        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <optional>true</optional>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>jakarta.persistence</groupId>
            <artifactId>jakarta.persistence-api</artifactId>
            <version>3.1.0</version>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
                <configuration>
                    <excludes>
                        <exclude>
                            <groupId>org.projectlombok</groupId>
                            <artifactId>lombok</artifactId>
                        </exclude>
                    </excludes>
                </configuration>
            </plugin>
        </plugins>
    </build>

</project>

application.properties 配置 #

debug = true
spring.jpa.hibernate.ddl-auto=update
spring.datasource.url=jdbc:mysql://localhost:3306/photos
spring.datasource.username=root
spring.datasource.password=
spring.datasource.driver-class-name=com.mysql.cj.jdbc.Driver
spring.jpa.show-sql: true
spring.jpa.properties.javax.persistence.schema-generation.scripts.action=drop-and-create
spring.jpa.properties.javax.persistence.schema-generation.scripts.create-target=create.sql
spring.jpa.properties.javax.persistence.schema-generation.scripts.drop-target=drop.sql
spring.jpa.properties.hibernate.format.sql=true

排查方向 #

1. 启动类扫描范围：Spring Boot默认扫描启动类所在包及其子包。如果启动类DemoApplication在com.example.demo包，控制器在com.example.demo.controller属于子包，扫描逻辑正常；若控制器在其他路径，需在启动类添加@ComponentScan(basePackages = "控制器所在包全路径")指定扫描范围。
2. 请求URL匹配：确认Postman请求为GET http://localhost:8080/api/photos（默认端口8080），注意路径大小写、是否有多余斜杠；若配置了server.servlet.context-path，需在URL前加上该前缀。
3. 组件初始化日志：查看启动日志，若存在Mapping GET "/api/photos" to public java.lang.String com.example.demo.controller.PhotoController.getAll()这类日志，说明控制器已被加载；无此日志则表示控制器未被扫描到。
4. 依赖完整性：确认spring-boot-starter-web依赖已正确引入，该依赖是Spring MVC运行的基础，可检查Maven依赖是否下载完整。

内容的提问来源于stack exchange，提问作者user21357629