Spring Boot启动扫描无法识别Reactive Repository的问题排查

背景 #

我有一个Spring Boot沙箱应用，打算采用响应式开发方案，使用PostgreSQL作为数据库，已经引入R2DBC实现响应式Repository，但应用启动时提示找不到Repository的Bean。

相关代码 #

主应用类 #

@SpringBootApplication
public class Springboot2Application {
    public static void main(String[] args) {
        SpringApplication.run(Springboot2Application.class, args);
    }
}

Repository接口 #

@Repository
public interface ToDoRepository extends ReactiveCrudRepository<ToDo,String> {
}

Controller类 #

@RestController
@RequestMapping("/api/v1")
public class ToDoController {
    private final ToDoRepository repository;
    
    public ToDoController(ToDoRepository repository) {
        this.repository = repository;
    }

    @GetMapping(value = "/to-do", produces = {
            MediaType.APPLICATION_JSON_VALUE, 
            MediaType.APPLICATION_XML_VALUE, 
            MediaType.TEXT_XML_VALUE})
    public ResponseEntity<Flux<ToDo>> getToDos(@RequestHeader HttpHeaders headers){
        return ResponseEntity.ok().body(repository.findAll());
    }
}

实体类 #

@Data
@RequiredArgsConstructor
@Entity
@Table(name = "todo")
public class ToDo {
    @Id
    @NotNull
    @GeneratedValue(generator = "system-uuid")
    @GenericGenerator(name = "system-uuid", strategy = "uuid")
    private String id;
    @NotNull
    @NotBlank
    private String description;
    @CreationTimestamp
    private Timestamp created;
    @UpdateTimestamp
    private Timestamp modified;
    private boolean completed;
}

R2DBC配置类 #

@Configuration
@EnableR2dbcRepositories(basePackages = "com.springboot2.repository")
public class R2DBCConfig extends AbstractR2dbcConfiguration {
    @Bean
    public ConnectionFactory connectionFactory() {
        return ConnectionFactories.get(
                ConnectionFactoryOptions.builder()
                        .option(DRIVER, "postgresql")
                        .option(HOST, "localhost")
                        .option(PORT, 5432)
                        .option(USER, "admin")
                        .option(PASSWORD, "admin")
                        .option(DATABASE, "springdb")
                        .build());
    }
}

启动错误信息 #

描述：
Parameter 0 of constructor in com.springboot2.controller.ToDoController required a bean of type 'com.springboot2.repository.ToDoRepository' that could not be found.

Action:
Consider defining a bean of type 'com.springboot2.repository.ToDoRepository' in your configuration.

已尝试的解决方法 #

• 添加@ComponentScan注解
• 将ToDoRepository移至Springboot2Application所在的根包下
  但问题依然存在。

pom.xml文件内容 #

<?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>2.7.3</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <groupId>com.springboot</groupId>
    <artifactId>springboot</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>springboot2</name>
    <description>Demo project for Spring Boot</description>
    <properties>
        <java.version>8</java.version>
        <spring-cloud.version>2021.0.3</spring-cloud.version>
<!--        <spring-shell.version>2.1.0</spring-shell.version>-->
    </properties>
    <dependencies>
        <!--        DB,ORM, and plugins-->
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-actuator</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-data-jpa</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-data-r2dbc</artifactId>
        </dependency>
        <dependency>
            <groupId>io.r2dbc</groupId>
            <artifactId>r2dbc-postgresql</artifactId>
            <version>0.8.1.RELEASE</version>
        </dependency>
        <dependency>
            <groupId>org.postgresql</groupId>
            <artifactId>postgresql</artifactId>
            <scope>runtime</scope>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-webflux</artifactId>
        </dependency>
        <!--        Reactive libs-->
        <dependency>
            <groupId>io.projectreactor</groupId>
            <artifactId>reactor-test</artifactId>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-validation</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-devtools</artifactId>
            <scope>runtime</scope>
            <optional>true</optional>
        </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>
    </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>

问题原因及解决方案 #

1. 包路径不匹配 #

@EnableR2dbcRepositories注解指定的包是com.springboot2.repository，但pom.xml的groupId是com.springboot，实际包结构大概率是com.springboot.repository。检查Repository所在包路径，确保和注解配置一致：

@EnableR2dbcRepositories(basePackages = "com.springboot.repository")

2. JPA与R2DBC依赖冲突 #

pom.xml同时引入了spring-boot-starter-data-jpa和spring-boot-starter-data-r2dbc，两者的Repository扫描逻辑会互相干扰。移除JPA依赖，因为响应式开发不需要JPA：

<!-- 删除该依赖 -->
<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-data-jpa</artifactId>
</dependency>

3. 实体类注解错误 #

R2DBC不支持JPA的@Entity注解，且不兼容@GeneratedValue的UUID生成方式。修改实体类：

@Data
@NoArgsConstructor // 添加无参构造，R2DBC需要
@Table(name = "todo")
public class ToDo {
    @Id
    @NotNull
    private String id;
    @NotNull
    @NotBlank
    private String description;
    private Timestamp created;
    private Timestamp modified;
    private boolean completed;

    // 手动生成UUID
    public ToDo(String description) {
        this.id = UUID.randomUUID().toString();
        this.description = description;
        this.created = new Timestamp(System.currentTimeMillis());
        this.modified = this.created;
    }
}

4. 简化R2DBC配置 #

删除自定义的R2DBCConfig类，改用配置文件配置连接信息，在主应用类上添加@EnableR2dbcRepositories：

@SpringBootApplication
@EnableR2dbcRepositories(basePackages = "com.springboot.repository")
public class Springboot2Application {
    public static void main(String[] args) {
        SpringApplication.run(Springboot2Application.class, args);
    }
}

application.properties配置：

spring.r2dbc.url=r2dbc:postgresql://localhost:5432/springdb
spring.r2dbc.username=admin
spring.r2dbc.password=admin

内容的提问来源于stack exchange，提问作者Sam Fisher