如何自定义一个SpringBoot Starter(步骤和代码示例)

my-starter-parent
├── my-spring-boot-autoconfigure  // 自动配置核心
└── my-spring-boot-starter        // 轻量依赖聚合

<dependencies>
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-autoconfigure</artifactId>
        <version>3.1.0</version>
    </dependency>
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-configuration-processor</artifactId>
        <version>3.1.0</version>
        <optional>true</optional>
    </dependency>
</dependencies>

@ConfigurationProperties(prefix = "my.service")
public class MyServiceProperties {
    private String prefix = "Hello";
    private String suffix = "!";
    // 省略 getter/setter
}

public class MyService {
    private final String prefix;
    private final String suffix;
    public MyService(String prefix, String suffix) {
        this.prefix = prefix;
        this.suffix = suffix;
    }
    public String greet(String name) {
        return prefix + " " + name + suffix;
    }
}

@Configuration
@EnableConfigurationProperties(MyServiceProperties.class)
@ConditionalOnClass(MyService.class) // 类路径存在时生效
@ConditionalOnProperty(prefix = "my.service", name = "enabled", matchIfMissing = true)
public class MyServiceAutoConfiguration {
    @Bean
    @ConditionalOnMissingBean // 用户未定义时初始化
    public MyService myService(MyServiceProperties properties) {
        return new MyService(properties.getPrefix(), properties.getSuffix());
    }
}

com.example.autoconfigure.MyServiceAutoConfiguration

<dependencies>
    <dependency>
        <groupId>com.example</groupId>
        <artifactId>my-spring-boot-autoconfigure</artifactId>
        <version>1.0.0</version>
    </dependency>
</dependencies>

mvn clean install

<dependency>
    <groupId>com.example</groupId>
    <artifactId>my-spring-boot-starter</artifactId>
    <version>1.0.0</version>
</dependency>

my:
  service:
    prefix: "Welcome"
    suffix: "!!!"
    # enabled: true # 默认启用

@RestController
public class DemoController {
    @Autowired
    private MyService myService;
    @GetMapping("/greet")
    public String greet(String name) {
        return myService.greet(name);
    }
}

@Bean
@ConditionalOnWebApplication // 仅Web环境生效
@ConditionalOnMissingBean
public MyWebService myWebService() {...}

@Bean
public MyServiceMetrics myServiceMetrics(MyService service) {
    return new MyServiceMetrics(service);
}

{
  "properties": [
    {
      "name": "my.service.prefix",
      "type": "java.lang.String",
      "defaultValue": "Hello",
      "description": "Custom greeting prefix."
    }
  ]
}