一. 命名规范

springboot提供的starter都是以spring-boot-starter-xxx的方式命名的，针对自定义的starter，官方建议以xxx-spring-boot-starter命名予以区分。见官方说明

二. 依赖

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-autoconfigure</artifactId>
        </dependency>
    </dependencies>
    <dependencyManagement>
        <dependencies>
            <dependency>
                <!-- Import dependency management from Spring Boot -->
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-dependencies</artifactId>
                <version>2.1.0.RELEASE</version>
                <type>pom</type>
                <scope>import</scope>
            </dependency>
        </dependencies>
    </dependencyManagement>

可以将其他的必要的依赖加入进来。

三. 写法

1. META-INF

在resources下新建包META-INF,并新增文件spring.factories。内容如下：

org.springframework.boot.autoconfigure.EnableAutoConfiguration=xxx.HelloStarterEnableAutoConfiguration

其中xxx为自动配置的核心类。写法是固定的，springboot会扫描该文件作为配置类。

2.核心注解

@Configuation

@EnableConfiguationProerties

@ConditionalOnProperties

1. HelloStarterEnableAutoConfiguration

   @Configuration
   @ConditionalOnClass(HelloService.class)
   @EnableConfigurationProperties(HelloServiceProperties.class)
   public class HelloStarterEnableAutoConfiguration {
   
       private final HelloServiceProperties helloServiceProperties;
   
       @Autowired
       public HelloStarterEnableAutoConfiguration(HelloServiceProperties helloServiceProperties) {
           this.helloServiceProperties = helloServiceProperties;
       }
   
       @Bean
       @ConditionalOnProperty(prefix = "hello.service", name = "enable", havingValue = "true")
       HelloService helloService() {
           return new HelloService(helloServiceProperties.getPrefix(), helloServiceProperties.getSuffix());
       }
   
   }
   

2. HelloServiceProperties

   @ConfigurationProperties("hello.service")
   public class HelloServiceProperties {
   
       private String prefix;
   
       private String suffix;
   
       public String getPrefix() {
           return prefix;
       }
   
       public void setPrefix(String prefix) {
           this.prefix = prefix;
       }
   
       public String getSuffix() {
           return suffix;
       }
   
       public void setSuffix(String suffix) {
           this.suffix = suffix;
       }
   }
   

   3. HelloService

      public class HelloService {
      
          private String prefix;
      
          private String suffix;
      
          public HelloService(String prefix, String suffix) {
              this.prefix = prefix;
              this.suffix = suffix;
          }
      
          public String say(String text) {
              return String.format("%s , hi , %s , %s", prefix, text, suffix);
          }
      
      }
      

解释：当项目依赖该starter，并且配置文件中包含hello.service为前缀且hello.service.enable为true时，就会自动生成HelloService的bean。

附上代码库 hello-spring-boot-starter