一. 命名規範

springboot提供的starter都是以spring-boot-starter-xxx的方式命名的，針對自定義的starter，官方建議以xxx-spring-boot-starter命名予以區分。見官方說明

二. 依賴

	<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>
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可以將其他的必要的依賴加入進來。

三. 寫法

1. META-INF

在resources下新建包META-INF,並新增檔案spring.factories。內容如下：

org.springframework.boot.autoconfigure.EnableAutoConfiguration=xxx.HelloStarterEnableAutoConfiguration
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其中xxx為自動配置的核心類。寫法是固定的，springboot會掃描該檔案作為配置類。

2.核心註解

@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());
       }
   
   }
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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;
       }
   }
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   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);
          }
      
      }
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解釋：當專案依賴該starter，並且配置檔案中包含hello.service為字首且hello.service.enable為true時，就會自動生成HelloService的bean。

附上程式碼庫 hello-spring-boot-starter