Conditional study notes for Springboot conditional assembly

1. Write the Condition implementation class (refer to: OnPropertyCondition)

   public class OnSystemPropertyCondition  implements Condition {
         
         
       @Override
       public boolean matches(ConditionContext context, AnnotatedTypeMetadata metadata) {
         
         
           Map<String, Object> attributes =
                   metadata.getAnnotationAttributes(ConditionalOnSystemProperty.class.getName());
           String propertyName = (String) attributes.get("name") ;
           String propertyValue = (String) attributes.get("value") ;
           String systemPropertyValue = System.getProperty(propertyName) ;
           return propertyValue.equalsIgnoreCase(systemPropertyValue);
       }
   }
   

2. Write Conditional annotation classes (refer to: ConditionalOnProperty)

   @Documented
   @Retention(RetentionPolicy.RUNTIME)
   @Target({
         
          ElementType.TYPE, ElementType.METHOD })
   @Conditional(OnSystemPropertyCondition.class)
   public @interface ConditionalOnSystemProperty{
         
         
       // Java 系统属性名称
       String name() default "" ;
       // Java 系统属性值
       String value() default "" ;
   }
   

3. Business and startup class writing

   @Slf4j
   public class ConditionalOnSystemPropertyApplication {
         
         
       @Bean
       @ConditionalOnSystemProperty(name = "user.name", value = "yichengjie")
       public String helloWorld(){
         
         
           return "Hello, yicj" ;
       }
       public static void main(String[] args) {
         
         
           ConfigurableApplicationContext ctx = new SpringApplicationBuilder(ConditionalOnSystemPropertyApplication.class)
                   .web(WebApplicationType.NONE)
                   .run(args);
           String bean = ctx.getBean("helloWorld", String.class);
           log.info("====> bean : {}", bean);
           ctx.close();
       }
   }