自定义一个注解，继承 @Conditional 注解
// 派生注解
@Retention(RetentionPolicy.RUNTIME)
@Target({ ElementType.TYPE, ElementType.METHOD })
@Documented
@Conditional(CustomConditional.class)
public @interface ConditionalOnCustom {
String[] value() default {};
}注解的处理类
public class CustomConditional implements Condition {
@Override
public boolean matches(ConditionContext context, AnnotatedTypeMetadata metadata) {
// 获取到自定义注解中的 value 值
String[] properties = (String[]) metadata.getAnnotationAttributes("smoketest.test.condition.ConditionalOnCustom").get("value");
// 遍历自定义属性的 value 值
for (String property : properties) {
// 获取定义在配置文件中的值，并且 equals("customBean") 则返回 true
if ("customBean".equals(context.getEnvironment().getProperty(property))) {
return true;
}
}
return false;
}
}
使用注解
@Component
@ConditionalOnCustom({"smoketest.test.condition.bean"})
public class ConditionalUse {
}application.properties 中配置变量
smoketest.test.condition.bean = customBean
获取 ConditionalUse 对象
@SpringBootApplication
@ConfigurationPropertiesScan
public class SampleTestApplication {
public static void main(String[] args) {
ConfigurableApplicationContext context = SpringApplication.run(SampleTestApplication.class, args);
ConditionalUse bean = context.getBean(ConditionalUse.class);
System.out.println(bean);
}
}
程序启动可以看到成功获取 ConditionalUse 对象
@Conditional 注解在 spring 的 ConfigurationClassParse 类中会调用 ConditionEvaluator.shouldSkip() 方法进行判断，Condition 接口的 matches() 是否返回 true，如果返回 true，就实例化对象，并注册到 spring 容器中
if ((requiredPhase == null || requiredPhase == phase) && !condition.matches(this.context, metadata)) { return true; }
