@Conditional注解的使用

条件判断注解Conditional

SpringBoot底层大量使用的注解

1. 注解的定义

由此可知需要实现condition接口
@Target({ElementType.TYPE, ElementType.METHOD})
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface Conditional {

	/**
	 * All {@link Condition} classes that must {@linkplain Condition#matches match}
	 * in order for the component to be registered.
	 */
	Class<? extends Condition>[] value();

}

2.使用步骤-->实现Condition接口

public class MyWindowsCondition implements Condition {
    /**
     * ConditionContext:判断条件能使用的上下文环境
     * AnnotatedTypeMetadata:注释信息
     *
     * @param context
     * @param metadata
     * @return
     */
    @Override
    public boolean matches(ConditionContext context, AnnotatedTypeMetadata metadata) {
        //1.获取IOC容器
        BeanFactory beanFactory = context.getBeanFactory();
        //2.获取类加载器
        ClassLoader classLoader = context.getClassLoader();
        //3.获取当前环境信息
        Environment environment = context.getEnvironment();
        //4.bean的注册
        BeanDefinitionRegistry registry = context.getRegistry();
        if (environment.getProperty("os.name").equals("Windows 10")) {
            return true;
        }
        return false;
    }
}

3.引入方式

    @Bean
    @Conditional({MyWindowsCondition.class})
    public Dog dog3() {
        return new Dog(1, "condition-->Dog-->windows");
    }

4.当条件满足的时候就会将组件注入容器中