Spring的@Conditional详解

@Component
public class TestConfig {
    @Bean
    // 注入Bean之前增加限制条件：MyCondition，条件满足才会构造TestBean同时注入
    @Conditional(MyCondition.class)
    public TestBean testbean() {
        System.out.println("=====run new TestBean");
        TestBean testBean = new TestBean();
        testBean.setId(1L);
        return testBean;
    }
}
public class TestBean {
    private Long id;
    public Long getId() {
        return id;
    }
    public void setId(Long id) {
        this.id = id;
    }
    @Override
    public String toString() {
        return "TestBean{" +
                "id=" + id +
                '}';
    }
}

public class MyCondition implements Condition {
    @Override
    public boolean matches(ConditionContext context, AnnotatedTypeMetadata metadata) {
        //context能够获取到IOC相关的信息、对象
        //获取ioc使用的beanFactory
        ConfigurableListableBeanFactory beanFactory = context.getBeanFactory();
        //获取类加载器
        ClassLoader classLoader = context.getClassLoader();
        //获取当前环境信息
        Environment environment = context.getEnvironment();
        //获取bean定义的注册类
        BeanDefinitionRegistry registry = context.getRegistry();
        //metadata能取到注解的元信息
        metadata.getAnnotations().forEach(a -> {
            //注解的class
            Class<Annotation> type = a.getType();
            //注解对应的attribute
            Object value = a.getValue("value").get();
        });
        //返回false表示未满足条件，不进行构造和注入；返回true表示满足条件，正常构造和注入
        return false;
    }
}

@SpringBootTest
class MyConsul1ApplicationTests {
	//required=false：表示如果testBean在容器中不存在，也不会异常中断，而是单纯的testBean=null而已
	@Autowired(required=false)
	private TestBean testBean;
	@Test
	public void test() {
		System.out.println("testBean = " + testBean);
	}
}

public boolean shouldSkip(@Nullable AnnotatedTypeMetadata metadata, @Nullable ConfigurationPhase phase) {
		if (metadata == null || !metadata.isAnnotated(Conditional.class.getName())) {
			return false;
		}
//判断是：PARSE_CONFIGURATION还是REGISTER_BEAN
//PARSE_CONFIGURATION：代表解析配置类阶段，也就是将配置类转换为ConfigurationClass阶段
//REGISTER_BEAN：代表配置类注册为bean阶段，也就是将配置类是否需要在将其注册到IOC容器阶段
		if (phase == null) {
			if (metadata instanceof AnnotationMetadata &&
					ConfigurationClassUtils.isConfigurationCandidate((AnnotationMetadata) metadata)) {
				return shouldSkip(metadata, ConfigurationPhase.PARSE_CONFIGURATION);
			}
			return shouldSkip(metadata, ConfigurationPhase.REGISTER_BEAN);
		}
		List<Condition> conditions = new ArrayList<>();
		for (String[] conditionClasses : getConditionClasses(metadata)) {
			for (String conditionClass : conditionClasses) {
				Condition condition = getCondition(conditionClass, this.context.getClassLoader());
				conditions.add(condition);
			}
		}
		AnnotationAwareOrderComparator.sort(conditions);
		for (Condition condition : conditions) {
			ConfigurationPhase requiredPhase = null;
			if (condition instanceof ConfigurationCondition) {
				requiredPhase = ((ConfigurationCondition) condition).getConfigurationPhase();
			}
			//这里进行matches回调，决定是否继续
			if ((requiredPhase == null || requiredPhase == phase) && !condition.matches(this.context, metadata)) {
				return true;
			}
		}
		return false;
	}