@Target({ElementType.TYPE, ElementType.METHOD})
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface Conditional {
	/**
	 * contion條件的具體實(shí)現(xiàn)類， 必須實(shí)現(xiàn)Condition接口
	 */
	Class<? extends Condition>[] value();
}

@Log4j2
public class CustomerMatchCondition implements Condition {
    @Override
    public boolean matches(ConditionContext context, AnnotatedTypeMetadata metadata) {
        log.info("Process in CustomerMatchCondition.matches method. ");
        return false;
    }
}

@Configuration
@Conditional(CustomerMatchCondition.class)
@Log4j2
public class CusomterConditional {
    public Object newObj() {
        log.info("Process in CusomterConditional.newObj method.");
        return new Object();
    }
}

public abstract class SpringBootCondition implements Condition {
	private final Log logger = LogFactory.getLog(getClass());
	@Override
	public final boolean matches(ConditionContext context, AnnotatedTypeMetadata metadata) {
        // 根據(jù)注解信息， 獲取類或方法名稱
		String classOrMethodName = getClassOrMethodName(metadata);
		try {
            // 獲取實(shí)現(xiàn)類的處理匹配結(jié)果
			ConditionOutcome outcome = getMatchOutcome(context, metadata);
            // 日志打印匹配結(jié)果
			logOutcome(classOrMethodName, outcome);
            // ConditionEvaluationReport中記錄處理結(jié)果信息
			recordEvaluation(context, classOrMethodName, outcome);
			return outcome.isMatch();
		}
		catch (NoClassDefFoundError ex) {
			throw new IllegalStateException("Could not evaluate condition on " + classOrMethodName + " due to "
					+ ex.getMessage() + " not " + "found. Make sure your own configuration does not rely on "
					+ "that class. This can also happen if you are "
					+ "@ComponentScanning a springframework package (e.g. if you "
					+ "put a @ComponentScan in the default package by mistake)", ex);
		}
		catch (RuntimeException ex) {
			throw new IllegalStateException("Error processing condition on " + getName(metadata), ex);
		}
	}
    ...
}

@Target({ ElementType.TYPE, ElementType.METHOD })
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Conditional(OnBeanCondition.class)
public @interface ConditionalOnBean {
    ...
}

@Order(Ordered.LOWEST_PRECEDENCE)
class OnBeanCondition extends FilteringSpringBootCondition implements ConfigurationCondition {
	/**
	 * Bean definition attribute name for factory beans to signal their product type (if
	 * known and it can't be deduced from the factory bean class).
	 */
	public static final String FACTORY_BEAN_OBJECT_TYPE = BeanTypeRegistry.FACTORY_BEAN_OBJECT_TYPE;
	@Override
	public ConfigurationPhase getConfigurationPhase() {
		return ConfigurationPhase.REGISTER_BEAN;
	}
   ...
}

@Override
	protected final ConditionOutcome[] getOutcomes(String[] autoConfigurationClasses,
			AutoConfigurationMetadata autoConfigurationMetadata) {
		// 創(chuàng)建數(shù)組， 記錄自動(dòng)化配置的類信息
        ConditionOutcome[] outcomes = new ConditionOutcome[autoConfigurationClasses.length];
        // 遍歷處理
		for (int i = 0; i < outcomes.length; i++) {
			String autoConfigurationClass = autoConfigurationClasses[i];
			if (autoConfigurationClass != null) {
                // 獲取具有ConditionalOnBean注解設(shè)置的Bean
				Set<String> onBeanTypes = autoConfigurationMetadata.getSet(autoConfigurationClass, "ConditionalOnBean");
                // 記錄outcomes， 條件配置信息
				outcomes[i] = getOutcome(onBeanTypes, ConditionalOnBean.class);
				if (outcomes[i] == null) {
                    // 為空， 則降級(jí)獲取ConditionalOnSingleCandidate配置信息
					Set<String> onSingleCandidateTypes = autoConfigurationMetadata.getSet(autoConfigurationClass,
							"ConditionalOnSingleCandidate");
					outcomes[i] = getOutcome(onSingleCandidateTypes, ConditionalOnSingleCandidate.class);
				}
			}
		}
		return outcomes;
	}

@Override
	public ConditionOutcome getMatchOutcome(ConditionContext context, AnnotatedTypeMetadata metadata) {
		ConditionMessage matchMessage = ConditionMessage.empty();
        // 判斷注解類型， ConditionalOnBean處理邏輯
		if (metadata.isAnnotated(ConditionalOnBean.class.getName())) {
			BeanSearchSpec spec = new BeanSearchSpec(context, metadata, ConditionalOnBean.class);
			MatchResult matchResult = getMatchingBeans(context, spec);
			if (!matchResult.isAllMatched()) {
				String reason = createOnBeanNoMatchReason(matchResult);
				return ConditionOutcome						.noMatch(ConditionMessage.forCondition(ConditionalOnBean.class, spec).because(reason));
			}
			matchMessage = matchMessage.andCondition(ConditionalOnBean.class, spec).found("bean", "beans")
					.items(Style.QUOTE, matchResult.getNamesOfAllMatches());
		}
        // ConditionalOnSingleCandidate注解處理邏輯
		if (metadata.isAnnotated(ConditionalOnSingleCandidate.class.getName())) {
			BeanSearchSpec spec = new SingleCandidateBeanSearchSpec(context, metadata,
					ConditionalOnSingleCandidate.class);
			MatchResult matchResult = getMatchingBeans(context, spec);
			if (!matchResult.isAllMatched()) {
				return ConditionOutcome.noMatch(ConditionMessage.forCondition(ConditionalOnSingleCandidate.class, spec)
						.didNotFind("any beans").atAll());
			}
			else if (!hasSingleAutowireCandidate(context.getBeanFactory(), matchResult.getNamesOfAllMatches(),
					spec.getStrategy() == SearchStrategy.ALL)) {
				return ConditionOutcome.noMatch(ConditionMessage.forCondition(ConditionalOnSingleCandidate.class, spec)
						.didNotFind("a primary bean from beans")
						.items(Style.QUOTE, matchResult.getNamesOfAllMatches()));
			}
			matchMessage = matchMessage.andCondition(ConditionalOnSingleCandidate.class, spec)
					.found("a primary bean from beans").items(Style.QUOTE, matchResult.getNamesOfAllMatches());
		}
        // ConditionalOnMissingBean注解處理邏輯
		if (metadata.isAnnotated(ConditionalOnMissingBean.class.getName())) {
			BeanSearchSpec spec = new BeanSearchSpec(context, metadata, ConditionalOnMissingBean.class);
			MatchResult matchResult = getMatchingBeans(context, spec);
			if (matchResult.isAnyMatched()) {
				String reason = createOnMissingBeanNoMatchReason(matchResult);
				return ConditionOutcome
						.noMatch(ConditionMessage.forCondition(ConditionalOnMissingBean.class, spec).because(reason));
			}
			matchMessage = matchMessage.andCondition(ConditionalOnMissingBean.class, spec).didNotFind("any beans")
					.atAll();
		}
		return ConditionOutcome.match(matchMessage);
	}

protected final MatchResult getMatchingBeans(ConditionContext context, BeanSearchSpec beans) {
		ConfigurableListableBeanFactory beanFactory = context.getBeanFactory();
        // 判斷bean的搜尋策略， ANCESTORS為搜索所有父容器的上下文定義
		if (beans.getStrategy() == SearchStrategy.ANCESTORS) {
			BeanFactory parent = beanFactory.getParentBeanFactory();
			Assert.isInstanceOf(ConfigurableListableBeanFactory.class, parent, "Unable to use SearchStrategy.PARENTS");
            // 父容器轉(zhuǎn)換
			beanFactory = (ConfigurableListableBeanFactory) parent;
		}
		MatchResult matchResult = new MatchResult();
        // 判斷bean的搜尋策略， 是否為CURRENT當(dāng)前上下文
		boolean considerHierarchy = beans.getStrategy() != SearchStrategy.CURRENT;
		TypeExtractor typeExtractor = beans.getTypeExtractor(context.getClassLoader());
		List<String> beansIgnoredByType = getNamesOfBeansIgnoredByType(beans.getIgnoredTypes(), typeExtractor,
				beanFactory, context, considerHierarchy);
        // 根據(jù)bean的類型遍歷判斷是否符合規(guī)則
		for (String type : beans.getTypes()) {
            // type類型的具體處理邏輯， 內(nèi)部為嵌套調(diào)用
			Collection<String> typeMatches = getBeanNamesForType(beanFactory, type, typeExtractor,
					context.getClassLoader(), considerHierarchy);
			typeMatches.removeAll(beansIgnoredByType);
			if (typeMatches.isEmpty()) {
				matchResult.recordUnmatchedType(type);
			}
			else {
				matchResult.recordMatchedType(type, typeMatches);
			}
		}
        // 根據(jù)bean的注解遍歷判斷是否符合規(guī)則
		for (String annotation : beans.getAnnotations()) {
			List<String> annotationMatches = Arrays.asList(
                    // Annotation類型的具體處理邏輯， 內(nèi)部為嵌套調(diào)用
					getBeanNamesForAnnotation(beanFactory, annotation, context.getClassLoader(), considerHierarchy));
			annotationMatches.removeAll(beansIgnoredByType);
			if (annotationMatches.isEmpty()) {
				matchResult.recordUnmatchedAnnotation(annotation);
			}
			else {
				matchResult.recordMatchedAnnotation(annotation, annotationMatches);
			}
		}
        // 根據(jù)bean的名稱遍歷判斷是否符合規(guī)則
		for (String beanName : beans.getNames()) {
			if (!beansIgnoredByType.contains(beanName) && containsBean(beanFactory, beanName, considerHierarchy)) {
				matchResult.recordMatchedName(beanName);
			}
			else {
				matchResult.recordUnmatchedName(beanName);
			}
		}
		return matchResult;
	}