@Configuration
@ConditionalOnProperty(
        name = "coverage.aws.topic"
)
public class CoverageSQSConfig {
    @Value("${coverage.aws.region}")
    private String awsRegion;
    @Value("${coverage.aws.access.key}")
    private String accessKey;
    @Value("${coverage.aws.secret.key}")
    private String secretKey;
    @Bean(name = "coverageSQSListenerFactory")
    public DefaultJmsListenerContainerFactory sqsListenerContainerFactory(){
        return getDefaultJmsListenerContainerFactory(awsRegion, accessKey, secretKey);
    }
    private DefaultJmsListenerContainerFactory getDefaultJmsListenerContainerFactory(String awsRegion, String accessKey, String secretKey) {
        DefaultJmsListenerContainerFactory sqsFactory = new DefaultJmsListenerContainerFactory();
        sqsFactory.setConnectionFactory(new SQSConnectionFactory(
                new ProviderConfiguration(),
                AmazonSQSClientBuilder.standard()
                        .withRegion(Region.of(awsRegion).id())
                        .withCredentials(new AWSStaticCredentialsProvider(new BasicAWSCredentials(accessKey, secretKey)))
                        .build()));
        sqsFactory.setConcurrency("3-10");
        sqsFactory.setReceiveTimeout(10*1000L);
        sqsFactory.setRecoveryInterval(1000L);
        return sqsFactory;
    }
}

package org.springframework.boot.autoconfigure.condition;
...
@Order(Ordered.HIGHEST_PRECEDENCE + 40)
class OnPropertyCondition extends SpringBootCondition {
  @Override
  public ConditionOutcome getMatchOutcome(ConditionContext context, AnnotatedTypeMetadata metadata) {
    // 通過(guò)獲類(lèi)原始數(shù)據(jù)上的ConditionalOnProperty注解的參數(shù)值
    List<AnnotationAttributes> allAnnotationAttributes = annotationAttributesFromMultiValueMap(
        metadata.getAllAnnotationAttributes(ConditionalOnProperty.class.getName()));
    List<ConditionMessage> noMatch = new ArrayList<>();
    List<ConditionMessage> match = new ArrayList<>();
    for (AnnotationAttributes annotationAttributes : allAnnotationAttributes) {
     // 通過(guò)屬性值，逐一判斷配置信息中的信息是否滿(mǎn)足 ， context.getEnvironment() 能獲取到所有的配置信息
      ConditionOutcome outcome = determineOutcome(annotationAttributes, context.getEnvironment());
      (outcome.isMatch() ? match : noMatch).add(outcome.getConditionMessage());
    }
    if (!noMatch.isEmpty()) {
      return ConditionOutcome.noMatch(ConditionMessage.of(noMatch));
    }
    return ConditionOutcome.match(ConditionMessage.of(match));
  }
  private List<AnnotationAttributes> annotationAttributesFromMultiValueMap(
      MultiValueMap<String, Object> multiValueMap) {
    ...
    return annotationAttributes;
  }
  private ConditionOutcome determineOutcome(AnnotationAttributes annotationAttributes, PropertyResolver resolver) {
    Spec spec = new Spec(annotationAttributes);
    List<String> missingProperties = new ArrayList<>();
    List<String> nonMatchingProperties = new ArrayList<>();
    // 通過(guò)屬性值，判斷配置信息中的信息是否滿(mǎn)足
    spec.collectProperties(resolver, missingProperties, nonMatchingProperties);
    if (!missingProperties.isEmpty()) {
      return ConditionOutcome.noMatch(ConditionMessage.forCondition(ConditionalOnProperty.class, spec)
          .didNotFind("property", "properties").items(Style.QUOTE, missingProperties));
    }
    if (!nonMatchingProperties.isEmpty()) {
      return ConditionOutcome.noMatch(ConditionMessage.forCondition(ConditionalOnProperty.class, spec)
          .found("different value in property", "different value in properties")
          .items(Style.QUOTE, nonMatchingProperties));
    }
    return ConditionOutcome
        .match(ConditionMessage.forCondition(ConditionalOnProperty.class, spec).because("matched"));
  }
  private static class Spec {
    private final String prefix;
    private final String havingValue;
    private final String[] names;
    private final boolean matchIfMissing;
    Spec(AnnotationAttributes annotationAttributes) {
      ...
    }
    private String[] getNames(Map<String, Object> annotationAttributes) {
      ...
    }
    private void collectProperties(PropertyResolver resolver, List<String> missing, List<String> nonMatching) {
      for (String name : this.names) {
        String key = this.prefix + name;
        if (resolver.containsProperty(key)) {
        // havingValue 默認(rèn)為 "" 
          if (!isMatch(resolver.getProperty(key), this.havingValue)) {
            nonMatching.add(name);
          }
        }
        else {
          if (!this.matchIfMissing) {
            missing.add(name);
          }
        }
      }
    }
    private boolean isMatch(String value, String requiredValue) {
      if (StringUtils.hasLength(requiredValue)) {
        return requiredValue.equalsIgnoreCase(value);
      }
      // havingValue 默認(rèn)為 "" ，因此只要對(duì)應(yīng)的屬性不為false，在注解中沒(méi)填havingValue的情況下，都是會(huì)match上conditon，即都會(huì)被加載
      return !"false".equalsIgnoreCase(value);
    }
    @Override
    public String toString() {
      ...
    }
  }
}

// org.springframework.context.annotation.ClassPathScanningCandidateComponentProvider
  /**
   * Determine whether the given class does not match any exclude filter
   * and does match at least one include filter.
   * @param metadataReader the ASM ClassReader for the class
   * @return whether the class qualifies as a candidate component
   */
  protected boolean isCandidateComponent(MetadataReader metadataReader) throws IOException {
    for (TypeFilter tf : this.excludeFilters) {
      if (tf.match(metadataReader, getMetadataReaderFactory())) {
        return false;
      }
    }
    for (TypeFilter tf : this.includeFilters) {
      if (tf.match(metadataReader, getMetadataReaderFactory())) {
        // conditons 相關(guān)的入口，
        return isConditionMatch(metadataReader);
      }
    }
    return false;
  }

    @Value("${coverage.aws.region}")
    private String awsRegion;
    @Value("${coverage.aws.access.key}")
    private String accessKey;
    @Value("${coverage.aws.secret.key}")
    private String secretKey;
    @Bean(name = "coverageSQSListenerFactory")
    public DefaultJmsListenerContainerFactory sqsListenerContainerFactory(){
        return getDefaultJmsListenerContainerFactory(awsRegion, accessKey, secretKey);
    }