记一次解决Nacos-SpringBoot不支持@ConditionalOnProperty

错误介绍

@ConditionalOnProperty配置生效问题

错误缘由分析

在使用Nacos-Config-SpringBoot时，有使用者反馈说没法支持@ConditionalOnProperty注解，通过研究Nacos-Config-SpringBoot、Nacos-Spring-Context源码以及调试跟踪SpringBoot的初始化流程，最终发现问题所在——@ConditionalOnProperty的解析时间与Nacos-Spring-Context相关Bean的注册以及工做时间存在前后问题（其本质缘由就是Bean的加载顺序）

@ConditionalOnProperty解析时间

要想知道@ConditionalOnProperty注解什么时候被Spring解析，首先要看另一个类——ConfigurationClassPostProcessor，这个类实现了BeanFactoryPostProcessor接口，所以他能够在Spring的bean建立以前，对bean进行修改，即Spring容许BeanFactoryPostProcessor在容器实例化任何其余bean以前读取配置元数据，并根据其进行修改，就好比@ConditionalOnProperty注解经常使用来根据配置文件的相关配置控制是否须要建立相应的bean。

核心代码

ConfigurationClassPostProcessor执行、装载时机

refreshContext(context);

@Override
protected final void refreshBeanFactory() throws BeansException {
		...
				loadBeanDefinitions(beanFactory);
				synchronized (this.beanFactoryMonitor) {
						this.beanFactory = beanFactory;
				}
		}
		catch (IOException ex) {
			throw new ApplicationContextException("I/O error parsing bean definition source for " + getDisplayName(), ex);
		}
}
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处理@Configuration等注解的处理代码

public void processConfigBeanDefinitions(BeanDefinitionRegistry registry) {
    List<BeanDefinitionHolder> configCandidates = new ArrayList();
    String[] candidateNames = registry.getBeanDefinitionNames();
    String[] var4 = candidateNames;
    int var5 = candidateNames.length;

    ...

        do {
            parser.parse(candidates);
            parser.validate();
            Set<ConfigurationClass> configClasses = new LinkedHashSet(parser.getConfigurationClasses());
            configClasses.removeAll(alreadyParsed);
            if (this.reader == null) {
                this.reader = new ConfigurationClassBeanDefinitionReader(registry, this.sourceExtractor, this.resourceLoader, this.environment, this.importBeanNameGenerator, parser.getImportRegistry());
            }
            ...
}
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在代码parser.getConfigurationClasses()执行后，会根据Environment中的配置元数据以及@ConditionalOnProperty中的设置，对bean进行过滤操做，不满条件的bean不会被转载进Spring Container中

people.enable=false时

people.enable=true时

（提醒：之因此这里nacos的配置可以与SpringBoot的@ConditionalOnProperty，是由于我这进行了修改，初步解决了此问题）

而Nacos-Spring-Context中相关的bean，都是在这以后才被解析、装载进入Spring Container的，为何这么说？这里直接拉出官方对于ConfigurationClassPostProcessor的注释

* {@link BeanFactoryPostProcessor} used for bootstrapping processing of
* {@link Configuration @Configuration} classes.
*
* <p>Registered by default when using {@code <context:annotation-config/>} or
* {@code <context:component-scan/>}. Otherwise, may be declared manually as
* with any other BeanFactoryPostProcessor.
*
* <p>This post processor is priority-ordered as it is important that any
* {@link Bean} methods declared in {@code @Configuration} classes have
* their corresponding bean definitions registered before any other
* {@link BeanFactoryPostProcessor} executes.
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大体意思就是，ConfigurationClassPostProcessor的优先级是全部BeanFactoryPostProcessor实现中最高的，他必须在其余的BeanFactoryPostProcessor以前执行，由于其余的BeanFactoryPostProcessor须要ConfigurationClassPostProcessor进行解析装载进Spring Container。

解决方案

清楚该ISSUE为何会出现的缘由以后，那么相应的解决方案就很快的出来了。以前说到ConfigurationClassPostProcessor它会去解析@ConditionalOnProperty，而且它的执行先于其余的BeanFactoryPostProcessor实现；那么，还有什么比它先执行呢？

ApplicationContextInitializer

prepareContext(context, environment, listeners, applicationArguments, printedBanner);
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能够看出，ApplicationContextInitializer是在prepareContext执行的，而ConfigurationClassPostProcessor是在refreshContext执行的，所以，咱们只须要将配置拉取的代码提早到ApplicationContextInitializer中便可

@Override
public void initialize(ConfigurableApplicationContext context) {
    environment = context.getEnvironment();
    if (isEnable()) {
        CompositePropertySource compositePropertySource = new CompositePropertySource(NacosConfigConstants.NACOS_BOOTSTRAP_PROPERTY_APPLICATION);
        CacheableEventPublishingNacosServiceFactory singleton = CacheableEventPublishingNacosServiceFactory.getSingleton();
        singleton.setApplicationContext(context);
        String[] dataIds;
        String[] groupIds;
        String[] namespaces;
        try {
            dataIds = environment.getProperty(NacosConfigConstants.NACOS_CONFIG_DATA_ID, String[].class, new String[]{});
            groupIds = environment.getProperty(NacosConfigConstants.NACOS_CONFIG_GROUP_ID, String[].class, new String[dataIds.length]);
            namespaces = environment.getProperty(NacosProperties.NAMESPACE, String[].class, new String[dataIds.length]);

            for (int i = 0; i < dataIds.length; i ++) {
                Properties buildInfo = properties(namespaces[i]);
                ConfigService configService = singleton.createConfigService(buildInfo);

                String group = StringUtils.isEmpty(groupIds[i]) ? Constants.DEFAULT_GROUP : groupIds[i];
                String config = configService.getConfig(dataIds[i], group, 1000);
                if (config == null) {
                    logger.error("nacos-config-spring-boot : get config failed");
                    continue;
                }
                String name = buildDefaultPropertySourceName(dataIds[i], groupIds[i], buildInfo);
                NacosPropertySource nacosPropertySource = new NacosPropertySource(name, config);
                compositePropertySource.addPropertySource(nacosPropertySource);
            }
            environment.getPropertySources().addFirst(compositePropertySource);
        } catch (NacosException e) {
            logger.error(e.getErrMsg());
        }
    }
}
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