这篇文档主要关注下配置修改后对应的 Java 对象是如何更新，并不关注整体的配置改动流程
所有代码都来自 apollo-client 项目
更新流程
在 Apollo 控制台进行配置修改并发布后，对应的 client 端拉取到更新后，会调用到 com.ctrip.framework.apollo.spring.property.AutoUpdateConfigChangeListener#onChange 方法
在调用 onChange 会收到对应的修改的配置信息 ConfigChangeEvent， 其中包含改动的 key 和 value, 则改动流程如下：
- 根据改动的配置的 key 从 springValueRegistry 找到对应的关联到这个 key 的 Spring Bean 信息，如果找不到则不处理 根据找到的 Spring Bean 信息，进行对应关联配置的更新
在第二步中会判断关联配置是用过属性关联还是方法进行关联的，代码如下
public void update(Object newVal) throws IllegalAccessException, InvocationTargetException { if (isField()) { injectField(newVal); } else { injectMethod(newVal); }}
在上面的问题中，还有两个问题存疑
- 如何通过 key 找到对应的 Spring Bean 信息 如何将 Apollo 的配置值转换为 Spring 的识别的值
public class AutoUpdateConfigChangeListener implements ConfigChangeListener{ private static final Logger logger = LoggerFactory.getLogger(AutoUpdateConfigChangeListener.class); private final boolean typeConverterHasConvertIfNecessaryWithFieldParameter; private final Environment environment; private final ConfigurableBeanFactory beanFactory; private final TypeConverter typeConverter; private final PlaceholderHelper placeholderHelper; private final SpringValueRegistry springValueRegistry; private final Gson gson; public AutoUpdateConfigChangeListener(Environment environment, ConfigurableListableBeanFactory beanFactory){ this.typeConverterHasConvertIfNecessaryWithFieldParameter = testTypeConverterHasConvertIfNecessaryWithFieldParameter(); this.beanFactory = beanFactory; this.typeConverter = this.beanFactory.getTypeConverter(); this.environment = environment; this.placeholderHelper = SpringInjector.getInstance(PlaceholderHelper.class); this.springValueRegistry = SpringInjector.getInstance(SpringValueRegistry.class); this.gson = new Gson(); } @Override public void onChange(ConfigChangeEvent changeEvent) { Set<String> keys = changeEvent.changedKeys(); if (CollectionUtils.isEmpty(keys)) { return; } for (String key : keys) { // 1. check whether the changed key is relevant Collection<SpringValue> targetValues = springValueRegistry.get(beanFactory, key); if (targetValues == null || targetValues.isEmpty()) { continue; } // 2. update the value for (SpringValue val : targetValues) { updateSpringValue(val); } } } private void updateSpringValue(SpringValue springValue) { try { Object value = resolvePropertyValue(springValue); springValue.update(value); logger.info("Auto update apollo changed value successfully, new value: {}, {}", value, springValue); } catch (Throwable ex) { logger.error("Auto update apollo changed value failed, {}", springValue.toString(), ex); } } /** * Logic transplanted from DefaultListableBeanFactory * @see org.springframework.beans.factory.support.DefaultListableBeanFactory#doResolveDependency(org.springframework.beans.factory.config.DependencyDescriptor, java.lang.String, java.util.Set, org.springframework.beans.TypeConverter) */ private Object resolvePropertyValue(SpringValue springValue) { // value will never be null, as @Value and @ApolloJsonValue will not allow that Object value = placeholderHelper .resolvePropertyValue(beanFactory, springValue.getBeanName(), springValue.getPlaceholder()); if (springValue.isJson()) { value = parseJsonValue((String)value, springValue.getGenericType()); } else { if (springValue.isField()) { // org.springframework.beans.TypeConverter#convertIfNecessary(java.lang.Object, java.lang.Class, java.lang.reflect.Field) is available from Spring 3.2.0+ if (typeConverterHasConvertIfNecessaryWithFieldParameter) { value = this.typeConverter .convertIfNecessary(value, springValue.getTargetType(), springValue.getField()); } else { value = this.typeConverter.convertIfNecessary(value, springValue.getTargetType()); } } else { value = this.typeConverter.convertIfNecessary(value, springValue.getTargetType(), springValue.getMethodParameter()); } } return value; } private Object parseJsonValue(String json, Type targetType) { try { return gson.fromJson(json, targetType); } catch (Throwable ex) { logger.error("Parsing json '{}' to type {} failed!", json, targetType, ex); throw ex; } } private boolean testTypeConverterHasConvertIfNecessaryWithFieldParameter() { try { TypeConverter.class.getMethod("convertIfNecessary", Object.class, Class.class, Field.class); } catch (Throwable ex) { return false; } return true; }}
如何将配置 key 和 Spring Bean 关联起来
在 Spring 常见配置包括 2 种
public class ApiConfig { // 1. 直接在 Field 是进行注入 @Value("${feifei.appId}") protected String appId; protected String predUrl; // 2. 在方法上进行注入 @Value("${predUrl}") public void setPredUrl(String predUrl) { this.predUrl = predUrl; }}
在 Apollo 代码中，通过实现 BeanPostProcessor 接口来检测所有的Spring Bean 的创建过程，在 Spring Bean 创建的过程中会调用对应的 org.springframework.beans.factory.config.BeanPostProcessor#postProcessBeforeInitialization 和 org.springframework.beans.factory.config.BeanPostProcessor#postProcessAfterInitialization 方法。
Apollo 通过在 Bean 生成过程中，检测 Bean 类中属性和方法是否存在 @Value 注解，如果存在，提出其中的 key, 其处理方法在 processField 和 processMethod 分别处理 Field 和 Method 中可能出现的 @Value 注解。如果存在注解则将对应的信息存到 SpringValue 对应 springValueRegistry 全局对象中，方便在其它地方可以直接获取。
在属性除了通过 @Value 注入，也可以用过 xml 进行配置，在这种情况通过 processBeanPropertyValues 方法来处理
通过两种处理方式就可以将 key 和对应的 Spring Bean 信息关联起来
public class SpringValueProcessor extends ApolloProcessor implements BeanFactoryPostProcessor, BeanFactoryAware { private static final Logger logger = LoggerFactory.getLogger(SpringValueProcessor.class); private final ConfigUtil configUtil; private final PlaceholderHelper placeholderHelper; private final SpringValueRegistry springValueRegistry; private BeanFactory beanFactory; private Multimap<String, SpringValueDefinition> beanName2SpringValueDefinitions; public SpringValueProcessor() { configUtil = ApolloInjector.getInstance(ConfigUtil.class); placeholderHelper = SpringInjector.getInstance(PlaceholderHelper.class); springValueRegistry = SpringInjector.getInstance(SpringValueRegistry.class); beanName2SpringValueDefinitions = LinkedListMultimap.create(); } @Override public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException { if (configUtil.isAutoUpdateInjectedSpringPropertiesEnabled() && beanFactory instanceof BeanDefinitionRegistry) { beanName2SpringValueDefinitions = SpringValueDefinitionProcessor .getBeanName2SpringValueDefinitions((BeanDefinitionRegistry) beanFactory); } } @Override public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException { if (configUtil.isAutoUpdateInjectedSpringPropertiesEnabled()) { super.postProcessBeforeInitialization(bean, beanName); processBeanPropertyValues(bean, beanName); } return bean; } @Override protected void processField(Object bean, String beanName, Field field) { // register @Value on field Value value = field.getAnnotation(Value.class); if (value == null) { return; } Set<String> keys = placeholderHelper.extractPlaceholderKeys(value.value()); if (keys.isEmpty()) { return; } for (String key : keys) { SpringValue springValue = new SpringValue(key, value.value(), bean, beanName, field, false); springValueRegistry.register(beanFactory, key, springValue); logger.debug("Monitoring {}", springValue); } } @Override protected void processMethod(Object bean, String beanName, Method method) { //register @Value on method Value value = method.getAnnotation(Value.class); if (value == null) { return; } //skip Configuration bean methods if (method.getAnnotation(Bean.class) != null) { return; } if (method.getParameterTypes().length != 1) { logger.error("Ignore @Value setter {}.{}, expecting 1 parameter, actual {} parameters", bean.getClass().getName(), method.getName(), method.getParameterTypes().length); return; } Set<String> keys = placeholderHelper.extractPlaceholderKeys(value.value()); if (keys.isEmpty()) { return; } for (String key : keys) { SpringValue springValue = new SpringValue(key, value.value(), bean, beanName, method, false); springValueRegistry.register(beanFactory, key, springValue); logger.info("Monitoring {}", springValue); } } private void processBeanPropertyValues(Object bean, String beanName) { Collection<SpringValueDefinition> propertySpringValues = beanName2SpringValueDefinitions .get(beanName); if (propertySpringValues == null || propertySpringValues.isEmpty()) { return; } for (SpringValueDefinition definition : propertySpringValues) { try { PropertyDescriptor pd = BeanUtils .getPropertyDescriptor(bean.getClass(), definition.getPropertyName()); Method method = pd.getWriteMethod(); if (method == null) { continue; } SpringValue springValue = new SpringValue(definition.getKey(), definition.getPlaceholder(), bean, beanName, method, false); springValueRegistry.register(beanFactory, definition.getKey(), springValue); logger.debug("Monitoring {}", springValue); } catch (Throwable ex) { logger.error("Failed to enable auto update feature for {}.{}", bean.getClass(), definition.getPropertyName()); } } // clear beanName2SpringValueDefinitions.removeAll(beanName); } @Override public void setBeanFactory(BeanFactory beanFactory) throws BeansException { this.beanFactory = beanFactory; }}
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