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
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：
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
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;
}
}
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;
}
}
