spring boot spring springcloud 微服务 【Nacos】@NacosValue的使用与原理

在SpringCloud工程中，可以使用@RefreshScope+@Value实现配置文件内容变更后的动态刷新。

在SpringBoot工程中，可以使用@NacosValue来实现配置文件内容变更后的动态刷新。

@NacosValue的使用

引入依赖：

com.alibaba.boot

nacos-config-spring-boot-starter

0.2.12

配置文件增加配置：

nacos:

config:

server-addr: 127.0.0.1:8848

bootstrap:

enable: true

log:

enable: true

data-id: order-service

type: yaml

auto-refresh: true # 开启自动刷新

@NacosValue的例子：

package com.morris.order.controller;

import com.alibaba.nacos.api.config.annotation.NacosValue;

import org.springframework.web.bind.annotation.GetMapping;

import org.springframework.web.bind.annotation.RequestMapping;

import org.springframework.web.bind.annotation.RestController;

@RestController

@RequestMapping("order")

public class NacosValueController {

@NacosValue(value = "${user.age}", autoRefreshed = true)

private Integer age2;

@GetMapping("age2")

public Integer getAge2() {

return age2;

}

}

注意在SpringCloud项目中不能使用@NacosValue注解，虽然这个注解存在，但是其源码的实现不存在。

@NacosValue源码分析

NacosConfigEnvironmentProcessor

NacosConfigEnvironmentProcessor实现了EnvironmentPostProcessor，会在SpringBoot项目启动时调用postProcessEnvironment()方法，去Nacos配置中心拉取配置。

需要在配置文件中开启预加载nacos.config.bootstrap.enable=true。

com.alibaba.boot.nacos.config.autoconfigure.NacosConfigEnvironmentProcessor#postProcessEnvironment

public void postProcessEnvironment(ConfigurableEnvironment environment,

SpringApplication application) {

application.addInitializers(new NacosConfigApplicationContextInitializer(this));

nacosConfigProperties = NacosConfigPropertiesUtils

.buildNacosConfigProperties(environment);

if (enable()) {

// nacos.config.bootstrap.enable=true

System.out.println(

"[Nacos Config Boot] : The preload log configuration is enabled");

loadConfig(environment);

NacosConfigLoader nacosConfigLoader = NacosConfigLoaderFactory.getSingleton(nacosConfigProperties, environment, builder);

LogAutoFreshProcess.build(environment, nacosConfigProperties, nacosConfigLoader, builder).process();

}

}

com.alibaba.boot.nacos.config.autoconfigure.NacosConfigEnvironmentProcessor#loadConfig

private void loadConfig(ConfigurableEnvironment environment) {

NacosConfigLoader configLoader = new NacosConfigLoader(nacosConfigProperties,

environment, builder);

configLoader.loadConfig();

// set defer NacosPropertySource

deferPropertySources.addAll(configLoader.getNacosPropertySources());

}

从配置中心拉取配置加入到Environment。 com.alibaba.boot.nacos.config.util.NacosConfigLoader#loadConfig

public void loadConfig() {

MutablePropertySources mutablePropertySources = environment.getPropertySources();

List sources = reqGlobalNacosConfig(globalProperties,

nacosConfigProperties.getType());

for (NacosConfigProperties.Config config : nacosConfigProperties.getExtConfig()) {

List elements = reqSubNacosConfig(config,

globalProperties, config.getType());

sources.addAll(elements);

}

if (nacosConfigProperties.isRemoteFirst()) {

// 默认为false，默认本地的配置优先级高

for (ListIterator itr = sources.listIterator(sources.size()); itr.hasPrevious();) {

mutablePropertySources.addAfter(

StandardEnvironment.SYSTEM_ENVIRONMENT_PROPERTY_SOURCE_NAME, itr.previous());

}

} else {

for (NacosPropertySource propertySource : sources) {

mutablePropertySources.addLast(propertySource);

}

}

}

NacosConfigApplicationContextInitializer

NacosConfigApplicationContextInitializer注册负责监听Nacos配置，实现自动刷新配置

com.alibaba.boot.nacos.config.autoconfigure.NacosConfigApplicationContextInitializer#initialize

public void initialize(ConfigurableApplicationContext context) {

singleton.setApplicationContext(context);

environment = context.getEnvironment();

nacosConfigProperties = NacosConfigPropertiesUtils

.buildNacosConfigProperties(environment);

final NacosConfigLoader configLoader = NacosConfigLoaderFactory.getSingleton(

nacosConfigProperties, environment, builder);

if (!enable()) {

logger.info("[Nacos Config Boot] : The preload configuration is not enabled");

}

else {

// If it opens the log level loading directly will cache

// DeferNacosPropertySource release

if (processor.enable()) {

// nacos.config.bootstrap.enable=true

processor.publishDeferService(context);

// 添加监听器

configLoader

.addListenerIfAutoRefreshed(processor.getDeferPropertySources());

}

else {

configLoader.loadConfig();

configLoader.addListenerIfAutoRefreshed();

}

}

final ConfigurableListableBeanFactory factory = context.getBeanFactory();

if (!factory

.containsSingleton(NacosBeanUtils.GLOBAL_NACOS_PROPERTIES_BEAN_NAME)) {

factory.registerSingleton(NacosBeanUtils.GLOBAL_NACOS_PROPERTIES_BEAN_NAME,

configLoader.getGlobalProperties());

}

}

遍历所有的Nacos配置文件，每个配置文件都添加一个监听器。 com.alibaba.boot.nacos.config.util.NacosConfigLoader#addListenerIfAutoRefreshed(java.util.List)

public void addListenerIfAutoRefreshed(

final List deferNacosPropertySources) {

for (DeferNacosPropertySource deferNacosPropertySource : deferNacosPropertySources) {

NacosPropertySourcePostProcessor.addListenerIfAutoRefreshed(

deferNacosPropertySource.getNacosPropertySource(),

deferNacosPropertySource.getProperties(),

deferNacosPropertySource.getEnvironment());

}

}

要实现配置的自动刷新，需要在配置文件中开启nacos.config.auto-refresh=true。 com.alibaba.nacos.spring.core.env.NacosPropertySourcePostProcessor#addListenerIfAutoRefreshed

public static void addListenerIfAutoRefreshed(

final NacosPropertySource nacosPropertySource, final Properties properties,

final ConfigurableEnvironment environment) {

// nacos.config.auto-refresh=true

if (!nacosPropertySource.isAutoRefreshed()) { // Disable Auto-Refreshed

return;

}

final String dataId = nacosPropertySource.getDataId();

final String groupId = nacosPropertySource.getGroupId();

final String type = nacosPropertySource.getType();

final NacosServiceFactory nacosServiceFactory = getNacosServiceFactoryBean(

beanFactory);

try {

ConfigService configService = nacosServiceFactory

.createConfigService(properties);

Listener listener = new AbstractListener() {

@Override

public void receiveConfigInfo(String config) {

String name = nacosPropertySource.getName();

NacosPropertySource newNacosPropertySource = new NacosPropertySource(

dataId, groupId, name, config, type);

newNacosPropertySource.copy(nacosPropertySource);

MutablePropertySources propertySources = environment

.getPropertySources();

// replace NacosPropertySource

// 监听事件的处理，直接替换Environment中的配置

propertySources.replace(name, newNacosPropertySource);

}

};

if (configService instanceof EventPublishingConfigService) {

// 通过EventPublishingConfigService进行代理

((EventPublishingConfigService) configService).addListener(dataId,

groupId, type, listener);

}

else {

configService.addListener(dataId, groupId, listener);

}

}

catch (NacosException e) {

throw new RuntimeException(

"ConfigService can't add Listener with properties : " + properties,

e);

}

}

通过EventPublishingConfigService添加监听器，里面对监听器做了一层包装。 com.alibaba.nacos.spring.context.event.config.EventPublishingConfigService#addListener(java.lang.String, java.lang.String, java.lang.String, com.alibaba.nacos.api.config.listener.Listener)

public void addListener(String dataId, String group, String type, Listener listener)

throws NacosException {

Listener listenerAdapter = new DelegatingEventPublishingListener(configService,

dataId, group, type, applicationEventPublisher, executor, listener);

addListener(dataId, group, listenerAdapter);

}

当配置中心的配置变更后，首先会回调DelegatingEventPublishingListener的receiveConfigInfo()，这里会调用被代理的监听器的receiveConfigInfo()，还会发布NacosConfigReceivedEvent事件。 com.alibaba.nacos.spring.context.event.config.DelegatingEventPublishingListener#receiveConfigInfo

public void receiveConfigInfo(String content) {

// 调用被代理的监听器的receiveConfigInfo()

onReceived(content);

// 发布NacosConfigReceivedEvent事件

publishEvent(content);

}

private void publishEvent(String content) {

NacosConfigReceivedEvent event = new NacosConfigReceivedEvent(configService,

dataId, groupId, content, configType);

applicationEventPublisher.publishEvent(event);

}

private void onReceived(String content) {

delegate.receiveConfigInfo(content);

}

NacosValueAnnotationBeanPostProcessor

postProcessPropertyValues()

NacosValueAnnotationBeanPostProcessor实现了InstantiationAwareBeanPostProcessorAdapter，其postProcessBeforeInitialization()方法会在Bean实例化之后和初始化之前执行，对Bean上加了@NacosValue注解的属性进行设置。

com.alibaba.spring.beans.factory.annotation.AbstractAnnotationBeanPostProcessor#postProcessPropertyValues

public PropertyValues postProcessPropertyValues(PropertyValues pvs, PropertyDescriptor[] pds, Object bean, String beanName) throws BeanCreationException {

// 查找@NacosVaLue注解的属性和方法

InjectionMetadata metadata = this.findInjectionMetadata(beanName, bean.getClass(), pvs);

try {

// 为属性设置值

metadata.inject(bean, beanName, pvs);

return pvs;

} catch (BeanCreationException var7) {

throw var7;

} catch (Throwable var8) {

throw new BeanCreationException(beanName, "Injection of @" + this.getAnnotationType().getSimpleName() + " dependencies is failed", var8);

}

}

postProcessBeforeInitialization()

NacosValueAnnotationBeanPostProcessor实现了BeanPostProcessor，其postProcessBeforeInitialization()方法会在Bean实例化之后和初始化之前执行，主要负责收集带有@NacosValue注解且需要自动刷新的属性。

如果属性需要自动刷新，需要设置@NacosValue的autoRefreshed为true。

com.alibaba.nacos.spring.context.annotation.config.NacosValueAnnotationBeanPostProcessor#postProcessBeforeInitialization

public Object postProcessBeforeInitialization(Object bean, final String beanName)

throws BeansException {

// 对Bean所有的属性进行处理

doWithFields(bean, beanName);

// 对Bean所有的方法进行处理

doWithMethods(bean, beanName);

return super.postProcessBeforeInitialization(bean, beanName);

}

private void doWithFields(final Object bean, final String beanName) {

ReflectionUtils.doWithFields(bean.getClass(),

new ReflectionUtils.FieldCallback() {

@Override

public void doWith(Field field) throws IllegalArgumentException {

NacosValue annotation = getAnnotation(field, NacosValue.class);

doWithAnnotation(beanName, bean, annotation, field.getModifiers(),

null, field);

}

});

}

private void doWithAnnotation(String beanName, Object bean, NacosValue annotation,

int modifiers, Method method, Field field) {

if (annotation != null) {

if (Modifier.isStatic(modifiers)) {

return;

}

if (annotation.autoRefreshed()) {

String placeholder = resolvePlaceholder(annotation.value());

if (placeholder == null) {

return;

}

NacosValueTarget nacosValueTarget = new NacosValueTarget(bean, beanName,

method, field, annotation.value());

// 将带有@NacosValue注解的属性加入到一个Map中

put2ListMap(placeholderNacosValueTargetMap, placeholder,

nacosValueTarget);

}

}

}

监听NacosConfigReceivedEvent

收到NacosConfigReceivedEvent事件时，通过反射调用上面收集好的属性和方法从而实现自动刷新。

com.alibaba.nacos.spring.context.annotation.config.NacosValueAnnotationBeanPostProcessor#onApplicationEvent

public void onApplicationEvent(NacosConfigReceivedEvent event) {

// In to this event receiver, the environment has been updated the

// latest configuration information, pull directly from the environment

// fix issue #142

for (Map.Entry> entry : placeholderNacosValueTargetMap

.entrySet()) {

String key = environment.resolvePlaceholders(entry.getKey());

String newValue = environment.getProperty(key);

if (newValue == null) {

continue;

}

List beanPropertyList = entry.getValue();

for (NacosValueTarget target : beanPropertyList) {

String md5String = MD5Utils.md5Hex(newValue, "UTF-8");

boolean isUpdate = !target.lastMD5.equals(md5String);

if (isUpdate) {

target.updateLastMD5(md5String);

Object evaluatedValue = resolveNotifyValue(target.nacosValueExpr, key, newValue);

if (target.method == null) {

setField(target, evaluatedValue);

}

else {

setMethod(target, evaluatedValue);

}

}

}

}

}

参考文章

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