配置文件的动态更新
通常获取配置文件的方式
1, @Value
2. @ConfigurationProperties(Prefix)
如果是在运行时要动态更新的话，
第一种方式要在bean上加@RefreshScope
第二种方式是自动支持的。
以Nacos为为例，我们可以看下源码是如何实现的：
Nacos获取配置中心是通过单独一个线程的长轮询获取的:
com.alibaba.nacos.client.config.impl.ClientWorker.LongPollingRunnable
当获取到更新配置后，publishEvent
org.springframework.cloud.alibaba.nacos.refresh.NacosContextRefresher#registerNacosListener
private void registerNacosListener(final String group, final String dataId) {
Listener listener = listenerMap.computeIfAbsent(dataId, i -> new Listener() {
@Override
public void receiveConfigInfo(String configInfo) {
refreshCountIncrement();
String md5 = "";
if (!StringUtils.isEmpty(configInfo)) {
try {
MessageDigest md = MessageDigest.getInstance("MD5");
md5 = new BigInteger(1, md.digest(configInfo.getBytes("UTF-8")))
.toString(16);
}
catch (NoSuchAlgorithmException | UnsupportedEncodingException e) {
log.warn("[Nacos] unable to get md5 for dataId: " + dataId, e);
}
}
refreshHistory.add(dataId, md5);
applicationContext.publishEvent(
new RefreshEvent(this, null, "Refresh Nacos config"));
if (log.isDebugEnabled()) {
log.debug("Refresh Nacos config group " + group + ",dataId" + dataId);
}
}
@Override
public Executor getExecutor() {
return null;
}
});
try {
configService.addListener(dataId, group, listener);
}
catch (NacosException e) {
e.printStackTrace();
}
}
当收到{@link RefreshEvent}时调用{@link RefreshEventListener#refresh}。
只在收到{@link ApplicationReadyEvent}后响应{@link RefreshEvent}，
因为RefreshEvents可能在应用程序生命周期中来得太早。（译文）
public class RefreshEventListener implements SmartApplicationListener {
private static Log log = LogFactory.getLog(RefreshEventListener.class);
private ContextRefresher refresh;
private AtomicBoolean ready = new AtomicBoolean(false);
public RefreshEventListener(ContextRefresher refresh) {
this.refresh = refresh;
}
@Override
public boolean supportsEventType(Class<? extends ApplicationEvent> eventType) {
return ApplicationReadyEvent.class.isAssignableFrom(eventType)
|| RefreshEvent.class.isAssignableFrom(eventType);
}
@Override
public void onApplicationEvent(ApplicationEvent event) {
if (event instanceof ApplicationReadyEvent) {
handle((ApplicationReadyEvent) event);
}
else if (event instanceof RefreshEvent) {
handle((RefreshEvent) event);
}
}
public void handle(ApplicationReadyEvent event) {
this.ready.compareAndSet(false, true);
}
public void handle(RefreshEvent event) {
if (this.ready.get()) { // don't handle events before app is ready
log.debug("Event received " + event.getEventDesc());
Set<String> keys = this.refresh.refresh();
log.info("Refresh keys changed: " + keys);
}
}
}
org.springframework.cloud.context.refresh.ContextRefresher
public synchronized Set<String> refresh() {
Set<String> keys = refreshEnvironment();
this.scope.refreshAll();
return keys;
}
public synchronized Set<String> refreshEnvironment() {
Map<String, Object> before = extract(
this.context.getEnvironment().getPropertySources());
addConfigFilesToEnvironment();
Set<String> keys = changes(before,
extract(this.context.getEnvironment().getPropertySources())).keySet();
this.context.publishEvent(new EnvironmentChangeEvent(this.context, keys));
return keys;
}
ConfigurableApplicationContext addConfigFilesToEnvironment() {
ConfigurableApplicationContext capture = null;
try {
StandardEnvironment environment = copyEnvironment(
this.context.getEnvironment());
SpringApplicationBuilder builder = new SpringApplicationBuilder(Empty.class)
.bannerMode(Mode.OFF).web(WebApplicationType.NONE)
.environment(environment);
// Just the listeners that affect the environment (e.g. excluding logging
// listener because it has side effects)
builder.application()
.setListeners(Arrays.asList(new BootstrapApplicationListener(),
new ConfigFileApplicationListener()));
capture = builder.run();
if (environment.getPropertySources().contains(REFRESH_ARGS_PROPERTY_SOURCE)) {
environment.getPropertySources().remove(REFRESH_ARGS_PROPERTY_SOURCE);
}
MutablePropertySources target = this.context.getEnvironment()
.getPropertySources();
String targetName = null;
for (PropertySource<?> source : environment.getPropertySources()) {
String name = source.getName();
if (target.contains(name)) {
targetName = name;
}
if (!this.standardSources.contains(name)) {
if (target.contains(name)) {
target.replace(name, source);
}
else {
if (targetName != null) {
target.addAfter(targetName, source);
}
else {
// targetName was null so we are at the start of the list
target.addFirst(source);
targetName = name;
}
}
}
}
}
finally {
ConfigurableApplicationContext closeable = capture;
while (closeable != null) {
try {
closeable.close();
}
catch (Exception e) {
// Ignore;
}
if (closeable.getParent() instanceof ConfigurableApplicationContext) {
closeable = (ConfigurableApplicationContext) closeable.getParent();
}
else {
break;
}
}
}
return capture;
}
然后就重新走了一次启动的流程
/**
* Run the Spring application, creating and refreshing a new
* {@link ApplicationContext}.
* @param args the application arguments (usually passed from a Java main method)
* @return a running {@link ApplicationContext}
*/
public ConfigurableApplicationContext run(String... args) {
StopWatch stopWatch = new StopWatch();
stopWatch.start();
ConfigurableApplicationContext context = null;
Collection<SpringBootExceptionReporter> exceptionReporters = new ArrayList<>();
configureHeadlessProperty();
SpringApplicationRunListeners listeners = getRunListeners(args);
listeners.starting();
try {
ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);
ConfigurableEnvironment environment = prepareEnvironment(listeners, applicationArguments);
configureIgnoreBeanInfo(environment);
Banner printedBanner = printBanner(environment);
context = createApplicationContext();
exceptionReporters = getSpringFactoriesInstances(SpringBootExceptionReporter.class,
new Class[] { ConfigurableApplicationContext.class }, context);
prepareContext(context, environment, listeners, applicationArguments, printedBanner);
refreshContext(context);
afterRefresh(context, applicationArguments);
stopWatch.stop();
if (this.logStartupInfo) {
new StartupInfoLogger(this.mainApplicationClass).logStarted(getApplicationLog(), stopWatch);
}
listeners.started(context);
callRunners(context, applicationArguments);
}
catch (Throwable ex) {
handleRunFailure(context, ex, exceptionReporters, listeners);
throw new IllegalStateException(ex);
} try {
listeners.running(context);
}
catch (Throwable ex) {
handleRunFailure(context, ex, exceptionReporters, null);
throw new IllegalStateException(ex);
}
return context;
}
org.springframework.cloud.context.properties.ConfigurationPropertiesRebinder#onApplicationEvent
public void onApplicationEvent(EnvironmentChangeEvent event) {
if (this.applicationContext.equals(event.getSource())
// Backwards compatible
|| event.getKeys().equals(event.getSource())) {
rebind();
}
}
ConfigurationPropertiesRebinder 看见这个名字就知道是怎么回事了。
找到所有的ConfigurationPropertiesBeans, 遍历它们
@ManagedOperation
public void rebind() {
this.errors.clear();
for (String name : this.beans.getBeanNames()) {
rebind(name);
}
} @ManagedOperation
public boolean rebind(String name) {
if (!this.beans.getBeanNames().contains(name)) {
return false;
}
if (this.applicationContext != null) {
try {
Object bean = this.applicationContext.getBean(name);
if (AopUtils.isAopProxy(bean)) {
bean = ProxyUtils.getTargetObject(bean);
}
if (bean != null) {
this.applicationContext.getAutowireCapableBeanFactory()
.destroyBean(bean);
this.applicationContext.getAutowireCapableBeanFactory()
.initializeBean(bean, name);
return true;
}
}
catch (RuntimeException e) {
this.errors.put(name, e);
throw e;
}
catch (Exception e) {
this.errors.put(name, e);
throw new IllegalStateException("Cannot rebind to " + name, e);
}
}
return false;
}
org.springframework.boot.context.properties.ConfigurationPropertiesBindingPostProcessor#postProcessBeforeInitialization
@Override
public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
ConfigurationProperties annotation = getAnnotation(bean, beanName, ConfigurationProperties.class);
if (annotation != null) {
bind(bean, beanName, annotation);
}
return bean;
}
这个BeanPostProcessor里就对我们要更新的Bean进行更新最新的配置值了。如下列如红色部分
private void bind(Object bean, String beanName, ConfigurationProperties annotation) {
ResolvableType type = getBeanType(bean, beanName);
Validated validated = getAnnotation(bean, beanName, Validated.class);
Annotation[] annotations = (validated != null) ? new Annotation[] { annotation, validated }
: new Annotation[] { annotation };
Bindable<?> target = Bindable.of(type).withExistingValue(bean).withAnnotations(annotations);
try {
this.configurationPropertiesBinder.bind(target);
}
catch (Exception ex) {
throw new ConfigurationPropertiesBindException(beanName, bean, annotation, ex);
}
}