最近工作过程中遇到了标题中的错误，导致整个项目都不可以访问；原因是我修改了consul的配置，修改过后由于consul监控配置开关是打开着的，所以监控到配置做了修改后会重新创建ApplicationContext对象，并且会将之前的ApplicationContext对象销毁调；由于我在项目启动的时候初始化了一个ApplicationContext全局变量，会在项目中AOP记录访问日志的时候使用，所以每个接口都会报标题中的错误；
一、原因分析
- Consul配置监控类ConfigWatch监控consul配置中心的配置变动，如果配置有变动会触发RefreshEvent事件
@Timed("consul.watch-config-keys")
public void watchConfigKeyValues() {
if (!this.running.get()) {
return;
}
for (String context : this.consulIndexes.keySet()) {
//********
RefreshEventData data = new RefreshEventData(context, currentIndex, newIndex);
//配置有变动，触发RefreshEvent事件
this.publisher.publishEvent(new RefreshEvent(this, data, data.toString()));
//*****
}
this.firstTime = false;
}
- RefreshEventListener监听器监听RefreshEvent事件，并创建新的ApplicationContext对象，销毁原来的ApplicationContext对象
@Override
public void onApplicationEvent(ApplicationEvent event) {
if (event instanceof ApplicationReadyEvent) {
handle((ApplicationReadyEvent) event);
}
else if (event instanceof RefreshEvent) {
//监听RefreshEvent事件
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());
// 触发ContextRefresher类的refresh方法来创建ApplicationContext对象
Set<String> keys = this.refresh.refresh();
log.info("Refresh keys changed: " + keys);
}
}
- ContextRefresher类新建ApplicationContext并发送EnvironmentChangeEvent事件
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());
updateEnvironment();
Set<String> keys = changes(before, extract(this.context.getEnvironment().getPropertySources())).keySet();
//触发EnvironmentChangeEvent事件，可以在此事件的监听器来修改重建后的ApplicationContext
this.context.publishEvent(new EnvironmentChangeEvent(this.context, keys));
return keys;
}
//此方法的实现(LegacyContextRefresher.updateEnvironment)是真正用来新建ApplicationContext和销毁原来ApplicationContext的
protected abstract void updateEnvironment();
- LegacyContextRefresher.updateEnvironment实现
public class LegacyContextRefresher extends ContextRefresher {
@Deprecated
public LegacyContextRefresher(ConfigurableApplicationContext context, RefreshScope scope) {
super(context, scope);
}
public LegacyContextRefresher(ConfigurableApplicationContext context, RefreshScope scope,
RefreshAutoConfiguration.RefreshProperties properties) {
super(context, scope, properties);
}
@Override
protected void updateEnvironment() {
addConfigFilesToEnvironment();
}
/* For testing. */ ConfigurableApplicationContext addConfigFilesToEnvironment() {
ConfigurableApplicationContext capture = null;
try {
//*****************省略*******************
SpringApplicationBuilder builder = new SpringApplicationBuilder(Empty.class).bannerMode(Banner.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 BootstrapConfigFileApplicationListener()));
// 新建ApplicationContext对象，实际会进入org.springframework.boot.builder.SpringApplicationBuilder#run方法创建；
capture = builder.run();
//*************省略**********************
}
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;
}
}
上述builder.run方法会进入org.springframework.boot.builder.SpringApplicationBuilder#run最终是在org.springframework.boot.SpringApplication#run(java.lang.String…)方法中创建：
二、解决方案
在原因分析中我们知道新建ApplicationContext后会发送EnvironmentChangeEvent事件，而EnvironmentChangeEvent事件会接收一个ApplicationContext作为参数，我们的解决方案就是监听EnvironmentChangeEvent事件，修改定义的全局变量；
方案一：使用@RabbitListener注解监听EnvironmentChangeEvent事件
@EventListener
public void handler(EnvironmentChangeEvent event){
ApplicationContext context = (ApplicationContext) event.getSource();
//修改定义的全局ApplicationContext对象
IOCContext.setCONTEXT(context);
System.out.println(event.getSource());
}
此方案适用于具体项目之中，如果想用在springboot脚手架类SDK中，这种方案就行不通了；
方案二：定义实现ApplicationListener监听器接口类
public class EnvironmentChangeApplicationListener implements ApplicationListener<EnvironmentChangeEvent> {
@Override
public void onApplicationEvent(EnvironmentChangeEvent event) {
Object source = event.getSource();
if (Objects.isNull(source) || !(source instanceof ApplicationContext)) {
return;
}
IOCContext.setCONTEXT((ApplicationContext) source);
}
}