SpringBoot中内置的监听器
内置监听器都定义在在spring.factories文件中
| 监听器 | 监听事件 | 说明 |
|---|---|---|
| ClearCachesApplicationListener | ContextRefreshedEvent | 当触发ContextRefreshedEvent事件会清空应用的缓存 |
| ParentContextCloserApplicationListener | ParentContextAvailableEvent | 触发ParentContextAvailableEvent事件会完成父容器关闭的监听器 |
| CloudFoundryVcapEnvironmentPostProcessor | ApplicationPreparedEvent | 判断环境中是否存在VCAP_APPLICATION或者VCAP_SERVICES。如果有就添加Cloud Foundry的配置；没有就不执行任何操作。 |
| FileEncodingApplicationListener | ApplicationEnvironmentPreparedEvent | 文件编码的监听器 |
| AnsiOutputApplicationListener | ApplicationEnvironmentPreparedEvent | 根据 spring.output.ansi.enabled参数配置 AnsiOutput |
| ConfigFileApplicationListener | ApplicationEnvironmentPreparedEventApplicationPreparedEvent | 完成相关属性文件的加载，application.properties、 application.yml |
| DelegatingApplicationListener | ApplicationEnvironmentPreparedEvent | 监听到事件后转发给环境变量 context.listener.classes指定的那些事件监听器 |
| ClasspathLoggingApplicationListener | ApplicationEnvironmentPreparedEventApplicationFailedEvent | 一个SmartApplicationListener,对环境就绪事件ApplicationEnvironmentPreparedEvent/应用失败事件ApplicationFailedEvent做出响应，往日志DEBUG级别输出TCCL(thread context class loader)的classpath。 |
| LoggingApplicationListener | ApplicationStartingEvent ApplicationEnvironmentPreparedEvent ApplicationPreparedEventContextClosedEventApplicationFailedEvent | 配置 LoggingSystem。使用 logging.config环境变量指定的配置或者缺省配置 |
| LiquibaseServiceLocatorApplicationListener | ApplicationStartingEvent | 使用一个可以和Spring Boot可执行jar包配合工作的版本替换liquibase ServiceLocator |
| BackgroundPreinitializer | ApplicationStartingEventApplicationReadyEventApplicationFailedEvent | 尽早触发一些耗时的初始化任务，使用一个后台线程 |
自定义监听器和监听事件
自定义监听事件
需要继承ApplicationEvent
public class MyEvent extends ApplicationEvent {
/**
* Create a new {@code ApplicationEvent}.
*
* @param source the object on which the event initially occurred or with
* which the event is associated (never {@code null})
*/
public MyEvent(Object source) {
super(source);
}
}
自定义监听器
需要实现ApplicationListener接口
/**
* @author 26917
* 自定义监听器
* 监听自定义的事件
*/
public class MyCustomerEventListener implements ApplicationListener<MyEvent> {
@Override
public void onApplicationEvent(MyEvent event) {
System.out.println("MyCustomerEventListener ----》 自定义事件触发" + event);
}
}
ApplicationListener类图
将这个自定义的监听器加入到spring.factories文件中
org.springframework.context.ApplicationListener=\
com.nyc.listener.MyCustomerEventListener
使用这个监听器
@RestController
public class UserController {
@Autowired
private ApplicationContext context;
@GetMapping("/hello")
public String hello(){
context.publishEvent(new MyEvent(new Object()));
return "hello";
}
}
监听器代码分析
类图分析
getRunListeners(args)方法
这个方法获取到事件发布器
EventPublishingRunListener 构造方法
public EventPublishingRunListener(SpringApplication application, String[] args) {
this.application = application;
this.args = args;
// 初始化多个监听器，其实就是我们前面加载的spring.factories文件中的11个监听器
this.initialMulticaster = new SimpleApplicationEventMulticaster();
// application.getListeners() 获取11个监听器
for (ApplicationListener<?> listener : application.getListeners()) {
// 绑定初始的11个监听器
this.initialMulticaster.addApplicationListener(listener);
}
}
listeners.starting()方法
触发启动事件 -》发布starting事件，那么监听starting事件的监听器就会触发
class SpringApplicationRunListeners {
private final Log log;
private final List<SpringApplicationRunListener> listeners;
SpringApplicationRunListeners(Log log, Collection<? extends SpringApplicationRunListener> listeners) {
this.log = log;
this.listeners = new ArrayList<>(listeners);
}
void starting() {
// 发布器 EventPublishingRunListener
for (SpringApplicationRunListener listener : this.listeners) {
listener.starting();
}
}
void environmentPrepared(ConfigurableEnvironment environment) {
for (SpringApplicationRunListener listener : this.listeners) {
listener.environmentPrepared(environment);
}
}
void contextPrepared(ConfigurableApplicationContext context) {
for (SpringApplicationRunListener listener : this.listeners) {
listener.contextPrepared(context);
}
}
void contextLoaded(ConfigurableApplicationContext context) {
for (SpringApplicationRunListener listener : this.listeners) {
listener.contextLoaded(context);
}
}
void started(ConfigurableApplicationContext context) {
for (SpringApplicationRunListener listener : this.listeners) {
listener.started(context);
}
}
void running(ConfigurableApplicationContext context) {
for (SpringApplicationRunListener listener : this.listeners) {
listener.running(context);
}
}
void failed(ConfigurableApplicationContext context, Throwable exception) {
for (SpringApplicationRunListener listener : this.listeners) {
callFailedListener(listener, context, exception);
}
}
private void callFailedListener(SpringApplicationRunListener listener, ConfigurableApplicationContext context,
Throwable exception) {
try {
listener.failed(context, exception);
}
catch (Throwable ex) {
if (exception == null) {
ReflectionUtils.rethrowRuntimeException(ex);
}
if (this.log.isDebugEnabled()) {
this.log.error("Error handling failed", ex);
}
else {
String message = ex.getMessage();
message = (message != null) ? message : "no error message";
this.log.warn("Error handling failed (" + message + ")");
}
}
}
}
SpringApplicationRunListeners类的作用
SpringApplicationRunListener 的集合代理类，用来统一调度并触发所有 RunListener，整体监视 Spring Boot 启动过程的各个阶段。
在源码中SpringApplicationRunListener接口的默认实现就只有，EventPublishingRunListener
EventPublishingRunListener类的starting方法。
@Override
public void starting() {
this.initialMulticaster.multicastEvent(new ApplicationStartingEvent(this.application, this.args));
}
在springboot的启动的时候会在以下几个阶段进行监听器发布，分别是启动阶段、环境配置准备阶段、容器上下文准备阶段、启动完成阶段、启动失败阶段以及运行阶段。
