上一篇博客写了SpringApplication.run(AuthServiceApplication.class, args); 的SpringApplication初始化，这一篇就写一下后面的run方法。
前言：写本篇博客前，我自己一步步的点进方法去看代码，乱糟糟的也不知道，代码都在做什么，反过来调过去的看了许久之后，发现，要想看懂SpringApplication的框架，首先最应该先了解的是 观察者模式，因为，在我的理解和查看中，又查阅不少博客，发现框架整体是用观察者来加载各个组件，达到灵活插拔的效果。观察者模式，请不太清楚的同学自行查阅，我这里给出简单的例子，就不再多做解释。
1 public class BaseEvent extends EventObject {
2 String name;
3
4 public BaseEvent(Object source, String name) {
5 super(source);
6 this.name = name;
7 }
8
9 public String getName() {
10 return name;
11 }
12 }
13
14 public interface BaseListener<T extends BaseEvent> extends EventListener {
15 void doEvent(T t);
16 }
17 public interface EventPublisher<T extends BaseEvent> {
18 abstract void publish(T event);
19 }
20 public class Event extends BaseEvent {
21 public Event(Object source, String name) {
22 super(source, name);
23 }
24 }
25 public class Listener implements BaseListener<Event> {
26
27 private String name;
28
29 public Listener(String name) {
30 this.name = name;
31 }
32 public Listener() {
33 }
34 @Override
35 public void doEvent(Event event) {
36 System.out.println("我是监听者："+this.name+",我监控到来自："+ event.getName()+",的event");
37 }
38
39 }
40 public class BaseEventPublisher<T extends BaseEvent> implements EventPublisher {
41
42 List<BaseListener<T>> listenerList = new ArrayList<>();
43
44 public List<BaseListener<T>> getListenerList() {
45 return listenerList;
46 }
47
48 @Override
49 public void publish(BaseEvent event) {
50 if (!CollectionUtils.isEmpty(listenerList)) {
51 for (BaseListener listener:listenerList) {
52 listener.doEvent((T) event);
53 }
54 }
55 }
56 }
57
58
59 BaseEvent eventA = new Event("","eventA");
60 BaseEventPublisher publisher = new BaseEventPublisher();
61 BaseListener<Event> listenerA = new Listener("listenerA");
62 BaseListener<Event> listenerB = new Listener("listenerB");
63 publisher.getListenerList().add(listenerA);
64 publisher.getListenerList().add(listenerB);
65 publisher.publish(eventA);
大家可以自行运行一下，理解一下观察者模式的思维。
--------------------
下面就写一下我自己看源码的理解
1 public ConfigurableApplicationContext run(String... args) {
2 StopWatch stopWatch = new StopWatch();//用来输出所包含的代码运行完消耗的时间，可自行查阅相关用法，不再此赘述
3 stopWatch.start();
4 ConfigurableApplicationContext context = null;
5 Collection<SpringBootExceptionReporter> exceptionReporters = new ArrayList<>();
6 configureHeadlessProperty();
7 SpringApplicationRunListeners listeners = getRunListeners(args);//获取上面博客所述的配置在spring.factories的监听者
8 listeners.starting();//这里就开始了观察者模式
9 try {
10 ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);
11 ConfigurableEnvironment environment = prepareEnvironment(listeners, applicationArguments);//准备运行的环境信息
12 configureIgnoreBeanInfo(environment);//配置忽略
13 Banner printedBanner = printBanner(environment);
14 context = createApplicationContext();//创建上下文
15 exceptionReporters = getSpringFactoriesInstances(SpringBootExceptionReporter.class,
16 new Class[] { ConfigurableApplicationContext.class }, context);
17 prepareContext(context, environment, listeners, applicationArguments, printedBanner);//准备上下文
18 refreshContext(context);//刷新上下文
19 afterRefresh(context, applicationArguments);
20 stopWatch.stop();
21 if (this.logStartupInfo) {
22 new StartupInfoLogger(this.mainApplicationClass).logStarted(getApplicationLog(), stopWatch);
23 }
24 listeners.started(context);//启动上下文
25 callRunners(context, applicationArguments);//通知所有的线程开始运行
26 }
27 catch (Throwable ex) {
28 handleRunFailure(context, ex, exceptionReporters, listeners);
29 throw new IllegalStateException(ex);
30 }
31
32 try {
33 listeners.running(context);//运行
34 }
35 catch (Throwable ex) {
36 handleRunFailure(context, ex, exceptionReporters, null);
37 throw new IllegalStateException(ex);
38 }
39 return context;
40 }
上面代码段，先着重讲一下第八行，listeners.starting();因为后面很多代码内部都和这一行运行的代码类似
void starting() {
for (SpringApplicationRunListener listener : this.listeners) {
listener.starting();
}
}
1 public void starting() {
2 this.initialMulticaster.multicastEvent(new ApplicationStartingEvent(this.application, this.args));
3 }
initialMulticaster，多路广播器。通知所有监听者，接到广播的就要运行了。multicastEvent代码如下
public void multicastEvent(final ApplicationEvent event, @Nullable ResolvableType eventType) {
ResolvableType type = (eventType != null ? eventType : resolveDefaultEventType(event));
Executor executor = getTaskExecutor();
for (ApplicationListener<?> listener : getApplicationListeners(event, type)) {
if (executor != null) {
executor.execute(() -> invokeListener(listener, event));
}
else {
invokeListener(listener, event);
}
}
}
下面进入invokeListener
1 private void doInvokeListener(ApplicationListener listener, ApplicationEvent event) {
2 try {
3 listener.onApplicationEvent(event);//划重点
4 }
5 catch (ClassCastException ex) {
6 String msg = ex.getMessage();
7 if (msg == null || matchesClassCastMessage(msg, event.getClass())) {
8 // Possibly a lambda-defined listener which we could not resolve the generic event type for
9 // -> let's suppress the exception and just log a debug message.
10 Log logger = LogFactory.getLog(getClass());
11 if (logger.isTraceEnabled()) {
12 logger.trace("Non-matching event type for listener: " + listener, ex);
13 }
14 }
15 else {
16 throw ex;
17 }
18 }
19 }
listener.onApplicationEvent(event);此方法运行实现了 org.springframework.context.ApplicationListener类的onApplicationEvent方法。
整个框架多处使用，广播和监听机制，*的配置监听者。各个组件，配置自己的监听者，达到*扩展的目的。