EventBus 3之源码分析

eventbus 2的源码分析：https://blog.csdn.net/qq_35559358/article/details/74295870

请看本篇的朋友先看2从更基础更详细的地方理解，篇末将加入2个版本源码中最大不同实现的对比，新人菜鸟，请不要骂太凶。

本篇的分析和eventbus 2有很多相同的，借用原作者的博客，说明大部分逻辑。

转载自：

https://xudeveloper.github.io/2018/01/20/EventBus%203.1.1%20%E6%BA%90%E7%A0%81%E8%A7%A3%E6%9E%90/

一、本文需要解决的问题

我研究EventBus源码的目的是解决以下几个我在使用过程中所思考的问题：

1. 这个框架涉及到一种设计模式叫做观察者模式，什么是观察者模式？
2. 事件如何进行定义，有没有相关限制？
3. 观察者绑定观察事件的时候，绑定方法的命名有限制吗？
4. 事件发送和接收的原理？

二、初步使用

为了研究源码的方便，我写了一个简单的demo。

定义事件

TestEvent.java：

public class TestEvent {
private String msg;
public String getMsg() {
return msg;
}
public void setMsg(String msg) {
this.msg = msg;
}
}

主Activity

MainActivity.java：

public class MainActivity extends AppCompatActivity {
private Button button;
private TextView textView;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
button = findViewById(R.id.button);
textView = findViewById(R.id.text);
EventBus.getDefault().register(this);
button.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
TestEvent event = new TestEvent();
event.setMsg("已接收到事件!");
EventBus.getDefault().post(event);
}
});
}
@Subscribe(threadMode = ThreadMode.MAIN)
public void onTestEvent(TestEvent event) {
textView.setText(event.getMsg());
}
@Override
protected void onDestroy() {
EventBus.getDefault().unregister(this);
super.onDestroy();
}
}

运行效果

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三、源码分析

关于观察者模式

• 简介：观察者模式是设计模式中的一种。它是为了定义对象间的一种一对多的依赖关系，即当一个对象的状态发生改变时，所有依赖于它的对象都得到通知并被自动更新。
• 如何使用：这里传送门有相关的demo，这里不再详述。
• 重点：在这个模式中主要包含两个重要的角色：发布者和订阅者（又称观察者）。对应EventBus来说，发布者即发送消息的一方（即调用EventBus.getDefault().post(event)的一方），订阅者即接收消息的一方（即调用EventBus.getDefault().register()的一方）。
  我们已经解决了第一个问题~

关于事件

这里指的事件其实是一个泛泛的统称，指的是一个概念上的东西（当时我还以为一定要以啥Event命名…），通过查阅官方文档，我知道事件的命名格式并没有任何要求，你可以定义一个对象作为事件，也可以发送基本数据类型如int，String等作为一个事件。后续的源码分析我也会再次证明一下。

具体分析

从函数入口开始分析：

1.EventBus#getDefault()：

public static EventBus getDefault() {
if (defaultInstance == null) {
synchronized (EventBus.class) {
if (defaultInstance == null) {
defaultInstance = new EventBus();
}
}
}
return defaultInstance;
}

这里就是采用双重校验并加锁的单例模式生成EventBus实例。

public void register(Object subscriber) {
Class<?> subscriberClass = subscriber.getClass();
List<SubscriberMethod> subscriberMethods = subscriberMethodFinder.findSubscriberMethods(subscriberClass);
synchronized (this) {
for (SubscriberMethod subscriberMethod : subscriberMethods) {
subscribe(subscriber, subscriberMethod);
}
}
}

由于我们传入的为this，即MainActivity的实例，所以第一行代码获取了订阅者的class对象，然后会找出所有订阅的方法。我们看一下第二行的逻辑。

SubscriberMethodFinder#findSubscriberMethods()：

List<SubscriberMethod> findSubscriberMethods(Class<?> subscriberClass) {
List<SubscriberMethod> subscriberMethods = METHOD_CACHE.get(subscriberClass);
if (subscriberMethods != null) {
return subscriberMethods;
}
if (ignoreGeneratedIndex) {
subscriberMethods = findUsingReflection(subscriberClass);
} else {
subscriberMethods = findUsingInfo(subscriberClass);
}
if (subscriberMethods.isEmpty()) {
throw new EventBusException("Subscriber " + subscriberClass + " and its super classes have no public methods with the @Subscribe annotation");
} else {
METHOD_CACHE.put(subscriberClass, subscriberMethods);
return subscriberMethods;
}
}

分析：

• 如果缓存中有对应class的订阅方法列表，则直接返回，这里我们是第一次创建，所以此时subscriberMethods为空；
• 接下来会有一个参数判断，通过查看前面的创建过程，ignoreGeneratedIndex默认为false，进入else代码块，后面生成subscriberMethods成功的话会加入到缓存中，失败的话会throw异常。

2.SubscriberMethodFinder#findUsingInfo()：

private List<SubscriberMethod> findUsingInfo(Class<?> subscriberClass) {
// 2.1
FindState findState = prepareFindState();
findState.initForSubscriber(subscriberClass);
// 2.2
while (findState.clazz != null) {
findState.subscriberInfo = getSubscriberInfo(findState);
if (findState.subscriberInfo != null) {
SubscriberMethod[] array = findState.subscriberInfo.getSubscriberMethods();
for (SubscriberMethod subscriberMethod: array) {
if (findState.checkAdd(subscriberMethod.method, subscriberMethod.eventType)) {
findState.subscriberMethods.add(subscriberMethod);
}
}
} else {
// 2.3
findUsingReflectionInSingleClass(findState);
}
findState.moveToSuperclass();
}
// 2.4
return getMethodsAndRelease(findState);
}

2.1 SubscriberMethodFinder#prepareFindState()：

private static final FindState[] FIND_STATE_POOL = new FindState[POOL_SIZE];
private FindState prepareFindState() {
synchronized(FIND_STATE_POOL) {
for (int i = 0; i < POOL_SIZE; i++) {
FindState state = FIND_STATE_POOL[i];
if (state != null) {
FIND_STATE_POOL[i] = null;
return state;
}
}
}
return new FindState();
}

这个方法是创建一个新的FindState类，通过两种方法获取，一种是从FIND_STATE_POOL即FindState池中取出可用的FindState，如果没有的话，则通过第二种方式：直接new一个新的FindState对象。

FindState#initForSubscriber()：

static class FindState {
// 省略代码
void initForSubscriber(Class<?> subscriberClass) {
this.subscriberClass = clazz = subscriberClass;
skipSuperClasses = false;
subscriberInfo = null;
}
// 省略代码
}

FindState类是SubscriberMethodFinder的内部类，这个方法主要做一个初始化的工作。

2.2 SubscriberMethodFinder#getSubscriberInfo()：

private SubscriberInfo getSubscriberInfo(FindState findState) {
if (findState.subscriberInfo != null && findState.subscriberInfo.getSuperSubscriberInfo() != null) {
SubscriberInfo superclassInfo = findState.subscriberInfo.getSuperSubscriberInfo();
if (findState.clazz == superclassInfo.getSubscriberClass()) {
return superclassInfo;
}
}
if (subscriberInfoIndexes != null) {
for (SubscriberInfoIndex index: subscriberInfoIndexes) {
SubscriberInfo info = index.getSubscriberInfo(findState.clazz);
if (info != null) {
return info;
}
}
}
return null;
}

这里由于初始化的时候，findState.subscriberInfo和subscriberInfoIndexes为空，所以这里直接返回null，后续我们可以再回到这里看看subscriberInfo有什么作用。

2.3 SubscriberMethodFinder#findUsingReflectionInSingleClass()：

private void findUsingReflectionInSingleClass(FindState findState) {
Method[] methods;
try {
// This is faster than getMethods, especially when subscribers are fat classes like Activities
methods = findState.clazz.getDeclaredMethods();
} catch (Throwable th) {
// Workaround for java.lang.NoClassDefFoundError, see https://github.com/greenrobot/EventBus/issues/149
methods = findState.clazz.getMethods();
findState.skipSuperClasses = true;
}
for (Method method: methods) {
int modifiers = method.getModifiers();
if ((modifiers & Modifier.PUBLIC) != 0 && (modifiers & MODIFIERS_IGNORE) == 0) {
Class<?> [] parameterTypes = method.getParameterTypes();
if (parameterTypes.length == 1) {
Subscribe subscribeAnnotation = method.getAnnotation(Subscribe.class);
if (subscribeAnnotation != null) {
// ！！！
Class<?> eventType = parameterTypes[0];
if (findState.checkAdd(method, eventType)) {
ThreadMode threadMode = subscribeAnnotation.threadMode();
findState.subscriberMethods.add(new SubscriberMethod(method, eventType, threadMode, subscribeAnnotation.priority(), subscribeAnnotation.sticky()));
}
}
} else if (strictMethodVerification && method.isAnnotationPresent(Subscribe.class)) {
String methodName = method.getDeclaringClass().getName() + "." + method.getName();
throw new EventBusException("@Subscribe method " + methodName + "must have exactly 1 parameter but has " + parameterTypes.length);
}
} else if (strictMethodVerification && method.isAnnotationPresent(Subscribe.class)) {
String methodName = method.getDeclaringClass().getName() + "." + method.getName();
throw new EventBusException(methodName + " is a illegal @Subscribe method: must be public, non-static, and non-abstract");
}
}
}

这个方法的逻辑是：通过反射的方式获取订阅者类中的所有声明方法，然后在这些方法里面寻找以@Subscribe作为注解的方法进行处理（！！！部分的代码），先经过一轮检查，看看findState.subscriberMethods是否存在，如果没有的话，将方法名，threadMode，优先级，是否为sticky方法封装为SubscriberMethod对象，添加到subscriberMethods列表中。

什么是sticky event？

sticky event，中文名为粘性事件。普通事件是先注册，然后发送事件才能收到；而粘性事件，在发送事件之后再订阅该事件也能收到。此外，粘性事件会保存在内存中，每次进入都会去内存中查找获取最新的粘性事件，除非你手动解除注册。

在这里我们解决了第二个和第三个问题，方法的命名并没有任何要求，只是加上@Subscribe注解即可！同时事件的命名也没有任何要求！

之后这个while循环会继续检查父类，当然遇到系统相关的类时会自动跳过，以提升性能。

2.4 SubscriberMethodFinder#getMethodsAndRelease

private List<SubscriberMethod> getMethodsAndRelease(FindState findState) {
List<SubscriberMethod> subscriberMethods = new ArrayList<>(findState.subscriberMethods);
findState.recycle();
synchronized(FIND_STATE_POOL) {
for (int i = 0; i < POOL_SIZE; i++) {
if (FIND_STATE_POOL[i] == null) {
FIND_STATE_POOL[i] = findState;
break;
}
}
}
return subscriberMethods;
}

这里将subscriberMethods列表直接返回，同时会把findState做相应处理，存储在FindState池中，方便下一次使用，提高性能。

1. EventBus#subscribe()：返回subscriberMethods之后，register方法的最后会调用subscribe方法：

public void register(Object subscriber) {
Class<?> subscriberClass = subscriber.getClass();
List<SubscriberMethod> subscriberMethods = subscriberMethodFinder.findSubscriberMethods(subscriberClass);
synchronized (this) {
for (SubscriberMethod subscriberMethod : subscriberMethods) {
subscribe(subscriber, subscriberMethod);
}
}
}
private void subscribe(Object subscriber, SubscriberMethod subscriberMethod) {
Class<?> eventType = subscriberMethod.eventType;
Subscription newSubscription = new Subscription(subscriber, subscriberMethod);
CopyOnWriteArrayList<Subscription> subscriptions = subscriptionsByEventType.get(eventType);
if (subscriptions == null) {
subscriptions = new CopyOnWriteArrayList <> ();
subscriptionsByEventType.put(eventType, subscriptions);
} else {
if (subscriptions.contains(newSubscription)) {
throw new EventBusException("Subscriber " + subscriber.getClass() + " already registered to event " + eventType);
}
}
int size = subscriptions.size();
for (int i = 0; i <= size; i++) {
if (i == size || subscriberMethod.priority > subscriptions.get(i).subscriberMethod.priority) {
subscriptions.add(i, newSubscription);
break;
}
}
List<Class<?>> subscribedEvents = typesBySubscriber.get(subscriber);
if (subscribedEvents == null) {
subscribedEvents = new ArrayList<>();
typesBySubscriber.put(subscriber, subscribedEvents);
}
subscribedEvents.add(eventType);
if (subscriberMethod.sticky) {
if (eventInheritance) {
// Existing sticky events of all subclasses of eventType have to be considered.
// Note: Iterating over all events may be inefficient with lots of sticky events,
// thus data structure should be changed to allow a more efficient lookup
// (e.g. an additional map storing sub classes of super classes: Class -> List<Class>).
Set<Map.Entry<Class<?>, Object>> entries = stickyEvents.entrySet();
for (Map.Entry<Class<?>, Object> entry : entries) {
Class<?> candidateEventType = entry.getKey();
if (eventType.isAssignableFrom(candidateEventType)) {
Object stickyEvent = entry.getValue();
checkPostStickyEventToSubscription(newSubscription, stickyEvent);
}
}
} else {
Object stickyEvent = stickyEvents.get(eventType);
checkPostStickyEventToSubscription(newSubscription, stickyEvent);
}
}
}

分析：

• 首先，根据subscriberMethod.eventType（在Demo里面指的是TestEvent），在subscriptionsByEventType去查找一个CopyOnWriteArrayList ，如果没有则创建一个新的CopyOnWriteArrayList；
• 然后将这个CopyOnWriteArrayList放入subscriptionsByEventType中，这里的subscriptionsByEventType是一个Map，key为eventType，value为CopyOnWriteArrayList，这个Map非常重要，后续还会用到它；
• 接下来，就是添加newSubscription，它属于Subscription类，里面包含着subscriber和subscriberMethod等信息，同时这里有一个优先级的判断，说明它是按照优先级添加的。优先级越高，会插到在当前List靠前面的位置；
• typesBySubscriber这个类也是一个Map，key为subscriber，value为subscribedEvents，即所有的eventType列表，这个类我找了一下，发现在EventBus#isRegister()方法中有用到，应该是用来判断这个Subscriber是否已被注册过。然后将当前的eventType添加到subscribedEvents中；
• 最后，判断是否是sticky。如果是sticky事件的话，到最后会调用checkPostStickyEventToSubscription()方法。

这里其实就是将所有含@Subscribe注解的订阅方法最终保存在subscriptionsByEventType中。

1. EventBus#checkPostStickyEventToSubscription()：

   private void checkPostStickyEventToSubscription(Subscription newSubscription, Object stickyEvent) {
   if (stickyEvent != null) {
   // If the subscriber is trying to abort the event, it will fail (event is not tracked in posting state)
   // --> Strange corner case, which we don't take care of here.
   postToSubscription(newSubscription, stickyEvent, isMainThread());
   }
   }

   
   接下来，我们重点看post()和postToSubscription()方法。post事件相当于把事件发送出去，我们看看订阅者是如何接收到事件的。

private void checkPostStickyEventToSubscription(Subscription newSubscription, Object stickyEvent) {
if (stickyEvent != null) {
// If the subscriber is trying to abort the event, it will fail (event is not tracked in posting state)
// --> Strange corner case, which we don't take care of here.
postToSubscription(newSubscription, stickyEvent, isMainThread());
}
}

接下来，我们重点看post()和postToSubscription()方法。post事件相当于把事件发送出去，我们看看订阅者是如何接收到事件的。

1. EventBus#post()：

   /** Posts the given event to the event bus. */
   public void post(Object event) {
   // 5.1
   PostingThreadState postingState = currentPostingThreadState.get();
   List <Object> eventQueue = postingState.eventQueue;
   eventQueue.add(event);
   // 5.2
   if (!postingState.isPosting) {
   postingState.isMainThread = isMainThread();
   postingState.isPosting = true;
   if (postingState.canceled) {
   throw new EventBusException("Internal error. Abort state was not reset");
   }
   try {
   while (!eventQueue.isEmpty()) {
   postSingleEvent(eventQueue.remove(0), postingState);
   }
   } finally {
   postingState.isPosting = false;
   postingState.isMainThread = false;
   }
   }
   }

   
   

5.1 代码段分析

• currentPostingThreadState是一个ThreadLocal类型的，里面存储了PostingThreadState，而PostingThreadState中包含了一个eventQueue和其他一些标志位；
• 然后把传入的event，保存到了当前线程中的一个变量PostingThreadState的eventQueue中。

  private final ThreadLocal <PostingThreadState> currentPostingThreadState = new ThreadLocal <PostingThreadState> () {
  @Override
  protected PostingThreadState initialValue() {
  return new PostingThreadState();
  }
  };
  /** For ThreadLocal, much faster to set (and get multiple values). */
  final static class PostingThreadState {
  final List <Object> eventQueue = new ArrayList<>();
  boolean isPosting;
  boolean isMainThread;
  Subscription subscription;
  Object event;
  boolean canceled;
  }

  
  

5.2 代码段分析

• 这里涉及到两个标志位，第一个是isMainThread，判断是否为UI线程；第二个是isPosting，作用是防止方法多次调用。
• 最后调用到postSingleEvent()方法

1. EventBus#postSingleEvent()：

   private void postSingleEvent(Object event, PostingThreadState postingState) throws Error {
   Class<?> eventClass = event.getClass();
   boolean subscriptionFound = false;
   if (eventInheritance) {
   List<Class<?>> eventTypes = lookupAllEventTypes(eventClass);
   int countTypes = eventTypes.size();
   for (int h = 0; h < countTypes; h++) {
   Class<?> clazz = eventTypes.get(h);
   subscriptionFound |= postSingleEventForEventType(event, postingState, clazz);
   }
   } else {
   subscriptionFound = postSingleEventForEventType(event, postingState, eventClass);
   }
   if (!subscriptionFound) {
   if (logNoSubscriberMessages) {
   logger.log(Level.FINE, "No subscribers registered for event " + eventClass);
   }
   if (sendNoSubscriberEvent && eventClass != NoSubscriberEvent.class &&
   eventClass != SubscriberExceptionEvent.class) {
   post(new NoSubscriberEvent(this, event));
   }
   }
   }
   private boolean postSingleEventForEventType(Object event, PostingThreadState postingState, Class <?> eventClass) {
   CopyOnWriteArrayList <Subscription> subscriptions;
   synchronized(this) {
   subscriptions = subscriptionsByEventType.get(eventClass);
   }
   if (subscriptions != null && !subscriptions.isEmpty()) {
   for (Subscription subscription: subscriptions) {
   postingState.event = event;
   postingState.subscription = subscription;
   boolean aborted = false;
   try {
   postToSubscription(subscription, event, postingState.isMainThread);
   aborted = postingState.canceled;
   } finally {
   postingState.event = null;
   postingState.subscription = null;
   postingState.canceled = false;
   }
   if (aborted) {
   break;
   }
   }
   return true;
   }
   return false;
   }

   
   

• 这里会首先取出Event的class类型，然后有一个标志位eventInheritance判断，默认为true，作用在相关代码注释有说，如果设为true的话，它会拿到Event父类的class类型，设为false，可以在一定程度上提高性能；
• 接下来是lookupAllEventTypes()方法，就是取出Event及其父类和接口的class列表，当然重复取的话会影响性能，所以它也有做一个eventTypesCache的缓存，这样不用都重复调用getClass()方法。
• 然后是postSingleEventForEventType()方法，这里就很清晰了，就是直接根据Event类型从subscriptionsByEventType中取出对应的subscriptions，与之前的代码对应，最后调用postToSubscription()方法。

1. EventBus#postToSubscription()：

   private void postToSubscription(Subscription subscription, Object event, boolean isMainThread) {
   switch (subscription.subscriberMethod.threadMode) {
   case POSTING:
   invokeSubscriber(subscription, event);
   break;
   case MAIN:
   if (isMainThread) {
   invokeSubscriber(subscription, event);
   } else {
   mainThreadPoster.enqueue(subscription, event);
   }
   break;
   case MAIN_ORDERED:
   if (mainThreadPoster != null) {
   mainThreadPoster.enqueue(subscription, event);
   } else {
   // temporary: technically not correct as poster not decoupled from subscriber
   invokeSubscriber(subscription, event);
   }
   break;
   case BACKGROUND:
   if (isMainThread) {
   backgroundPoster.enqueue(subscription, event);
   } else {
   invokeSubscriber(subscription, event);
   }
   break;
   case ASYNC:
   asyncPoster.enqueue(subscription, event);
   break;
   default:
   throw new IllegalStateException("Unknown thread mode: " + subscription.subscriberMethod.threadMode);
   }
   }

   
   

这里会根据threadMode来判断应该在哪个线程中去执行方法：

• POSTING：执行invokeSubscriber()方法，就是直接反射调用；
• MAIN：首先去判断当前是否在UI线程，如果是的话则直接反射调用，否则调用mainThreadPoster#enqueue()，即把当前的方法加入到队列之中，然后通过handler去发送一个消息，在handler的handleMessage中去执行方法。具体逻辑在HandlerPoster.java中；
• MAIN_ORDERED：与上面逻辑类似，顺序执行我们的方法；
• BACKGROUND：判断当前是否在UI线程，如果不是的话直接反射调用，是的话通过backgroundPoster.enqueue()将方法加入到后台的一个队列，最后通过线程池去执行；
• ASYNC：与BACKGROUND的逻辑类似，将任务加入到后台的一个队列，最终由Eventbus中的一个线程池去调用，这里的线程池与BACKGROUND逻辑中的线程池用的是同一个。

补充：BACKGROUND和ASYNC有什么区别呢？
BACKGROUND中的任务是一个接着一个的去调用，而ASYNC则会即时异步运行，具体的可以对比AsyncPoster.java和BackgroundPoster.java两者代码实现的区别。

到这里，我们就解决了第四个问题，事件的发送和接收，主要是通过subscriptionsByEventType这个非常重要的列表，我们将订阅即接收事件的方法存储在这个列表，发布事件的时候在列表中查询出相对应的方法并执行~

注意：

不同点：其实整体思路除了在版本3种使用注解获取事件方法名替代以前的遍历指定类的onEventXX方法名并存入subscriptionsByEventType map里之外并无本质上的变化。

不过他的好处在于你指定注解 @Subscribe(threadMode = ThreadMode.MAIN)等注解去解放强制性的方法名绑定，可以试命名更加方便onEvent()，onEventMainThread()，onEventBackgroundThread()，onEventAsync()

版本2：

List<SubscriberMethod> findSubscriberMethods(Class<?> subscriberClass, String eventMethodName) {  
        String key = subscriberClass.getName() + '.' + eventMethodName;  
        List<SubscriberMethod> subscriberMethods;  
        synchronized (methodCache) {  
            subscriberMethods = methodCache.get(key);  
        }  
        if (subscriberMethods != null) {  
            return subscriberMethods;  
        }  
        subscriberMethods = new ArrayList<SubscriberMethod>();  
        Class<?> clazz = subscriberClass;  
        HashSet<String> eventTypesFound = new HashSet<String>();  
        StringBuilder methodKeyBuilder = new StringBuilder();  
        while (clazz != null) {  
            String name = clazz.getName();  
            if (name.startsWith("java.") || name.startsWith("javax.") || name.startsWith("android.")) {  
                // Skip system classes, this just degrades performance  
                break;  
            }  
  
            // Starting with EventBus 2.2 we enforced methods to be public (might change with annotations again)  
            Method[] methods = clazz.getMethods();  
            for (Method method : methods) {  
                String methodName = method.getName();  
                if (methodName.startsWith(eventMethodName)) {  
                    int modifiers = method.getModifiers();  
                    if ((modifiers & Modifier.PUBLIC) != 0 && (modifiers & MODIFIERS_IGNORE) == 0) {  
                        Class<?>[] parameterTypes = method.getParameterTypes();  
                        if (parameterTypes.length == 1) {  
                            String modifierString = methodName.substring(eventMethodName.length());  
                            ThreadMode threadMode;  
                            if (modifierString.length() == 0) {  
                                threadMode = ThreadMode.PostThread;  
                            } else if (modifierString.equals("MainThread")) {  
                                threadMode = ThreadMode.MainThread;  
                            } else if (modifierString.equals("BackgroundThread")) {  
                                threadMode = ThreadMode.BackgroundThread;  
                            } else if (modifierString.equals("Async")) {  
                                threadMode = ThreadMode.Async;  
                            } else {  
                                if (skipMethodVerificationForClasses.containsKey(clazz)) {  
                                    continue;  
                                } else {  
                                    throw new EventBusException("Illegal onEvent method, check for typos: " + method);  
                                }  
                            }  
                            Class<?> eventType = parameterTypes[0];  
                            methodKeyBuilder.setLength(0);  
                            methodKeyBuilder.append(methodName);  
                            methodKeyBuilder.append('>').append(eventType.getName());  
                            String methodKey = methodKeyBuilder.toString();  
                            if (eventTypesFound.add(methodKey)) {  
                                // Only add if not already found in a sub class  
                                subscriberMethods.add(new SubscriberMethod(method, threadMode, eventType));  
                            }  
                        }  
                    } else if (!skipMethodVerificationForClasses.containsKey(clazz)) {  
                        Log.d(EventBus.TAG, "Skipping method (not public, static or abstract): " + clazz + "."  
                                + methodName);  
                    }  
                }  
            }  
            clazz = clazz.getSuperclass();  
        }  
        if (subscriberMethods.isEmpty()) {  
            throw new EventBusException("Subscriber " + subscriberClass + " has no public methods called "  
                    + eventMethodName);  
        } else {  
            synchronized (methodCache) {  
                methodCache.put(key, subscriberMethods);  
            }  
            return subscriberMethods;  
        }  
    }  

版本3：

private void findUsingReflectionInSingleClass(FindState findState) {
    Method[] methods;
    try {
        // This is faster than getMethods, especially when subscribers are fat classes like Activities
        methods = findState.clazz.getDeclaredMethods();
    } catch (Throwable th) {
        // Workaround for java.lang.NoClassDefFoundError, see https://github.com/greenrobot/EventBus/issues/149
        methods = findState.clazz.getMethods();
        findState.skipSuperClasses = true;
    }
    for (Method method: methods) {
        int modifiers = method.getModifiers();
        if ((modifiers & Modifier.PUBLIC) != 0 && (modifiers & MODIFIERS_IGNORE) == 0) {
            Class<?> [] parameterTypes = method.getParameterTypes();
            if (parameterTypes.length == 1) {
                Subscribe subscribeAnnotation = method.getAnnotation(Subscribe.class);
                if (subscribeAnnotation != null) {
                    // ！！！
                    Class<?> eventType = parameterTypes[0];
                    if (findState.checkAdd(method, eventType)) {
                        ThreadMode threadMode = subscribeAnnotation.threadMode();
                        findState.subscriberMethods.add(new SubscriberMethod(method, eventType, threadMode, subscribeAnnotation.priority(), subscribeAnnotation.sticky()));
                    }
                }
            } else if (strictMethodVerification && method.isAnnotationPresent(Subscribe.class)) {
                String methodName = method.getDeclaringClass().getName() + "." + method.getName();
                throw new EventBusException("@Subscribe method " + methodName + "must have exactly 1 parameter but has " + parameterTypes.length);
            }
        } else if (strictMethodVerification && method.isAnnotationPresent(Subscribe.class)) {
            String methodName = method.getDeclaringClass().getName() + "." + method.getName();
            throw new EventBusException(methodName + " is a illegal @Subscribe method: must be public, non-static, and non-abstract");
        }
    }
}

其次的不同点，加入了状态标识和一些缓存处理，使得逻辑和性能都有一定的优化……