谷歌建议框架 EventBus 理解源码

写这个建议框架为了便于观察者模式：

一 ，实现第一个类
import com.google.common.base.Preconditions;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
/**
* 观察者综合类
*/
public class ObserverAction {
private Object target;//表示观察者的类
private Method method;//表示方法
public ObserverAction(Object target, Method method) {
this.target = Preconditions.checkNotNull(target);
this.method = method;
this.method.setAccessible(true);
}
public void execute(Object event) {
try {
method.invoke(target, event);
} catch (InvocationTargetException | IllegalAccessException e) {
e.printStackTrace();
}
}
}

二 ，实现第二个类

import com.google.common.base.Preconditions;
import java.lang.reflect.Method;
import java.util.*;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;
import java.util.concurrent.CopyOnWriteArraySet;
/**
* Event Bus 注册表类
*/
public class ObserverRegistry {
private static ConcurrentMap<Class<?>, CopyOnWriteArraySet<ObserverAction>> registry = new ConcurrentHashMap<>();
/**
* 把它导入到另一个map里边 用的 CopyOnWriteArraySet 这样在复制完成之后在替换
* 避免冲突
* @param observer
*/
public void register(Object observer) {
Map<Class<?>, Collection<ObserverAction>> observerActions = findAllObserverActions(observer);
for (Map.Entry<Class<?>, Collection<ObserverAction>> entry : observerActions.entrySet()) {
Class<?> eventType = entry.getKey();
Collection<ObserverAction> eventActions = entry.getValue();
CopyOnWriteArraySet<ObserverAction> registeredEventActions = registry.get(eventType);
if(registeredEventActions==null){
registry.put(eventType, new CopyOnWriteArraySet<>());
registeredEventActions=registry.get(eventType);
}
registeredEventActions.addAll(eventActions);
}
}
private Map<Class<?>, Collection<ObserverAction>> findAllObserverActions(Object observer) {
Map<Class<?>, Collection<ObserverAction>> observerActions = new HashMap<>();
Class<?> clazz = observer.getClass();
for (Method method : getAnnotatedMethods(clazz)) {
Class<?>[] parameterTypes = method.getParameterTypes();
Class<?> eventType = parameterTypes[0];
if (!observerActions.containsKey(eventType)) {//不存在这种类型,也即是说一个类里边要存在不同值的参数类型才可以
observerActions.put(eventType, new ArrayList<>());
}
observerActions.get(eventType).add(new ObserverAction(observer, method));
}
return observerActions;
}
/**
* 筛选出方法中带有@Subscribe标签的
*
* @param clazz
* @return
*/
private List<Method> getAnnotatedMethods(Class<?> clazz) {
List<Method> annotatedMethods = new ArrayList<>();
for (Method method : clazz.getDeclaredMethods()) {//获取所有public方法
if (method.isAnnotationPresent(Subscribe.class)) {//如果该方法上有@Subscribe标签
//检查下这个方法中是否有参数
Class<?>[] parameterTypes = method.getParameterTypes();
Preconditions.checkArgument(parameterTypes.length == 1,
"Method %s has @Subscribe annotation but has %s parameters."
+ "Subscriber methods must have exactly 1 parameter.",
method, parameterTypes.length);
annotatedMethods.add(method);
}
}
return annotatedMethods;
}
}

三 ，实现一个标签
import com.google.common.annotations.Beta;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.METHOD)
@Beta
public @interface Subscribe {
}

四 ，实现测试类
package com.jxd.bus;
public class Test {
@Subscribe
public void aaa(String a){
System.out.println("hell world Test"+a);
}
}

五 ，测试结果

public static void main(String[] args) {

Test t =new Test(); new ObserverRegistry().register(t);

System.out.println(registry.size());

Iterator<ObserverAction> a=registry.get(String.class).iterator();

a.next().execute("  Event BUS ");

}

打印结果

hell world Test  Event BUS

最后

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