如果熟悉C#語言的小夥伴們一般都會知道委託、事件的好處,只需在某個類中提前定義好公開的委託或事件(委託的特殊表現形式)變數,然後在其它類中就可以很隨意的訂閱該委託或事件,當委託或事件被觸發執行時,會自動通知所有的訂閱者進行消費處理。(觀察者模式用委託來實現是最好不過了,DDD所提倡的事件驅動其根本理念也是如此),當然我這裡想到的是不需要在每個類中進行定義委託或事件,而是由一個統一的中介者(即EventPublishSubscribeUtils)來提供事件的訂閱及釋出操作,這樣各模組之間無需直接依賴,只需通過中介者完成釋出通知與訂閱回撥即可,何樂而不為呢?
這裡我先借助C#語言獨有的委託型別快速實現了一個簡易的EventPublishSubscribeUtils,程式碼如下:
/// <summary>
/// 自定義事件釋出訂閱回撥工具類(業務解藕、關注點分離,避免互相依賴)--演示版
/// EventBus簡化版,觀察者模式
/// author:zuowenjun
/// </summary>
public static class EventPublishSubscribeUtils
{
private static ConcurrentDictionary<Type, EventHandler<object>> EventHandlers { get; } = new ConcurrentDictionary<Type, EventHandler<object>>();
private static void removeRegisters(ref EventHandler<object> srcEvents, EventHandler<object> removeTargetEvents)
{
var evtTypes = removeTargetEvents.GetInvocationList().Select(d => d.GetType());
var registeredEventHandlers = Delegate.Combine(srcEvents.GetInvocationList().Where(ei => evtTypes.Contains(ei.GetType())).ToArray());
srcEvents -= (EventHandler<object>)registeredEventHandlers;
}
public static void Register<T>(EventHandler<object> eventHandlers)
{
EventHandlers.AddOrUpdate(typeof(T), eventHandlers,
(t, e) =>
{
//先根據訂閱委託型別匹匹配過濾掉之前已有的相同訂閱,然後再重新訂閱,防止重複訂閱,多次執行的情況。
removeRegisters(ref e, eventHandlers);
e += eventHandlers;
return e;
});
}
public static void UnRegister<T>(EventHandler<object> eventHandlers = null)
{
Type eventMsgType = typeof(T);
if (eventHandlers == null)
{
EventHandlers.TryRemove(eventMsgType, out eventHandlers);
return;
}
var e = EventHandlers[eventMsgType];
removeRegisters(ref e, eventHandlers);
}
public static void PublishEvent<T>(T eventMsg, object sender)
{
Type eventMsgType = eventMsg.GetType();
if (EventHandlers.ContainsKey(eventMsgType))
{
EventHandlers[eventMsgType].Invoke(sender, eventMsg);
}
}
}
然後使用就比較簡單了,我們只需通過EventPublishSubscribeUtils.Register註冊訂閱事件訊息,通過EventPublishSubscribeUtils.PublishEvent釋出事件通知,這樣就可以讓兩個甚至多個不相關的模組(類)能夠通過訊息型別實現1對多的通訊與協同處理。使用示例程式碼如下:
class EventMessage
{
public string Name { get; set; }
public string Msg { get; set; }
public DateTime CreatedDate { get; set; }
}
class DemoA
{
public DemoA()
{
EventHandler<object> eventHandlers = EventCallback1;
eventHandlers += EventCallback2;
EventPublishSubscribeUtils.Register<EventMessage>(eventHandlers);
}
private void EventCallback1(object sender, object e)
{
string json = JsonConvert.SerializeObject(e);
System.Diagnostics.Debug.WriteLine($"EventCallback1=> sender:{sender},e:{json}");
}
private void EventCallback2(object sender, object e)
{
string json = JsonConvert.SerializeObject(e);
System.Diagnostics.Debug.WriteLine($"EventCallback2=> sender:{sender},e:{json}");
}
}
class DemoB
{
public void ShowMsg(string name, string msg)
{
System.Diagnostics.Debug.WriteLine($"ShowMsg=> name:{name},msg:{msg}");
var eventMsg = new EventMessage
{
Name = name,
Msg = msg,
CreatedDate = DateTime.Now
};
EventPublishSubscribeUtils.PublishEvent(eventMsg, nameof(DemoB.ShowMsg));
}
}
//main方法中使用:
var demoA = new DemoA();
var demoB = new DemoB();
demoB.ShowMsg("夢在旅途", "i love csharp and java!");
從上述示例程式碼中可以看出,DemoA與DemoB各為獨立,互不依賴,它們都不知道有對方的存在,它們只關心業務的處理,通過執行demoB.ShowMsg方法進而觸發回撥demoA.EventCallback1,demoA.EventCallback2方法,是不是比起直接從DemoA中調DemoB更好呢?
c#有委託型別(方法的引用),那如果是在java中該如何實現呢?
其實同理,我們可以藉助匿名內部類+匿名實現類的方式(如:函式式介面)實現與C#異曲同工的效果,同樣可以實現類似的事件釋出與訂閱功能,如下便是採用java語言的實現EventPublishSubscribeUtils類的程式碼:
這個因專案需要,我特意實現了兩種模式,一種支援1對多的普通方式,另一種支援1對1的訂閱回撥方式,有返回值。
/**
* 自定義事件釋出訂閱回撥工具類(業務解藕、關注點分離,避免互相依賴)
* EventBus簡化版,觀察者模式
* <pre>
* 支援兩種模式
* 1.無返回值:訂閱事件消費(register)+ 釋出事件訊息(publishEvent/publishEventAsync)
* 2.有返回值:監聽回撥通知處理(listenCallback)+通知回撥(notifyCallback),通過notifyMessageType+MessageChannel 即可標識唯一的一組通知回撥與監聽回撥處理
* <pre>
* @author zuowenjun
* @date 20200310
*/
public final class EventPublishSubscribeUtils {
private static final Logger LOGGER = LoggerFactory.getLogger(EventPublishSubscribeUtils.class);
private static final Map<Class<?>, LinkedList<Consumer<Object>>> eventConsumers = new ConcurrentHashMap<>();
private static final Map<Class<?>, ConcurrentHashMap<MessageChannel, Function<Object, Object>>> callbackFuncs = new ConcurrentHashMap<>();
private EventPublishSubscribeUtils() {
}
/**
* 註冊事件回撥消費者
* 用法:EventSubscribeConsumeUtils.register(this::xxxx方法) 或lambda表示式
* 注意:若回撥方法新增了事務註解,則應指派其代理物件的方法來完成回撥,如:
* EventSubscribeConsumeUtils.register((xxxService)SpringUtils.getBean(this.class)::xxxx方法)
*
* @param eventConsumer
*/
public static void register(Class<?> eventMessageType, Consumer<Object> eventConsumer) {
if (eventConsumer == null) {
return;
}
LinkedList<Consumer<Object>> eventConsumerItems = null;
if (!eventConsumers.containsKey(eventMessageType)) {
eventConsumers.putIfAbsent(eventMessageType, new LinkedList<>());
}
eventConsumerItems = eventConsumers.get(eventMessageType);
eventConsumerItems.add(eventConsumer);
}
/**
* 取消訂閱回撥
*
* @param eventMessageType
* @param eventConsumer
*/
public static void unRegister(Class<?> eventMessageType, Consumer<Object> eventConsumer) {
if (!eventConsumers.containsKey(eventMessageType)) {
return;
}
LinkedList<Consumer<Object>> eventConsumerItems = eventConsumers.get(eventMessageType);
int eventConsumerIndex = eventConsumerItems.indexOf(eventConsumer);
if (eventConsumerIndex == -1) {
return;
}
eventConsumerItems.remove(eventConsumerIndex);
}
/**
* 釋出事件,同步觸發執行回撥事件消費者方法(存在阻塞等待),即事件訊息生產者
* 用法:在需要觸發事件訊息回撥時呼叫,如:publishEvent(eventMessage);
*
* @param eventMessage
*/
public static <T> void publishEvent(T eventMessage) {
Class<?> eventMessageType = eventMessage.getClass();
if (!eventConsumers.containsKey(eventMessageType)) {
return;
}
LOGGER.info("事件已釋出,正在執行通知消費:{}", JSONObject.toJSONString(eventMessage));
for (Consumer<Object> eventConsumer : eventConsumers.get(eventMessageType)) {
try {
eventConsumer.accept(eventMessage);
} catch (Exception ex) {
LOGGER.error("eventConsumer.accept error:{},eventMessageType:{},eventMessage:{}",
ex, eventMessageType, JSONObject.toJSONString(eventMessage));
}
}
}
/**
* 釋出事件,非同步觸發執行回撥事件消費者方法(非同步非阻塞),即事件訊息生產者
* 用法:在需要觸發事件訊息回撥時呼叫,如:publishEventAsync(eventMessage);
*
* @param eventMessage
*/
public static <T> void publishEventAsync(final T eventMessage) {
Executor asyncTaskExecutor = (Executor) SpringUtils.getBean("asyncTaskExecutor");
asyncTaskExecutor.execute(() -> {
publishEvent(eventMessage);
});
}
/**
* 監聽回撥處理(需要有返回值),即有返回值的回撥消費者
*
* @param notifyMessageType
* @param messageChannel
* @param callbackFunc
*/
public static void listenCallback(Class<?> notifyMessageType, MessageChannel messageChannel, Function<Object, Object> callbackFunc) {
if (!callbackFuncs.containsKey(notifyMessageType)) {
callbackFuncs.putIfAbsent(notifyMessageType, new ConcurrentHashMap<>());
}
Map<MessageChannel, Function<Object, Object>> functionMap = callbackFuncs.get(notifyMessageType);
if (!functionMap.containsKey(messageChannel)) {
functionMap.putIfAbsent(messageChannel, callbackFunc);
} else {
LOGGER.error("該通知訊息型別:{}+訊息通道:{},已被訂閱監聽,重複訂閱監聽無效!", notifyMessageType.getSimpleName(), messageChannel.getDescription());
}
}
/**
* 通知回撥(同步等待獲取監聽回撥的處理結果),即生產者
*
* @param notifyMessage
* @param messageChannel
* @param <R>
* @return
*/
@SuppressWarnings("unchecked")
public static <R> R notifyCallback(Object notifyMessage, MessageChannel messageChannel) {
Class<?> notifyMessageType = notifyMessage.getClass();
Map<MessageChannel, Function<Object, Object>> functionMap = callbackFuncs.getOrDefault(notifyMessageType, null);
if (functionMap != null) {
Function<Object, Object> callbackFunction = functionMap.getOrDefault(messageChannel, null);
if (callbackFunction != null) {
LOGGER.info("通知回撥訊息已釋出,正在執行回撥處理:{},messageChannel:[{}]", JSONObject.toJSONString(notifyMessage), messageChannel.getDescription());
Object result = callbackFunction.apply(notifyMessage);
try {
return (R) result;
} catch (ClassCastException castEx) {
throw new ClassCastException(String.format("監聽回撥處理後返回值實際型別與釋出通知回撥待接收的值預期型別不一致,導致型別轉換失敗:%s," +
"請確保notifyCallback與listenCallback針對通知訊息型別:%s+訊息通道:%s返回值型別必需一致。",
castEx.getMessage(), notifyMessageType.getSimpleName(), messageChannel.getDescription()));
}
}
}
return null;
}
}
當然如果需要實現1對1的通訊,除了指定訊息型別外,還需要指定訊息通訊通道(即:唯一標識),目的是可以實現同一種訊息型別,支援不同的點對點的處理。
/**
* 自定義訊息通道
* 作用:用於識別同一個訊息型別下不同的監聽回撥者(notifyMessage+messageChannel 即可標識唯一的一組通知回撥[生產者]與監聽回撥[消費者])
* @author zuowenjun
* @date 2020-03-31
*/
public enum MessageChannel {
None("無效"),
MSG_A("測試訊息A"),
;
private String description;
MessageChannel(String description) {
this.description=description;
}
public String getDescription() {
return description;
}
}
使用方法示例程式碼如下:
@Service
public class DemoAService {
private static final Logger LOGGER = LoggerFactory.getLogger(DemoAService.class);
public void showMsg(String name, String msg) {
System.out.printf("【%1$tF %1$tT.%1$tL】hello!%s,DemoAService showMsg:%s %n", new Date(), name, msg);
EventMessage eventMessage = new EventMessage();
eventMessage.setName("aaa");
eventMessage.setMsg("test");
eventMessage.setCreatedDate(new Date());
EventPublishSubscribeUtils.publishEvent(eventMessage);
String msgJsonStr = EventPublishSubscribeUtils.notifyCallback(eventMessage, MessageChannel.MSG_A);
System.out.printf("【%1$tF %1$tT.%1$tL】DemoAService showMsg notifyCallback json result:%2$s %n", new Date(), msgJsonStr);
}
}
@Service
public class DemoBService {
@Autowired
private DemoAService demoAService;
@PostConstruct
public void init(){
//訂閱消費,無返回值,支援1對多,即:同一個訊息型別可同時被多個消費者訂閱
EventPublishSubscribeUtils.register(EventMessage.class,this::showFinishedMsg);
//訂閱監聽回撥,有返回值,只能1對1
EventPublishSubscribeUtils.listenCallback(EventMessage.class, MessageChannel.MSG_A,this::getMsgCallbak);
}
private void showFinishedMsg(Object eventMsg){
EventMessage eventMessage=(EventMessage)eventMsg;
System.out.printf("【%1$tF %1$tT.%1$tL】%s,receive msg:%s doing...%n",
eventMessage.getCreatedDate(),eventMessage.getName(),eventMessage.getMsg());
//模擬邏輯處理
try {
Thread.sleep(500L);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.printf("【%1$tF %1$tT.%1$tL】%s,do finished!!!%n",new Date(),eventMessage.getName());
}
private String getMsgCallbak(Object eventMsg){
EventMessage eventMessage=(EventMessage)eventMsg;
eventMessage.setMsg(eventMessage.getMsg()+"--callback added!");
eventMessage.setCreatedDate(new Date());
System.out.printf("【%1$tF %1$tT.%1$tL】%s,do msg callback!!!%n",new Date(),eventMessage.getName());
return JSONObject.toJSONString(eventMessage);
}
}
如上程式碼所示,我們藉助於EventPublishSubscribeUtils,解耦了兩個Service Bean之間的依賴,避免了迴圈依賴的問題,去掉了之前為了解決迴圈依賴而使用@Lazy註解的方式,更易於擴充套件與更改。其實Spring底層也使用了類似的Event機制,說明這種方式還是有合適的用武之地的。
這裡我通過簡單的關係圖來對比未引用EventPublishSubscribeUtils前與引用後的區別,大家可以感受一下哪種更方便:
之前:
之後:
最後,關於業務解耦,分清業務邊界,我個人認為跨程式通訊使用MQ,同程式跨多模組(類,或者說跨多業務邊界)可使用Event事件驅動思路來解決。大家覺得如何呢?如果有更好的方案歡迎評論交流,謝謝。