差異處

這裏顯示兩個版本的差異處。

--- java:guava:eventbusbasicusage [2020/10/25 23:09]
tony [How to?]
+++ java:guava:eventbusbasicusage [2023/06/25 09:48]
@@ 行 1: / 行 1: @@
-{{tag>java guava}}
-====== EventBus Basic Usage ======
-===== Introduction =====
-最近在看Domain Event的實作方式，剛好看到Teddy分享使用Guava的EventBus來處理事件的註冊與分派，於是花了一些時間實驗API的用法。以下內容分享給大家。Source code可以從[[https://github.com/frank007love/GuavaEventBusPractice|link]]下載。
-===== How to? =====
-==== Event ====
-我的範例事件為MJGotGodGuyCardEvent:
-<code java>
-public class MJGotGodGuyCardEvent {
-    private final String girlName;
-    public MJGotGodGuyCardEvent(String girlName) {
-        this.girlName = girlName;
-    }
-    public String getGirlName() {
-        return girlName;
-    }
-}
-</code>
-==== Event Handler ====
-我的事件處理者有兩個，第一個為MJGoToPronhub。需注意的是:
-  * @Subscribe: 用以宣告處理函式，函式只允許一個參數，且要與Event物件相同。
-  * @AllowConcurrentEvents: 用以告知EventBus此函式可以接受Concurrent存取，預設會使用循序方式存取此函式。
-<code java>
-public class MJGoToPronhub {
-    private static Logger logger = LoggerFactory.getLogger(MJGoToPronhub.class);
-    private List<MJGotGodGuyCardEvent> receivedEvents = new CopyOnWriteArrayList<>();
-    @AllowConcurrentEvents
-    @Subscribe
-    public void handle(MJGotGodGuyCardEvent event) {
-        receivedEvents.add(event);
-        logger.info("MJGoToPronhub due to {}", event.getGirlName());
-    }
-    public List<MJGotGodGuyCardEvent> getReceivedEvents(){
-        return receivedEvents;
-    }
-}
-</code>
-另外一個實作內容類似，不做贅述，名稱為MJGoToWanhua。
-==== EventBus ====
-用法相當簡單，只要透過EventBus的register把處理物件進去後，在負責發送通知的client使用post即可"循序"的讓handler處理訊息:
-<code java>
-public class TestEventBus {
-    private EventBus eventBus = new EventBus();
-    private MJGoToPronhub MJGoToPronhubHandler = new MJGoToPronhub();
-    private MJGoToWanhua MJGoToWanhuaHandler = new MJGoToWanhua();
-    private void thenTheHandlerShouldReceiveTheEvent() {
-        assertEquals(1, MJGoToPronhubHandler.getReceivedEvents().size());
-        assertEquals(1, MJGoToWanhuaHandler.getReceivedEvents().size());
-    }
-    private void givenEventBusRegisterTwoGoodHandler(EventBus eventBus) {
-        eventBus.register(MJGoToPronhubHandler);
-        eventBus.register(MJGoToWanhuaHandler);
-    }
-    @Test
-    public void ShouldGetReceivedEventsWhenPostEventToHandlers() {
-        givenEventBusRegisterTwoGoodHandler(eventBus);
-        MJGotGodGuyCardEvent event = new MJGotGodGuyCardEvent("Nancy");
-        eventBus.post(event);
-        thenTheHandlerShouldReceiveTheEvent();
-    }
-}
-</code>
-==== AsyncEventBus ====
-假如覺得循序處理太慢，可以使用AsyncEventBus，使用方法與EventBus相同，但它post是non-blocking的:
-<code java>
-public class TestAsyncEventBus {
-    private AsyncEventBus asyncEventBus = new AsyncEventBus(Executors.newCachedThreadPool());
-    private MJGoToPronhub MJGoToPronhubHandler = new MJGoToPronhub();
-    private MJGoToWanhua MJGoToWanhuaHandler = new MJGoToWanhua();
-    private void thenTheHandlerShouldReceiveTheEvent() {
-        assertEquals(1, MJGoToPronhubHandler.getReceivedEvents().size());
-        assertEquals(1, MJGoToWanhuaHandler.getReceivedEvents().size());
-    }
-    private void givenEventBusRegisterTwoGoodHandler(EventBus eventBus) {
-        eventBus.register(MJGoToPronhubHandler);
-        eventBus.register(MJGoToWanhuaHandler);
-    }
-    private MJGotGodGuyCardEvent givenDelayedMJGotGodGuyCardEvent(CountDownLatch latch) {
-        return new MJGotGodGuyCardEvent("Nancy") {
-            @Override
-            public String getGirlName() {
-                try {
-                    TimeUnit.SECONDS.sleep(1);
-                    return super.getGirlName();
-                } catch (InterruptedException e) {
-                    throw new RuntimeException(e);
-                } finally {
-                    latch.countDown();
-                }
-            }
-        };
-    }
-    private void thenPostShouldBeNotBlocked(long startTime) {
-        long afterTime = System.currentTimeMillis();
-        assertTrue((afterTime-startTime)<1000);
-    }
-    private void thenPostShouldBeDoneWithParallel(long startTime, CountDownLatch latch) throws InterruptedException {
-        latch.await();
-        long afterTime = System.currentTimeMillis();
-        assertTrue((afterTime-startTime)>1000);
-    }
-    @Test
-    public void testAsyncEventBus() throws InterruptedException {
-        givenEventBusRegisterTwoGoodHandler(asyncEventBus);
-        CountDownLatch latch = new CountDownLatch(2);
-        MJGotGodGuyCardEvent event = givenDelayedMJGotGodGuyCardEvent(latch);
-        long startTime = System.currentTimeMillis();
-        asyncEventBus.post(event);
-        thenPostShouldBeNotBlocked(startTime);
-        thenPostShouldBeDoneWithParallel(startTime, latch);
-        thenTheHandlerShouldReceiveTheEvent();
-    }
-}
-</code>
-==== Notes ====
-  * 預設情況下，Handler處理發生例外時，並不影響工作繼續進行。
-  * 可以透過實做SubscriberExceptionHandler去達到自己的例外處理需求，可由constructor去注入。
-===== Reference =====
-  * [[http://teddy-chen-tw.blogspot.com/2019/12/blog-post_26.html|領域事件的發送與接收（上）]]
-  * [[http://teddy-chen-tw.blogspot.com/2019/12/blog-post_27.html|領域事件的發送與接收（下）]]
-=====  =====
-----
-\\
-~~DISQUS~~