在Google Guava 10版本引入了EventBus, 它主要用來(lái)簡(jiǎn)化我們處理生產(chǎn)/消費(fèi)者編程模型.?
基本用法
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使用Guava之后, 如果要訂閱消息, 就不用再繼承指定的接口, 只需要在指定的方法上加上@Subscribe注解即可:?
- public ? class ?EventListener?{??
- ???
- ???? public ? int ?lastMessage?=? 0 ;??
- ???
- ???? @Subscribe ??
- ???? public ? void ?listen(OurTestEvent?event)?{??
- ????????lastMessage?=?event.getMessage();??
- ????}??
- ???
- ???? public ? int ?getLastMessage()?{??
- ???????? return ?lastMessage;??
- ????}??
- }??
上面的lastMessage用來(lái)接收消息.?
下面定義的類用來(lái)對(duì)消息進(jìn)行封裝:?
- public ? class ?OurTestEvent?{??
- ???
- ???? private ? final ? int ?message;??
- ???
- ???? public ?OurTestEvent( int ?message)?{??
- ???????? this .message?=?message;??
- ????}??
- ???
- ???? public ? int ?getMessage()?{??
- ???????? return ?message;??
- ????}??
- }??
通過(guò)寫一個(gè)測(cè)試來(lái)了解EventBus如何工作:?
- @Test ??
- public ? void ?shouldReceiveEvent()? throws ?Exception?{??
- ???
- ???? //?given ??
- ????EventBus?eventBus?=? new ?EventBus( "test" );??
- ????EventListener?listener?=? new ?EventListener();??
- ???
- ????eventBus.register(listener);??
- ???
- ???? //?when ??
- ????eventBus.post( new ?OurTestEvent( 200 ));??
- ???
- ???? //?then ??
- ????assertThat(listener.getLastMessage()).isEqualTo( 200 );??
- }??
上面的測(cè)試是不是很簡(jiǎn)單??
MultiListener的使用
?
只需要在要訂閱消息的方法上加上@Subscribe注解即可實(shí)現(xiàn)對(duì)多個(gè)消息的訂閱:?
- public ? class ?MultipleListener?{??
- ???
- ???? public ?Integer?lastInteger;??
- ???? public ?Long?lastLong;??
- ???
- ???? @Subscribe ??
- ???? public ? void ?listenInteger(Integer?event)?{??
- ????????lastInteger?=?event;??
- ????}??
- ???
- ???? @Subscribe ??
- ???? public ? void ?listenLong(Long?event)?{??
- ????????lastLong?=?event;??
- ????}??
- ???
- ???? public ?Integer?getLastInteger()?{??
- ???????? return ?lastInteger;??
- ????}??
- ???
- ???? public ?Long?getLastLong()?{??
- ???????? return ?lastLong;??
- ????}??
- }??
下面是對(duì)應(yīng)的測(cè)試:?
- @Test ??
- public ? void ?shouldReceiveMultipleEvents()? throws ?Exception?{??
- ???
- ???? //?given ??
- ????EventBus?eventBus?=? new ?EventBus( "test" );??
- ????MultipleListener?multiListener?=? new ?MultipleListener();??
- ???
- ????eventBus.register(multiListener);??
- ???
- ???? //?when ??
- ????eventBus.post( new ?Integer( 100 ));??
- ????eventBus.post( new ?Long( 800 ));??
- ???
- ???? //?then ??
- ????assertThat(multiListener.getLastInteger()).isEqualTo( 100 );??
- ????assertThat(multiListener.getLastLong()).isEqualTo(800L);??
- }??
高級(jí)用法
?
1.Dead Event
?
如果EventBus發(fā)送的消息都不是訂閱者關(guān)心的稱之為Dead Event. 看下面的例子:?
- /** ?
- ?*?Listener?waiting?for?the?event?that?any?message?was?posted?but?not?delivered?to?anyone ?
- ?*/ ??
- public ? class ?DeadEventListener?{??
- ???
- ???? boolean ?notDelivered?=? false ;??
- ???
- ???? @Subscribe ??
- ???? public ? void ?listen(DeadEvent?event)?{??
- ????????notDelivered?=? true ;??
- ????}??
- ???
- ???? public ? boolean ?isNotDelivered()?{??
- ???????? return ?notDelivered;??
- ????}??
- }??
下面是測(cè)試類:?
- @Test ??
- public ? void ?shouldDetectEventWithoutListeners()? throws ?Exception?{??
- ???
- ???? //?given ??
- ????EventBus?eventBus?=? new ?EventBus( "test" );??
- ???
- ????DeadEventListener?deadEventListener?=? new ?DeadEventListener();??
- ????eventBus.register(deadEventListener);??
- ???
- ???? //?when ??
- ????eventBus.post( new ?OurTestEvent( 200 ));??
- ???
- ????assertThat(deadEventListener.isNotDelivered()).isTrue();??
- }??
如果沒(méi)有消息訂閱者監(jiān)聽(tīng)消息, EventBus將發(fā)送DeadEvent消息, 這時(shí)我們可以通過(guò)log的方式來(lái)記錄這種狀態(tài).?
2.Event的繼承
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如果Listener A監(jiān)聽(tīng)Event A, 而Event A有一個(gè)子類Event B, 此時(shí)Listener A將同時(shí)接收Event A和B消息?
看下面的例子:?
- public ? class ?NumberListener?{??
- ???
- ???? private ?Number?lastMessage;??
- ???
- ???? @Subscribe ??
- ???? public ? void ?listen(Number?integer)?{??
- ????????lastMessage?=?integer;??
- ????}??
- ???
- ???? public ?Number?getLastMessage()?{??
- ???????? return ?lastMessage;??
- ????}??
- }??
- ??
- ??????
- public ? class ?IntegerListener?{??
- ???
- ???? private ?Integer?lastMessage;??
- ???
- ???? @Subscribe ??
- ???? public ? void ?listen(Integer?integer)?{??
- ????????lastMessage?=?integer;??
- ????}??
- ???
- ???? public ?Integer?getLastMessage()?{??
- ???????? return ?lastMessage;??
- ????}??
- }??
對(duì)應(yīng)的測(cè)試類:?
- @Test ??
- public ? void ?shouldGetEventsFromSubclass()? throws ?Exception?{??
- ???
- ???? //?given ??
- ????EventBus?eventBus?=? new ?EventBus( "test" );??
- ????IntegerListener?integerListener?=? new ?IntegerListener();??
- ????NumberListener?numberListener?=? new ?NumberListener();??
- ????eventBus.register(integerListener);??
- ????eventBus.register(numberListener);??
- ???
- ???? //?when ??
- ????eventBus.post( new ?Integer( 100 ));??
- ???
- ???? //?then ??
- ????assertThat(integerListener.getLastMessage()).isEqualTo( 100 );??
- ????assertThat(numberListener.getLastMessage()).isEqualTo( 100 );??
- ???
- ???? //when ??
- ????eventBus.post( new ?Long(200L));??
- ???
- ???? //?then ??
- ???? //?this?one?should?has?the?old?value?as?it?listens?only?for?Integers ??
- ????assertThat(integerListener.getLastMessage()).isEqualTo( 100 );??
- ????assertThat(numberListener.getLastMessage()).isEqualTo(200L);??
- }??
?
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