EventBus:

创建EventBus实例：

EventBus eventBus = new EventBus();//或者EventBus eventBus = new EventBus(TradeAccountEvent.class.getName());//带标识符,用于日志记录

订阅事件：

• 模拟一个交易过程。

• 事件类：

/** * 事件类 */public class TradeAccountEvent {	private double amount;	private Date tradeExecutionTime;	private TradeType tradeType;	private TradeAccount tradeAccount;	public TradeAccountEvent(TradeAccount account, double amount,			Date tradeExecutionTime, TradeType tradeType) {		this.amount = amount;		this.tradeExecutionTime = tradeExecutionTime;		this.tradeAccount = account;		this.tradeType = tradeType;	}}/** * 购买事件 */public class BuyEvent extends TradeAccountEvent {	public BuyEvent(TradeAccount tradeAccount, double amount,			Date tradExecutionTime) {		super(tradeAccount, amount, tradExecutionTime, TradeType.BUY);	}}/** * 卖出事件 */public class SellEvent extends TradeAccountEvent {	public SellEvent(TradeAccount tradeAccount, double amount,			Date tradExecutionTime) {		super(tradeAccount, amount, tradExecutionTime, TradeType.SELL);	}}

• 订阅者

/** * 卖出和购买审计，即订阅者 */public class AllTradesAuditor {	private List
    
      buyEvents = Lists.newArrayList();	private List
     
       sellEvents = Lists.newArrayList();	public AllTradesAuditor(EventBus eventBus) {		eventBus.register(this);	}	/**	 * 订阅卖出事件	 */	@Subscribe	public void auditSell(SellEvent sellEvent) {		sellEvents.add(sellEvent);		System.out.println("Received TradeSellEvent " + sellEvent);	}	/**	 * 订阅购买事件	 */	@Subscribe	public void auditBuy(BuyEvent buyEvent) {		buyEvents.add(buyEvent);		System.out.println("Received TradeBuyEvent " + buyEvent);	}}
     
    

• 发布者

/** * 执行交易, 即发布者 */public class SimpleTradeExecutor {	private EventBus eventBus;	public SimpleTradeExecutor(EventBus eventBus) {		this.eventBus = eventBus;	}	/**	 * 执行交易	 */	public void executeTrade(TradeAccount tradeAccount, double amount,			TradeType tradeType) {		TradeAccountEvent tradeAccountEvent = processTrade(tradeAccount,				amount, tradeType);		eventBus.post(tradeAccountEvent); // 发布事件	}	/**	 * 处理交易	 * 	 * @return 交易事件	 */	private TradeAccountEvent processTrade(TradeAccount tradeAccount,			double amount, TradeType tradeType) {		Date executionTime = new Date();		String message = String.format(				"Processed trade for %s of amount %n type %s @ %s",				tradeAccount, amount, tradeType, executionTime);		TradeAccountEvent tradeAccountEvent;		if (tradeType.equals(TradeType.BUY)) { //购买动作			tradeAccountEvent = new BuyEvent(tradeAccount, amount,					executionTime);		} else { //卖出动作			tradeAccountEvent = new SellEvent(tradeAccount, amount,					executionTime);		}		System.out.println(message);		return tradeAccountEvent;	}}

• 测试用例

EventBus eventBus = new EventBus();AllTradesAuditor auditor = new AllTradesAuditor(eventBus);SimpleTradeExecutor tradeExecutor = new SimpleTradeExecutor(eventBus);tradeExecutor.executeTrade(new TradeAccount(), 1000, TradeType.SELL);tradeExecutor.executeTrade(new TradeAccount(), 2000, TradeType.BUY);

取消订阅：

• 订阅者来取消注册

public void unregister(){      this.eventBus.unregister(this);}

AsyncEventBus类

• 闻其名，就是异步事件总线，当处理耗时的处理时很有用，我们要依赖Executors来实现异步事件总线

AsyncEventBus asyncEventBus = new AsyncEventBus(executorService);

DeadEvents:

• 当总线接收到发布者发布的信息时，但这时没有订阅者，那么该事件会被包装为DeadEvent事件

public class DeadEventSubscriber {	private static final Logger logger = 			Logger.getLogger(DeadEventSubscriber.class.getName());	public DeadEventSubscriber(EventBus eventBus) {		eventBus.register(this);	}		/**	 * 没有订阅者时被触发	 */	@Subscribe	public void handleUnsubscribedEvent(DeadEvent event){		logger.warning("No subscribers for "+event.getEvent());	}}

依赖注入

• 我们可以通过DI框架(Spring或Guice)来注入同样的EventBus

@Componentpublic class SimpleTradeExecutor {       private EventBus eventBus;       @Autowired       public SimpleTradeExecutor(EventBus eventBus) {           this.eventBus = checkNotNull(eventBus, "EventBus can't be null");                                             }}

@Componentpublic class SimpleTradeAuditor {       private List
    
      tradeEvents =    Lists.newArrayList();    @Autowired    public SimpleTradeAuditor(EventBus eventBus){           checkNotNull(eventBus,"EventBus can't be null");           eventBus.register(this);   }}
    

不吝指正。