Guava ---- EventBus事件驱动模型

  在软件开发过程中， 难免有信息的共享或者对象间的协作。 如何让对象间信息共享高效， 并且耦合性低， 这是一个难题。 而耦合性高将带来编码修改牵一发而动全身的连锁效应， Spring的风靡正是因为解决了高耦合问题。 本篇介绍的EventBus中也用到了Spring中的依赖注入， 来进行对象和对象间的解耦（如@Subscribe）。

  

  Guava解决高耦合采用的是事件驱动模型的思路， 对象可以订阅（subscribe）特定的事件或者发布（publish）特定的事件去被消费。 从下面的代码可以看出， EventBus对生产者和消费者是透明的， 它无需知道他们的类型， 从而实现了解耦。

TradeAccountEvent： 基本对象兼测试类  

package com.wenniuwuren.eventbus;import com.google.common.eventbus.EventBus;import java.util.Date;/** *  不管什么时候买卖交易执行， 都会产生一个TradeAccountEvent实例 */public class TradeAccountEvent {    private double amount;    private Date tradeExecutionTime;    private String tradeType;    private String tradeAccount;    public TradeAccountEvent(String account, double amount,                             Date tradeExecutionTime, String tradeType) {        this.amount = amount;        this.tradeExecutionTime =tradeExecutionTime;        this.tradeAccount = account;        this.tradeType = tradeType;    }    public static void main(String[] args) {        // 消费者和生产者根据EventBus对象来一一对应        EventBus eventBus1 = new EventBus();        SimpleTradeAuditor simpleTradeAuditor = new SimpleTradeAuditor(eventBus1);        SimpleTradeExecutor simpleTradeExecutor = new SimpleTradeExecutor(eventBus1);        simpleTradeExecutor.executeTrade("zhangsan", 10, "Money");                System.out.println("----This is devil dividing line------");                EventBus eventBus2 = new EventBus();        BuySellTradeExecutor buySellTradeExecutor = new BuySellTradeExecutor(eventBus2);        AllTradesAuditor allTradesAuditor = new AllTradesAuditor(eventBus2);        buySellTradeExecutor.executeTrade("lisi", 100, "SELL");        System.out.println("---------------------");        buySellTradeExecutor.executeTrade("wangwu", 1000, "BUY");    }}

 

AllTradesAuditor：根据不同生产者订阅不同内容

package com.wenniuwuren.eventbus;import java.util.List;import com.google.common.collect.Lists;import com.google.common.eventbus.EventBus;import com.google.common.eventbus.Subscribe;public class AllTradesAuditor {private List<BuyEvent> buyEvents = Lists.newArrayList();private List<SellEvent> sellEvents = Lists.newArrayList();public AllTradesAuditor(EventBus eventBus) {eventBus.register(this);}@Subscribepublic void auditSell(SellEvent sellEvent) {sellEvents.add(sellEvent);System.out.println("Received TradeSellEvent " + sellEvent);}@Subscribepublic void auditBuy(BuyEvent buyEvent) {buyEvents.add(buyEvent);System.out.println("Received TradeBuyEvent " + buyEvent);}}

BuyEvent：

package com.wenniuwuren.eventbus;import java.util.Date;/** * 购买事件 * @author wenniuwuren * */public class BuyEvent extends TradeAccountEvent {public BuyEvent(String tradeAccount, double amount,Date tradExecutionTime) {super(tradeAccount, amount, tradExecutionTime, "BUY");}}

SellEvent：

package com.wenniuwuren.eventbus;import java.util.Date;/** * 销售事件 * @author wenniuwuren * */public class SellEvent extends TradeAccountEvent {public SellEvent(String tradeAccount, double amount, Date tradExecutionTime) {super(tradeAccount, amount, tradExecutionTime, "SELL");}}

BuySellTradeExecutor： 分类型（BUY、SELL）发布事件

package com.wenniuwuren.eventbus;import java.util.Date;import com.google.common.eventbus.EventBus;/** * 分类型（SELL BUY）执行器 * @author wenniuwuren * */public class BuySellTradeExecutor {private EventBus eventBus;    public BuySellTradeExecutor(EventBus eventBus) {        this.eventBus = eventBus;    }private TradeAccountEvent processTrade(String tradeAccount, double amount,String tradeType) {Date executionTime = new Date();String message = String.format("Processed trade for" + tradeAccount+ "of amount" + amount + "type" + tradeType + "@"+ executionTime);TradeAccountEvent tradeAccountEvent;if (tradeType.equals("BUY")) {tradeAccountEvent = new BuyEvent(tradeAccount, amount,executionTime);} else {tradeAccountEvent = new SellEvent(tradeAccount, amount,executionTime);}System.out.println(message);return tradeAccountEvent;}public void executeTrade(String tradeAccount, double amount, String tradeType) {        TradeAccountEvent tradeAccountEvent = processTrade(tradeAccount, amount, tradeType);        // 发布, 通知订阅者        eventBus.post(tradeAccountEvent);    }}

SimpleTradeAuditor： 最简单的事件消费者（或者说订阅者）

package com.wenniuwuren.eventbus;import com.google.common.collect.Lists;import com.google.common.eventbus.EventBus;import com.google.common.eventbus.Subscribe;import java.util.List;/** * 审核交易 */public class SimpleTradeAuditor {    private List<TradeAccountEvent> tradeEvents = Lists.newArrayList();    public SimpleTradeAuditor(EventBus eventBus) {        // 注册， 以便获取TradeAccountEvent的通知        eventBus.register(this);    }    /**     * 事件处理（用@Subscribe注解表示）     * @param tradeAccountEvent     */    @Subscribe    public void auditTrade(TradeAccountEvent tradeAccountEvent) {        tradeEvents.add(tradeAccountEvent);        System.out.println("Received trade " + tradeAccountEvent);    }}

TradeBuyAuditor：分类型事件消费

package com.wenniuwuren.eventbus;import java.util.List;import com.google.common.collect.Lists;import com.google.common.eventbus.EventBus;import com.google.common.eventbus.Subscribe;/** * 购买审查 * @author wenniuwuren * */public class TradeBuyAuditor {private List<BuyEvent> buyEvents = Lists.newArrayList();public TradeBuyAuditor(EventBus eventBus) {eventBus.register(this);}@Subscribepublic void auditBuy(BuyEvent buyEvent) {buyEvents.add(buyEvent);System.out.println("Received TradeBuyEvent " + buyEvent);}public List<BuyEvent> getBuyEvents() {return buyEvents;}}

 

TradeSellAuditor： 

package com.wenniuwuren.eventbus;import java.util.List;import com.google.common.collect.Lists;import com.google.common.eventbus.EventBus;import com.google.common.eventbus.Subscribe;/** * 销售审查 * @author wenniuwuren * */public class TradeSellAuditor {private List<SellEvent> sellEvents = Lists.newArrayList();public TradeSellAuditor(EventBus eventBus) {eventBus.register(this);}@Subscribepublic void auditSell(SellEvent sellEvent) {sellEvents.add(sellEvent);System.out.println("Received SellEvent " + sellEvent);}public List<SellEvent> getSellEvents() {return sellEvents;}}

输出结果：

Processed trade forzhangsanof amount10.0typeMoney@Fri Jun 12 02:29:03 CST 2015Received trade com.wenniuwuren.eventbus.TradeAccountEvent@7c53a9eb----This is devil dividing line------Processed trade forlisiof amount100.0typeSELL@Fri Jun 12 02:29:03 CST 2015Received TradeSellEvent com.wenniuwuren.eventbus.SellEvent@14899482---------------------Processed trade forwangwuof amount1000.0typeBUY@Fri Jun 12 02:29:03 CST 2015Received TradeBuyEvent com.wenniuwuren.eventbus.BuyEvent@21588809

参考资料：

                《Getting Started with Google Guava》