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);
}
@Subscribe
public void auditSell(SellEvent sellEvent) {
sellEvents.add(sellEvent);
System.out.println("Received TradeSellEvent " + sellEvent);
}
@Subscribe
public void auditBuy(BuyEvent buyEvent) {
buyEvents.add(buyEvent);
System.out.println("Received TradeBuyEvent " + 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);
}
}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);
}
}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);
}
@Subscribe
public 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);
}
@Subscribe
public 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 2015 Received trade com.wenniuwuren.eventbus.TradeAccountEvent@7c53a9eb ----This is devil dividing line------ Processed trade forlisiof amount100.0typeSELL@Fri Jun 12 02:29:03 CST 2015 Received TradeSellEvent com.wenniuwuren.eventbus.SellEvent@14899482 --------------------- Processed trade forwangwuof amount1000.0typeBUY@Fri Jun 12 02:29:03 CST 2015 Received TradeBuyEvent com.wenniuwuren.eventbus.BuyEvent@21588809
参考资料：
《Getting Started with Google Guava》
让开发效率爆表的Guava ---- EventBus事件驱动模型
原文地址：http://blog.csdn.net/wenniuwuren/article/details/46465867
