使用javascript和java模仿实现事件回调机制

来源：互联网发布：魔兽争霸软件下载编辑：程序博客网时间：2024/05/16 17:05

最近在学习nodejs中的eventEmitter类的时候。被它的事件注册回调机制的编程风格所吸引。于是决定使用javascript和java来模仿实现这种机制。

nodejs代码

//event.js 文件var events = require('events'); var emitter = new events.EventEmitter(); emitter.on('someEvent', function(arg1, arg2) { console.log('listener1', arg1, arg2); }); emitter.on('someEvent', function(arg1, arg2) { console.log('listener2', arg1, arg2); }); emitter.emit('someEvent', 'arg1 参数', 'arg2 参数');

emitter使用on方法绑定事件"someEvent"，然后注册对应的回调函数。

在javascript中这种方式屡见不鲜。$('#div_id').on('click', function(){});

一.javascript实现这种机制

1.服务端代码

EventEmitter = function(){var eventsMap = {};var _this = this;var on = function( name, callback ){var callbackList = eventsMap[name] || [];callbackList.length > 0? ( eventsMap = eventsMap ):( eventsMap[name] = callbackList );return callbackList.push(callback);};var emit = function(){var name = Array.prototype.shift.call(arguments);var callbackList = eventsMap[name];for( var i = 0,len = callbackList.length; i < len; i++ ){var result = callbackList[i].apply( _this, arguments );if( result != void 0 ){return false;}}return true;}var remove = function(name){return delete eventsMap.name;}return {"on" : on,"emit" : emit,"remove": remove};}

2.客户端代码

var event = new EventEmitter();event.on("click", function( data ){console.log("click1...");console.log( data.name );});event.on("click", function( data ){console.log("click2...");console.log( data.name );});event.on("mouseover", function( data ){console.log("mouseover...");console.log( data.age + ":" + data.add );});event.emit( "click", {"name": 'lilei} );event.emit( "mouseover", {"age": 12, "add": "shanghai"} );

二.java实现这种机制

1.编写接口EventService

package inter;public interface EventService {void on( String eventName, EventHandler e );void remove( String eventName );void trigger( String eventName );}

2.编写接口EventHandler

package inter;public interface EventHandler {void callback( EventService eventService );}

3.编写服务端实现类EventEmitter

package interimpl;import inter.EventService;import inter.EventHandler;import java.util.ArrayList;import java.util.HashMap;import java.util.List;import java.util.Map;public class EventEmitter implements EventService {private Map< String, List<EventHandler> >  eventMap = new HashMap< String, List<EventHandler> >();@Overridepublic void on(String eventName, EventHandler EventHandler) {List<EventHandler> callbackList = eventMap.get(eventName);if( null == callbackList ){ callbackList =  new ArrayList<EventHandler>();}if( callbackList.isEmpty() ){eventMap.put(eventName, callbackList);}callbackList.add(EventHandler);}@Overridepublic void remove(String eventName) {eventMap.remove( eventName );}@Overridepublic void trigger( String eventName ) {List<EventHandler> callbackList = eventMap.get(eventName);for( EventHandler inter : callbackList ){inter.callback(this);}}}

4.编写测试客户端

package client;import inter.EventService;import inter.EventHandler;import interimpl.EventEmitter;public class Test {public static void main(String[] args) {// TODO Auto-generated method stubEventEmitter event = new EventEmitter();event.on("click", new EventHandler() {@Overridepublic void callback(EventService e) {System.out.println("click...");e.trigger("mouseover");}});event.on("mouseover", new EventHandler() {@Overridepublic void callback(EventService EventService) {System.out.println("mouseover...");}});event.trigger("click");//event.trigger("mouseover");}}

总结：主要基于观察者的设计模式。采用客户端和服务端分离的思想。使用函数“on”对客户端的回调函数callback进行注册。采用callbackLIst对同一个事件上的回调函数进行存储。最后把每个事件所对应的各自的回调函数列表映射到map中。

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