观察者模式总结
观察者模式由两部分组成：观察者、主题。
观察者模式的核心思想：当主题发生变化是，告知全部有观察者。
观察者模式的实现方法：观察者模式实现方式分两种 推送模式【push】和索取模式【pull】，共同点主题持有观察者，当有变化时通知观察者.差别在于消息的传递：
观察者模式的用途：消息广播的一种解决方式。推送模式： 由主题将消息传递给观察者，消息包括主题中全部实用值。
索取模式： 由主题将自身的引用值传递给观察者。由观察者决定须要获取哪些值是必要的。
观察者模式的缺点：1.当观察者数量比較多时，遍历观察者会减少性能。2.尽量避免闭环，在遍历是会造成系统假死。
简单演示样例
模拟新闻推送。包括主体：server。client。当server接收到信息时，将消息推送给各种client
推送模式
package observerpattern.server;
import observerpattern.client.Observer;
/**
* 主题接口
*/
public interface Observable {
/**
* 向主题中加入观察者
*
* @param ob
* @return
*/
String add(Observer ob);
/**
* 从主题中移出观察者
*
* @param ob
* @return
*/
String remove(Observer ob);
/**
* 发送消息
*
* @param msg
* @return
*/
String sendMessage(Message msg);
}
package observerpattern.server;
import java.util.ArrayList;
import java.util.List;
import observerpattern.client.Observer;
public class Server implements Observable{
private List<Observer> ls = new ArrayList<Observer>();
@Override
public String add(Observer ob) {
if(ob != null && !ls.contains(ob))
ls.add(ob);
return Constants.SUCCESS;
}
@Override
public String remove(Observer ob) {
if(ob!=null && ls.contains(ob))
ls.remove(ob);
return Constants.SUCCESS;
}
@Override
public String sendMessage(Message msg) {
for (Observer ob : ls)
{
ob.showMessage(msg);
}
return Constants.SUCCESS;
}
}
package observerpattern.server;
public class Message {
private String title;
private String contents;
private String time;
public String getTitle() {
return title;
}
public void setTitle(String title) {
this.title = title;
}
public String getContents() {
return contents;
}
public void setContents(String contents) {
this.contents = contents;
}
public String getTime() {
return time;
}
public void setTime(String time) {
this.time = time;
}
}
package observerpattern.server;
public class Constants {
private Constants(){}
public static final String SUCCESS = "success"; //成功
}
package observerpattern.client;
import observerpattern.server.Message;
/**
* 观察者接口
*/
public interface Observer {
/**
* 显示消息
*
* @param msg
* @return
*/
void showMessage(Message msg);
}
package observerpattern.client;
import observerpattern.server.Message;
public class Client implements Observer{
private String name;
public Client(String name)
{
this.name = name;
}
@Override
public void showMessage(Message msg) {
System.out.println(name+":Title->"+msg.getTitle()+" Time->"+msg.getTime()+" Contents->"+msg.getContents());
}
}
索取模式
依据推送模式，进行简单改动
package observerpattern.server;
import observerpattern.client.Observer;
/**
* 主题接口
*/
public interface Observable {
/**
* 向主题中加入观察者
*
* @param ob
* @return
*/
String add(Observer ob);
/**
* 从主题中移出观察者
*
* @param ob
* @return
*/
String remove(Observer ob);
/**
* 发送消息
*
* @param msg
* @return
*/
String sendMessage(Message msg);
/**
* 将信息传递给观察者
*
* @param msg
*/
void notifyObservers();
}
package observerpattern.server;
import java.util.ArrayList;
import java.util.List;
import observerpattern.client.Observer;
public class Server implements Observable{
private List<Observer> ls = new ArrayList<Observer>();
@Override
public String add(Observer ob) {
if(ob != null && !ls.contains(ob))
ls.add(ob);
return Constants.SUCCESS;
}
@Override
public String remove(Observer ob) {
if(ob!=null && ls.contains(ob))
ls.remove(ob);
return Constants.SUCCESS;
}
@Override
public String sendMessage(Message msg) {
this.msg = msg;
notifyObservers();
return Constants.SUCCESS;
}
private Message msg = null;
@Override
public void notifyObservers() {
for (Observer ob : ls) {
ob.saveMessage(msg);
}
}
}
package observerpattern.server;
public class Message {
private String title;
private String contents;
private String time;
public String getTitle() {
return title;
}
public void setTitle(String title) {
this.title = title;
}
public String getContents() {
return contents;
}
public void setContents(String contents) {
this.contents = contents;
}
public String getTime() {
return time;
}
public void setTime(String time) {
this.time = time;
}
}
package observerpattern.server;
public class Constants {
private Constants(){}
public static final String SUCCESS = "success"; //成功
}
package observerpattern.client;
import observerpattern.server.Message;
/**
* 观察者接口
*/
public interface Observer {
/**
* 显示消息
*
* @param msg
* @return
*/
void showMessage();
void saveMessage(Message msg);
}
package observerpattern.client;
import observerpattern.server.Message;
public class Client implements Observer{
private String name;
private Message msg = null;
public Client(String name)
{
this.name = name;
}
@Override
public void showMessage() {
System.out.println(name+":Title->"+msg.getTitle()+" Time->"+msg.getTime()+" Contents->"+msg.getContents());
}
@Override
public void saveMessage(Message msg) {
this.msg = msg;
}
}
package observerpattern.test;
import observerpattern.client.Client;
import observerpattern.client.Observer;
import observerpattern.server.Message;
import observerpattern.server.Observable;
import observerpattern.server.Server;
public class Test {
public static void main(String[] args) {
Observable server = new Server();
Observer ob1 = new Client("phone");
Observer ob2 = new Client("pad");
Observer ob3 = new Client("computer");
server.add(ob1);
server.add(ob2);
server.add(ob3);
Message msg = new Message();
msg.setTitle("新闻标题");
msg.setTime("2014/10/31");
msg.setContents("都是呵呵啊");
server.sendMessage(msg);
ob1.showMessage();
}
}
执行结果
phone:Title->新闻标题 Time->2014/10/31 Contents->都是呵呵啊
