概念
首先说明一下,发布-订阅模式并不等同于观察者模式,这两者是有区别的。举例说明,用户直接向出版社订阅杂志,出版社直接把杂志发送给订阅杂志的用户,这种场景就是观察者模式。而发布-订阅模式则不同,出版社和用户并不直接接触,用户是向邮局订阅杂志,出版社向邮局发布杂志后,邮局再向用户派送杂志。也就是说,发布-订阅模式是有一个中转调度中心的。如下图:
上图发布订阅模式进行抽象如下图,借图一用:
发布订阅模式角色
- 发布者:消息或者说主题的生产者。
- 订阅者:订阅消息或主题的消费者。
- 调度中心/消息管理器:生产者发布消息与消费者订阅消息的中转站,调度作用。
- 主题:也称消息,生产者生产与消费者使用的内容。
代码实现
案例场景:拓展《设计模式入门–观察者模式》案例二场景(资讯网站每天给注册用户推送新闻)为:很多自媒体作者向资讯网站投内容,文章被采用后,适时给注册用户推送文章。作者是消息发布者,注册用户是订阅者,调度中心是网站平台,主题则为内容(文章、广告、活动)。
思路:其实就是实现上述四个角色,这里以最简单的方式实现。
发布者:能够向平台提交内容
订阅者:能够从平台获取推送的内容、然后读内容
内容:文章、广告、活动,就是一个封装的实体类
调度中心:能够存储发布者提交的内容,能够添加、删除订阅者,能够推送消息给订阅者
发布者->
- 抽象发布者基类
package learn.publishsubscribe.example;
/**
* 抽象发布者
* Created by chao.du on 2018/2/1.
*/
public interface BaseAuthor<T> {
/**
* 发布消息(作者向网站提交文章)
* @param contentHelper 消息管理器,订阅器
*/
void pushlishContent(ContentHelper contentHelper,T content);
}
- 具体发布者
package learn.publishsubscribe.example;
/**
* 具体发布者1,作者1
* Created by chao.du on 2018/2/1.
*/
public class AuthorA<T extends BaseContent> implements BaseAuthor<T> {
private String name;
public void pushlishContent(ContentHelper contentHelper,T content) {
contentHelper.publishContentToQueue(content);
}
public AuthorA(String name) {
this.name = name;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
}
/**
* 具体发布者2,作者2
* Created by chao.du on 2018/2/1.
*/
public class AuthorB<T extends BaseContent> implements BaseAuthor<T> {
private String name;
public AuthorB(String name) {
this.name = name;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public void pushlishContent(ContentHelper contentHelper,T content) {
contentHelper.publishContentToQueue(content);
}
}
订阅者->
- 抽象订阅者基类
package learn.publishsubscribe.example;
/**
* 抽象订阅者
* Created by chao.du on 2018/2/1.
*/
public abstract class BaseReader {
/**
* 消息
*/
protected BaseContent content;
/**
* 读者名字
*/
protected String name;
public BaseReader(String name) {
this.name = name;
}
/**
* 订阅消息(注册用户向网站订阅文章)
* @param contentHelper 消息管理器,订阅器
*/
void subscribeContent(ContentHelper contentHelper){
contentHelper.addReader(this);
}
/**
* 收到内容处理器推送的消息(注册用户接手某作者的创作内容)
* @param content 文章
*/
void receiveContent(BaseContent content){
this.content=content;
String title=null;
if(content instanceof Article){
title=((Article) content).getTitle();
}else if(content instanceof Advertisement){
title=((Advertisement) content).getTitle();
}else{
title=((Activity) content).getTitle();
}
System.out.println(this.name+":收到来自【"+this.content.getWriteBy()+"】的"+this.content.getContentType()+"【"+title+"】");
this.readContent(this.content);
}
/**
* 收到消息,进行后续逻辑(读消息)
* @param content
*/
abstract void readContent(BaseContent content);
}
- 具体订阅者
package learn.publishsubscribe.example;
/**
* 具体订阅者,注册者1
* Created by chao.du on 2018/2/1.
*/
public class Reader1 extends BaseReader {
public Reader1(String name) {
super(name);
}
public void readContent(BaseContent content) {
System.out.println(this.name+"----这篇文章我读了1111");
}
}
package learn.publishsubscribe.example;
/**
* 具体订阅者,注册者2
* Created by chao.du on 2018/2/1.
*/
public class Reader2 extends BaseReader {
public Reader2(String name) {
super(name);
}
public void readContent(BaseContent content) {
System.out.println(this.name+"----这篇文章我读了2222");
}
}
package learn.publishsubscribe.example;
/**
* 具体订阅者,注册者3
* Created by chao.du on 2018/2/1.
*/
public class Reader3 extends BaseReader {
public Reader3(String name) {
super(name);
}
public void readContent(BaseContent content) {
System.out.println(this.name+"----这篇文章我读了3333");
}
}
消息->
- 消息基类
package learn.publishsubscribe.example;
import java.util.Date;
/**
* 消息类,主题,内容类型:文章、广告、活动等
* Created by chao.du on 2018/2/1.
*/
public abstract class BaseContent {
protected String contentType;
protected Date createTime;
protected String writeBy;
public BaseContent() {
this.createTime=new Date();
}
public BaseContent(String contentType) {
this.contentType=contentType;
this.createTime=new Date();
}
public BaseContent(String contentType, String writeBy) {
this.contentType=contentType;
this.writeBy=writeBy;
this.createTime=new Date();
}
public String getContentType() {
return contentType;
}
public Date getCreateTime() {
return createTime;
}
public String getWriteBy() {
return writeBy;
}
public void setWriteBy(String writeBy) {
this.writeBy = writeBy;
}
}
- 具体消息类
package learn.publishsubscribe.example;
/**
* 内容--文章类
* Created by chao.du on 2018/2/1.
*/
public class Article extends BaseContent {
/**
* 标题
*/
private String title;
/**
* 标签
*/
private String tag;
/**
* 简介
*/
private String descrition;
/**
* 正文
*/
private String content;
public Article() {
super("文章");
}
public Article(String writeBy, String title, String tag, String descrition, String content) {
super("文章",writeBy);
this.title = title;
this.tag = tag;
this.descrition = descrition;
this.content = content;
}
public String getTitle() {
return title;
}
public void setTitle(String title) {
this.title = title;
}
public String getTag() {
return tag;
}
public void setTag(String tag) {
this.tag = tag;
}
public String getDescrition() {
return descrition;
}
public void setDescrition(String descrition) {
this.descrition = descrition;
}
public String getContent() {
return content;
}
public void setContent(String content) {
this.content = content;
}
}
package learn.publishsubscribe.example;
/**
* 内容--广告类
* Created by chao.du on 2018/2/1.
*/
public class Advertisement extends BaseContent {
/**
* 广告标题
*/
private String title;
/**
* 广告banner地址
*/
private String banner;
/**
* 广告描述
*/
private String descrtion;
public Advertisement() {
super("广告");
}
public Advertisement(String writeBy, String title, String banner, String descrtion) {
super("广告",writeBy);
this.title = title;
this.banner = banner;
this.descrtion = descrtion;
}
public String getTitle() {
return title;
}
public void setTitle(String title) {
this.title = title;
}
public String getBanner() {
return banner;
}
public void setBanner(String banner) {
this.banner = banner;
}
public String getDescrtion() {
return descrtion;
}
public void setDescrtion(String descrtion) {
this.descrtion = descrtion;
}
}
package learn.publishsubscribe.example;
import java.util.Date;
/**
* 内容--活动类
* Created by chao.du on 2018/2/1.
*/
public class Activity extends BaseContent {
/**
* 活动标题
*/
private String title;
/**
* 活动介绍
*/
private String content;
/**
* 活动时间
*/
private Date date;
public Activity() {
super("活动");
}
public Activity(String title, String content, Date date) {
super("活动");
this.title = title;
this.content = content;
this.date = date;
}
public String getTitle() {
return title;
}
public void setTitle(String title) {
this.title = title;
}
public String getContent() {
return content;
}
public void setContent(String content) {
this.content = content;
}
public Date getDate() {
return date;
}
public void setDate(Date date) {
this.date = date;
}
}
调度中心->
package learn.publishsubscribe.example;
import java.util.ArrayList;
import java.util.LinkedList;
import java.util.List;
import java.util.Queue;
/**
* 消息管理器,主题调度中心,网站文章处理器
* Created by chao.du on 2018/2/1.
*/
public class ContentHelper{
/**
* 内容调度器注册订阅内容的读者(网站注册者)容器
*/
private List<BaseReader> readerList=new ArrayList<BaseReader>();
/**
* 发布者发布消息的消息存储队列
*/
private Queue<BaseContent> queue = new LinkedList();
public ContentHelper() {
}
public ContentHelper(List<BaseReader> readerList) {
this.readerList = readerList;
}
/**
* 向消息队列添加消息(供发布者发布信息调用使用)
* @param content
*/
public void publishContentToQueue(BaseContent content){
this.queue.offer(content);
for(BaseReader reader:readerList){
reader.receiveContent(content);
}
}
/**
* 向订阅者推送消息(供订阅者获取内容处理器推送的消息,订阅者调用)
* @return
*/
public void pushContentFromQueue(){
for (BaseReader reader:readerList){
reader.receiveContent(this.queue.poll());
}
}
/**
* 添加订阅者
*/
public void addReader(BaseReader reader){
this.readerList.add(reader);
}
/**
* 删除订阅者
*/
public void removeReader(BaseReader reader){
this.removeReader(reader);
}
}
客户端->
package learn.publishsubscribe.example;
/**
* 场景:很多作者向资讯平台提交消息内容(文章、广告、活动),资讯平台向平台注册用户推送消息内容
* Created by chao.du on 2018/2/2.
*/
public class Client {
public static void main(String[] args) {
//内容处理器
ContentHelper contentHelper=new ContentHelper();
//订阅人,订阅消息
new Reader1("小明").subscribeContent(contentHelper);
new Reader2("小张").subscribeContent(contentHelper);
new Reader3("小花").subscribeContent(contentHelper);
//发布人,发布消息
new AuthorA("美食博主").pushlishContent(contentHelper,new Article("美食博主","红烧肉绝佳菜谱","红烧肉","很好的红烧肉菜谱","步骤一、二、三"));
new AuthorB("广告人").pushlishContent(contentHelper,new Advertisement("广告人","营销黄金法则","http://www.baidu.com/1.jpg","学会营销。。。。。"));
}
}
运行结果->
参考资料:
1、《订阅消息模式》