责任链模式平常没怎么用过，今天看到了责任链模式的基本构成。大体就是把一件事情分给n个互相有引用的类去执行。比如解析ip地址。过程如图：

package com.cn.test;import java.util.Random;/*** Created by user on 2015/9/17.*/
public abstract  class DnsServer {private DnsServer upper;public  final Recorder resolver(String domain){Recorder recorder=null;if(isLocal(domain)){recorder=echo(domain);}else {recorder=upper.resolver(domain);}return recorder;}public void setUpperServer(DnsServer _upperServer){this.upper=_upperServer;}protected  abstract  boolean isLocal(String domain);protected  Recorder echo(String domain){Recorder recorder=new Recorder();recorder.setIp(getIpAddress());recorder.setDomain(domain);return recorder;}
private String getIpAddress(){Random random =new Random();String address=random.nextInt(255)+"."+random.nextInt(255)+"."+random.nextInt(255)+"."+random.nextInt(255);return address;
}} package com.cn.test;/*** Created by user on 2015/9/17.*/
public class SHDnsServer extends  DnsServer {@Overrideprotected boolean isLocal(String domain) {return domain.endsWith(".sh.cn");}protected  Recorder echo(String domain){Recorder recorder=super.echo(domain);recorder.setOwner("上海服务器");recorder.setDomain(domain);return recorder;}
}package com.cn.test;/*** Created by user on 2015/9/17.*/
public class ChinaTopDnsServer extends  DnsServer {@Overrideprotected boolean isLocal(String domain) {return domain.endsWith(".cn");}protected  Recorder echo(String domain){Recorder recorder=super.echo(domain);recorder.setOwner("中国服务器");recorder.setDomain(domain);return recorder;}
}package com.cn.test;import java.io.BufferedReader;
import java.io.InputStreamReader;/*** Created by user on 2015/9/17.*/
public class TopDnsServer  extends  DnsServer {@Overrideprotected boolean isLocal(String domain) {return domain.endsWith(".cn");}protected  Recorder echo(String domain){Recorder recorder=super.echo(domain);recorder.setOwner("定级服务器");recorder.setDomain(domain);return recorder;}public static  void  main(String[] args) throws Exception{DnsServer shdnsServer = new SHDnsServer();DnsServer chinaServer =new ChinaTopDnsServer();DnsServer topDnsServer =new TopDnsServer();chinaServer.setUpperServer(topDnsServer);shdnsServer.setUpperServer(chinaServer);System.out.println("解析过程开始---------------");while(true){System.out.println("\n输入域名，n退出");String domain =(new BufferedReader(new InputStreamReader(System.in))).readLine();if(domain.equalsIgnoreCase("n")){return;}else{Recorder recorder=shdnsServer.resolver(domain);System.out.println("解析结果------------");System.out.println(recorder);}}}}

结果：

解析过程开始---------------

输入域名，n退出
www.baidu.cn
解析结果------------
域名：www.baidu.cn
IP地址：217.131.195.29
解析者：中国服务器

输入域名，n退出
www.baidu.sh.cn
解析结果------------
域名：www.baidu.sh.cn
IP地址：91.109.63.60
解析者：上海服务器

输入域名，n退出
n

观察者模式可以和责任链模式结合，这种结合的好处就是能够屏蔽一些责任链的细节，把责任链的低端（上海服务器）给观察者，那么责任就沿着链一直上传解决。

package com.cn.test;import java.util.Observable;
import java.util.Observer;
import java.util.Random;/*** Created by user on 2015/9/17.*/
public  abstract  class DnsServerObserver extends Observable implements Observer{public  void update(Observable arg0,Object arg1){Recorder recorder=(Recorder)arg1;if(isLocal(recorder)){recorder.setIp(getIpAddress());}else{responseFromUpperServer(recorder);}sign(recorder);}protected abstract void sign(Recorder recorder);public  void setUpperServer(DnsServerObserver dnsServer){super.deleteObservers();super.addObserver(dnsServer);}private   void responseFromUpperServer(Recorder recorder){super.setChanged();;super.notifyObservers(recorder);}protected  abstract  boolean isLocal(Recorder domain);protected  Recorder echo(String domain){Recorder recorder=new Recorder();recorder.setIp(getIpAddress());recorder.setDomain(domain);return recorder;}private String getIpAddress(){Random random =new Random();String address=random.nextInt(255)+"."+random.nextInt(255)+"."+random.nextInt(255)+"."+random.nextInt(255);return address;}} package com.cn.test;/*** Created by user on 2015/9/17.*/
public class SHDnsServer1 extends DnsServerObserver {@Overrideprotected void sign(Recorder recorder) {recorder.setOwner("上海服务器");}@Overrideprotected boolean isLocal(Recorder domain) {return domain.getDomain().endsWith(".sh.cn");}
}package com.cn.test;/*** Created by user on 2015/9/17.*/
public class ChinaTopDnsServer1 extends DnsServerObserver {@Overrideprotected void sign(Recorder recorder) {recorder.setOwner("中国服务器");}@Overrideprotected boolean isLocal(Recorder domain) {return domain.getDomain().endsWith(".cn");}
}package com.cn.test;import java.io.BufferedReader;
import java.io.InputStreamReader;/*** Created by user on 2015/9/17.*/
public class TopDnsServer1 extends DnsServerObserver {@Overrideprotected void sign(Recorder recorder) {recorder.setOwner("定级服务器");}@Overrideprotected boolean isLocal(Recorder domain) {return true;}public static  void main(String[] args) throws Exception{DnsServerObserver shdnsServer = new SHDnsServer1();DnsServerObserver chinaServer =new ChinaTopDnsServer1();DnsServerObserver topDnsServer =new TopDnsServer1();chinaServer.setUpperServer(topDnsServer);shdnsServer.setUpperServer(chinaServer);System.out.println("解析过程开始---------------");while(true){System.out.println("\n输入域名，n退出");String domain =(new BufferedReader(new InputStreamReader(System.in))).readLine();if(domain.equalsIgnoreCase("n")){return;}else{/*  Recorder recorder=shdnsServer.resolver(domain);*/Recorder recorder =new Recorder();recorder.setDomain(domain);shdnsServer.update(null,recorder);System.out.println("解析结果------------");System.out.println(recorder);}}}
}

该模式的缺陷就是不会知道具体的哪个服务器解析了域名，只返回时上海服务器解析了域名（因为上海服务器作为了观察者去处理请求）。