java设计模式之责任链模式

责任链模式也是行为型模式的一种，就是上每个对象都持有对下一个对象的引用，形成一条链，最上层的对象可以通过对下一个对象的引用，将请求传递给链中的任意一个对象。

为了说明责任链的用途，在这里先写一个没有使用责任链的例子

public interface GVnment {

	/**
	 * 处理事情
	 */
	public void HandleMess();
}

public class People {

	int things;
	
	public People(int things){
		this.things = things;
	}

	public int getThings() {
		return things;
	}

	public void setThings(int things) {
		this.things = things;
	}
	
}

public class TownGVment implements GVnment{

	@Override
	public void HandleMess(People p) {
		System.out.println("人要做的事是:"+p.getThings());
		System.out.println("我这个乡镇府可以办");
	}

}

public class CityGVment implements GVnment{

	@Override
	public void HandleMess(People p) {
		System.out.println("人要做的事是:"+p.getThings());
		System.out.println("我这个市镇府可以办");
	}

}

上面要演示的是，一个人去政府机构办事，根据这个人要办的事情决定是在乡镇府办还是在市政府办，接下来测试演示这一个过程。

public class test {
	public static void main(String[] args) {
		People weakP = new People(0);
		if(weakP.getThings()==0){
			GVnment tgVnment = new TownGVment();
			tgVnment.HandleMess(weakP);
		}else if(weakP.getThings()==1){
			GVnment cgVnment = new CityGVment();
			cgVnment.HandleMess(weakP);
		}
		People weakPS = new People(1);
		if(weakPS.getThings()==0){
			GVnment tgVnment = new TownGVment();
			tgVnment.HandleMess(weakPS);
		}else if(weakPS.getThings()==1){
			GVnment cgVnment = new CityGVment();
			cgVnment.HandleMess(weakPS);
		}
	}
}

这里我们可以看得出来，我们调用者使用起来会比较麻烦，最可怜的就是这个people，不知道自己的事情哪里可以办，得一个一个试。所以就让责任链来解救他吧！！

责任链模式中我们只需要将people传递进去，至于谁去实现我们不用关心。

public abstract class GVnment {

	/**
	 * 能做的事
	 */
	private int wiCan;
	private GVnment nextGVnment;
	
	public GVnment(int canDo){
		wiCan = canDo;
	}
	/**
	 * 处理事情
	 */
	public void HandleMess(People p){
		if(p.getThings()==wiCan){
			Handle(p);
		}else{
			
			if(nextGVnment!=null){				
				nextGVnment.HandleMess(p);
			}else{
				System.out.println("没人处理得了");
			}
		}
	}
	
	public GVnment getNextGVnment() {
		return nextGVnment;
	}
	public void setNextGVnment(GVnment nextGVnment) {
		this.nextGVnment = nextGVnment;
	}
	protected abstract void Handle(People p);
}

public class TownGVment extends GVnment{

	public TownGVment() {
		super(0);
	}

	@Override
	protected void Handle(People p) {
		System.out.println("人要做的事是:"+p.getThings());
		System.out.println("我这个乡镇府可以办");
	}

}

public class CityGVment extends GVnment{

	public CityGVment() {
		super(1);
		// TODO Auto-generated constructor stub
	}

	@Override
	protected void Handle(People p) {
		System.out.println("人要做的事是:"+p.getThings());
		System.out.println("我这个市镇府可以办");
	}

}

people类没有变化，接下来看下测试类我们的使用方式

public class test {
	public static void main(String[] args) {
		People p = new People(0);
		People happyP = new People(1);
		GVnment tGv = new TownGVment();
		GVnment cGv = new CityGVment();
		tGv.setNextGVnment(cGv);
		tGv.HandleMess(p);
		tGv.HandleMess(happyP);
	}
}

调用变得简单了很多，只要建立了链在使用时就不用关心谁去实现的。这个责任链的缺点就是如果链太长了逻辑复杂了就不好维护。