责任链模式

为某个请求创建一个对象链。每个对象依次序检查次请求，并对其处理或者传递给对象链中的下一个对象。

类图

 

 （图来自wiki）

示例

public class Request {
    private int num;
    public Request(int num){
        this.num=num;
    }

    public int getNum() {
        return num;
    }
}

public interface Chain {
    void setNext(Chain nextChain);
    void doSomething(Request request);
}

public class ChainA implements Chain{
    private Chain nextChain;
    @Override
    public void setNext(Chain nextChain) {
        this.nextChain = nextChain;
    }

    @Override
    public void doSomething(Request request) {
        if(request.getNum()>0){
            System.out.println("ChainA works!");
        }
        if(nextChain!=null){
            nextChain.doSomething(request);
        }
    }
}

public class ChainB implements Chain{
    private Chain nextChain;
    @Override
    public void setNext(Chain nextChain) {
        this.nextChain = nextChain;
    }

    @Override
    public void doSomething(Request request) {
        if(request.getNum()==0){
            System.out.println("ChainB works!");
        }
        if(nextChain!=null){
            nextChain.doSomething(request);
        }
    }
}

public class ChainC implements Chain{
    private Chain nextChain;
    @Override
    public void setNext(Chain nextChain) {
        this.nextChain = nextChain;
    }

    @Override
    public void doSomething(Request request) {
        if(request.getNum()<0){
            System.out.println("ChainC works!");
        }
        if(nextChain!=null){
            nextChain.doSomething(request);
        }
    }
}

//测试
public class Client {
    public static void main(String[] args){
        Chain chainA = new ChainA();
        Chain chainB = new ChainB();
        Chain chainC = new ChainC();
        chainA.setNext(chainB);
        chainB.setNext(chainC);
        System.out.println("****************");
        chainA.doSomething(new Request(1));
        System.out.println("****************");
        chainA.doSomething(new Request(0));
        System.out.println("****************");
        chainA.doSomething(new Request(-1));
    }
}

运行结果