设计模式-责任链

责任链模式（Chain of Responsibility Pattern）在众多的框架中使用的非常普遍，例如SpringMVC、SpringSecurity等。责任链模式就是要将执行的逻辑串联起来，同时可以随时在链中的某一节点结束。那么下面用简短的代码来实现该模式

public class FilterChainTest {

    /**
     * 1,定义一个链的抽象
     * */
    interface Chain{
        void doFilter(String request,String response) ;
    }

    /**
     * 2,定义一个用于处理具体业务逻辑的接口
     * */
    interface Filter {
        void doFilter(String request,String response,Chain chain);
    }

    /**
     * 实现自定义的链
     * */
    public static class MyChain implements Chain{

        private  List<Filter> filters  ;
        private Iterator<Filter> iterator ;

        public MyChain(List<Filter> filters){
            this.filters = filters ;
            iterator = filters==null?null:filters.listIterator() ;
        }

        /**
         * 执行责任链中保存的Filter实例。
         * 是否要继续执行链上后续的Filter由具体的Filter决定【当然这只是一种策略，还可以
         * 根据返回值来判断是否要继续执行后续的Filter等】
         * */
        @Override
        public void doFilter(String request, String response) {
            if(iterator == null || !iterator.hasNext()){
                return;
            }
            iterator.next().doFilter(request,response,this);
        }
    }

    public static class MyFilter implements Filter{

        private String msg ;

        public MyFilter(String msg){
            this.msg = msg ;
        }

        @Override
        public void doFilter(String request, String response, Chain chain) {
            System.out.println("hello " + msg);
            //继续执行调用链后面的Filter
            chain.doFilter(request,response);
            System.out.println("finish " + msg);
        }
    }

    public static void main(String[] args){
        //创建多个Filter，并放入到集合
        MyFilter filter1 = new MyFilter("first") ;
        MyFilter filter2 = new MyFilter("second") ;
        MyFilter filter3 = new MyFilter("third") ;
        List<Filter> filterList = new ArrayList<>() ;
        filterList.add(filter1) ;
        filterList.add(filter2) ;
        filterList.add(filter3) ;

        //构造责任链对象，并开始执行
        MyChain myChain = new MyChain(filterList) ;
        myChain.doFilter("request","response");
    }
}

执行后的打印结果

hello first
hello second
hello third
finish third
finish second
finish first