四：责任链模式

责任链模式：根据一条链路执行代码
以下代码逻辑：
ABC 三个filter
处理request 时，执行链条为 A->B->C
处理reponse时，执行链条为 C->B->A
实现思路：递归

public class FilterChainDemo {

    public static void main(String[] args) {
        String request = "request";

        String response = "response";

        Filter filter = new HtmlFilter();
        Filter filter1 = new UrlFilter();

        FilterChain filterChain = new FilterChain().addFilter(filter).addFilter(filter1).addFilter(new ThreeFilter());

        filterChain.doFilter(request, response);

    }


}


class FilterChain {

    List filterList = Lists.newArrayList();
    // 通过 index 指定下一个要执行的filter
    int index = 0;

    public FilterChain addFilter(Filter filter) {
        filterList.add(filter);
        return this;
    }

    public void doFilter(String request, String response) {
        if (index >= filterList.size()) {
            return;
        }

        Filter filter = filterList.get(index);
        // index++ 需要放到 doFilter 之前，否则递归会栈溢出
        index++;
        filter.doFilter(request, response, this);

    }
}

interface Filter {

    void doFilter(String request, String response, FilterChain filterChain);

}

class HtmlFilter implements Filter {

    @Override
    public void doFilter(String request, String response, FilterChain filterChain) {


        System.out.println(request + ":HtmlFilter");

        // filterChain.doFilter 开始递归，放在处理response 之前，request处理之后才开始处理response
        filterChain.doFilter(request, response);

        System.out.println(response + ":HtmlFilter");


    }
}

class UrlFilter implements Filter {

    @Override
    public void doFilter(String request, String response, FilterChain filterChain) {

        System.out.println(request + ":UrlFilter");
        // filterChain.doFilter 开始递归，放在处理response 之前，request处理之后才开始处理response
        filterChain.doFilter(request, response);

        System.out.println(response + ":UrlFilter");


    }
}


class ThreeFilter implements Filter {

    @Override
    public void doFilter(String request, String response, FilterChain filterChain) {

        System.out.println(request + ":ThreeFilter");
        // filterChain.doFilter 开始递归，放在处理response 之前，request处理之后才开始处理response
        filterChain.doFilter(request, response);

        System.out.println(response + ":ThreeFilter");


    }
}