J2EE设计模式-Intercepting Filter

Intercepting Filter类似于职责链模式
有两种实现
其中一种是Filter之间没有联系，全部Filter都存放在FilterChain中，由FilterChain来有序或无序地把把所有Filter调用一遍。没有用到链表这种数据结构。示例如下：

package com.ljn.filter.custom;

import java.util.ArrayList;
import java.util.List;

/**
 * 由FilterManager组织FilterChain，在FilterChain里面的filter顺序执行，
 * 各Filter之间没有交互
 */
public class InterceptingFilterManager {

    interface Filter {
        void execute(String request, String response);
    }

    static class AuthenticationFilter implements Filter {

        @Override
        public void execute(String request, String response) {
            System.out.println("AuthenticationFilter");
        }

    }

    static class DebugFilter implements Filter {

        @Override
        public void execute(String request, String response) {
            System.out.println("DebugFilter");
        }
    }

    static class Target {

        public void execute(String request, String response) {
            System.out.println("Target");
        }

    }

    static class FilterChain {
        private List<Filter> filters = new ArrayList<Filter>();
        private Target target;

        public void addFilter(Filter filter) {
            filters.add(filter);
        }

        //顺序执行，各filter之间没有直接联系
        public void execute(String request, String response) {
            for (Filter filter : filters) {
                filter.execute(request, response);
            }
            target.execute(request, response);
        }

        public void setTarget(Target target) {
            this.target = target;
        }
    }
    

    public static void main(String[] args) throws Exception {
        
        Target target = new Target();
        
        Filter debugFilter = new DebugFilter();
        Filter authenticationFilter = new AuthenticationFilter();
        
        FilterChain chain = new FilterChain();
        chain.addFilter(authenticationFilter);
        chain.addFilter(debugFilter);
        chain.setTarget(target);
        
        String req = null;
        String res = null;
        chain.execute(req, res);
        
    }

}

另一种是一个Filter“持有”下一个Filter，下一个Filter的调用由上一个Filter决定。这其中就用到了链表这种数据结构。

package com.ljn.filter.custom;

/**
 * 结合装饰模式，每个filter完成自己的处理后，显式调用下一个filter
 */
public class InterceptingFilterDecorator {

    interface Filter {
        void execute(String request, String response);
    }

    static class AuthenticationFilter implements Filter {
        private Filter next;

        public AuthenticationFilter(Filter next) {
            this.next = next;
        }

        @Override
        public void execute(String request, String response) {
            System.out.println("AuthenticationFilter");
            next.execute(request, response);
        }

    }

    static class DebugFilter implements Filter {
        private Filter next;

        public DebugFilter(Filter next) {
            this.next = next;
        }

        @Override
        public void execute(String request, String response) {
            System.out.println("DebugFilter");
            next.execute(request, response);
        }
    }

    static class Target implements Filter {
        @SuppressWarnings("unused")
        private Filter next;

        public Target() {
            this(null);
        }

        public Target(Filter next) {
            this.next = next;
        }

        @Override
        public void execute(String request, String response) {
            System.out.println("Target");
            // next.execute(request, response); //last one, no need to call next
        }

    }

    public static void main(String[] args) throws Exception {
        Filter processor = new AuthenticationFilter(
                                new DebugFilter(
                                        new Target()));
        String req = null;
        String res = null;
        processor.execute(req, res);
    }

}