J2EE设计模式-Intercepting Filter

ntercepting 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：

Java代码  收藏代码
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。

Java代码  收藏代码
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); 
    } 
 
}