实现一：servlet 经典模式

该模式特点：多线程环境环境下，需要每一个客户端请求，new 一个ConcreteFilterChain对象。如果对象太大，增加cpu和gc的负担。

代码demo

import java.io.IOException;public interface Filter {    public void doFilter(Context ctx, FilterChain chain) throws IOException;}

import java.io.IOException;public interface FilterChain {    void doFilter(Context ctx) throws IOException;}

import java.io.IOException;public class PrintOne implements Filter {    @Override    public void doFilter(Context ctx, FilterChain chain) throws IOException {        System.out.println(Thread.currentThread().getId()+ " 1");        chain.doFilter(ctx);    }}import java.io.IOException;public class PrintTwo implements Filter {    @Override    public void doFilter(Context ctx, FilterChain chain) throws IOException {        System.out.println(Thread.currentThread().getId()+" 2");        chain.doFilter(ctx);    }}import java.io.IOException;public class PrintThree implements Filter {    @Override    public void doFilter(Context ctx, FilterChain chain) throws IOException {        System.out.println(Thread.currentThread().getId()+" 3");        chain.doFilter(ctx);    }}

import java.io.IOException;import java.util.List;public class DefaultFilterChain implements FilterChain {    public DefaultFilterChain(List
    
      list) {        this.list = list;    }    List
     
       list;    int pos = 0;    @Override    public void doFilter(Context ctx) throws IOException {        if(pos < list.size()){            Filter filter = list.get(pos);            pos++;            filter.doFilter(ctx,this);        }    }}
     
    

测试程序

import java.io.IOException;import java.util.ArrayList;import java.util.List;import java.util.concurrent.ExecutorService;import java.util.concurrent.Executors;public class TestMain {    static ExecutorService executorService = Executors.newFixedThreadPool(5);    public static void main(String args[]){        List
    
      list = new ArrayList
     
      ();        list.add(new PrintOne());        list.add(new PrintTwo());        list.add(new PrintThree());        FilterChain filterChain = new DefaultFilterChain(list);        for(int i=0;i<2;i++) {            executorService.submit(new Event(filterChain));        }    }    public static class Event implements Runnable{        public Event(FilterChain filterChain) {            this.filterChain = filterChain;        }        FilterChain filterChain;        @Override        public void run() {            Context ctx = new Context();            try {                filterChain.doFilter(ctx);            } catch (IOException e) {                e.printStackTrace();            }        }    }}
     
    

注意：该测试程序是有bug的，多线程共享filterChain会导致filter的游标定位错误。要解决这个问题，要么每个请求new一个DefaultFilterChain对象。

实现二

参考netty pipeline的实现

该实现的优点：多线程环境下，不需要每一个客户的请求都new一个DefaultFilterChain.该算法的巧妙之处在于：将handler跟filterchain 组成成一个节点。 通过handler驱动节点的扭转

上代码

public class Context {}public interface Handler {    void handle(Context ctx,FilterChain filterChain);}public class PrintOne implements Handler {    @Override    public void handle(Context ctx, FilterChain filterChain) {        System.out.println(Thread.currentThread().getId()+" 1");        filterChain.fireNext(ctx);    }}public class PrintTwo implements Handler{    @Override    public void handle(Context ctx, FilterChain filterChain) {        System.out.println(Thread.currentThread().getId()+" 2");        filterChain.fireNext(ctx);    }}public class PrintThree implements Handler {    @Override    public void handle(Context ctx, FilterChain filterChain) {        System.out.println(Thread.currentThread().getId()+" 3");        filterChain.fireNext(ctx);    }}

FilterChain和DefaultFilterChain

public interface FilterChain {    void handler(Context ctx);    void fireNext(Context ctx);}public class DefaultFilterChain implements FilterChain {    private FilterChain next;    private Handler handler;    public DefaultFilterChain(FilterChain next, Handler handler) {        this.next = next;        this.handler = handler;    }    @Override    public void handler(Context ctx) {        handler.handle(ctx,this);    }    public void fireNext(Context ctx){        FilterChain next_ = this.next;        if(next_ != null){            next_ .handler(ctx);        }    }}

测试代码

import java.util.concurrent.ExecutorService;import java.util.concurrent.Executors;public class FilterChainTest {    static ExecutorService executorService = Executors.newFixedThreadPool(3);    public static void main(String args[]){        Handler h1 = new PrintOne();        Handler h2 = new PrintTwo();        Handler h3 = new PrintThree();        FilterChain filterChain3 = new DefaultFilterChain(null,h3);        FilterChain filterChain2 = new DefaultFilterChain(filterChain3,h2);        FilterChain filterChain1 = new DefaultFilterChain(filterChain2,h1);        Context ctx = new Context();        for(int i=0;i<3;i++){            executorService.execute(new RunPrintEcho(filterChain1,ctx));        }    }    public static class RunPrintEcho implements Runnable{        FilterChain filterChain;        Context ctx;        public RunPrintEcho(FilterChain filterChain, Context ctx) {            this.filterChain = filterChain;            this.ctx = ctx;        }        @Override        public void run() {            filterChain.handler(this.ctx);        }    }}

大功告成！