责任链模式详解

2年前 (2022) 程序员胖胖胖虎阿

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责任链模式

gitee代码实现地址

1. 背景

需求: 实现过滤
需求2: 直接写好，不用修改的那种的过滤，就是可以从配置文件中读取的过滤器，然后加入到过滤器队列中。
需求3：可以在决定在哪里停止过滤，不用进行下一步的过滤。
需求4：在去的时候进行一个过滤，在回来的时候进行另一个过滤。

2.实现

链式编程实现filter

package chainOfResponsibility;

import com.sun.org.apache.bcel.internal.generic.GETFIELD;

import java.util.ArrayList;
import java.util.List;
import java.util.Map;
import java.util.concurrent.Semaphore;

/*
*
* 实现方式0：在主类中进行过滤。
*
*   实现方式1，进行链式编程
*   实现方式2: 可以把链条加进来
*   实现方式3：sevlet中的过滤，递归的过程
* */
public class FilterChainI {

    public static void main(String[] args) {
        Message msg = new Message("你好 <script>, 大家都喜欢ssm");

        FilterChain fc = new FilterChain();
        fc.add(new HtmlFilter()).add(new SensitiveFilter());
        fc.doFilter(msg);
        System.out.println(msg.getMsg());
    }

}

class Message  {
    String msg;
    Message(String s) {
        this.msg = s;
    }

    public void setMsg(String msg) {
        this.msg = msg;
    }

    public String getMsg() {
        return msg;
    }
}

interface Filter {
    public void doFilter(Message s);
}

class  HtmlFilter implements Filter{
    @Override
    public void doFilter(Message s) {
        String t = s.getMsg().replaceAll("<", "[");
        t = t.replaceAll(">", "]");
        s.setMsg(t);
    }
}

class SensitiveFilter implements Filter {
    @Override
    public void doFilter(Message s) {
        String t = s.getMsg().replaceAll("ssm", "happy");
        s.setMsg(t);
    }
}

class FilterChain {
    List<Filter> filters;
    FilterChain() {
        filters = new ArrayList<>();
    }


    public FilterChain add(Filter filter) {
        filters.add(filter);
        return this;
    }
    public void doFilter(Message s) {
        for (Filter f: filters) {
            f.doFilter(s);
        }
    }
}

可以把链连接起来

package chainOfResponsibility;


import javafx.collections.transformation.FilteredList;

import java.io.File;
import java.util.ArrayList;
import java.util.List;

/*
*
*
*   实现方式2：链式添加
* */
public class FilterChainII {

    public static void main(String[] args) {
        Message msg = new Message("你好 <script>, 大家都喜欢ssm");

        FilterChain2 fc = new FilterChain2();
        fc.add(new HtmlFilter());
        fc.add(new SensitiveFilter());
        fc.doFilter(msg);
        System.out.println(msg.getMsg());
    }
}

class FilterChain2 {
    List<Filter> filters = new ArrayList<>();
    public void add(Filter f) {
        filters.add(f);
    }
    public void doFilter(Message s) {
        for (Filter f : filters) {
            f.doFilter(s);
        }
    }
}

3. 实际应用

1. 过滤器

实现1: 使用数组实现顺序表
- 使用递归调用
- fc可以说是next指针，指向下一个需要执行的filter。
- 此处的fc是使用index进行实现的
优点分析
- 控制的流程放在了filterChain里面。
- 这样就算用户没有设置next,filterChain也可以保证安全。
细节
- index–；实现可以重复使用过滤器
- 把filterChain改成 filter next更容易理解

package chainOfResponsibility;


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

/*
*
*   经典servlet的实现版本
* */
public class FilterChainIV {

    public static void main(String[] args) {
        MyFilterChain fc = new MyFilterChain();
        fc.add(new MyHtmlFilter()).add(new MySensitiveFilter());
        MyResponse res = new MyResponse();
        MyRequest req = new MyRequest();
        fc.doFilter(req, res, fc);
        System.out.println("req = " + req.msg);
        System.out.println("resp = " + res.msg);
        fc.doFilter(req, res, fc);
        System.out.println("req = " + req.msg);			// 进行二次过滤，或者进行别的过滤。
        System.out.println("resp = " + res.msg);
    }
}

class MyRequest {
    String msg = "";
}

class MyResponse {
    String msg = "";
}

interface MyFilter {
    public void doFilter(MyRequest req, MyResponse resp, MyFilter next);
}

class MyFilterChain implements MyFilter{
    List<MyFilter>filters = new ArrayList<>();
    int index = 0;

    public MyFilterChain add(MyFilter filter) {
        filters.add(filter);
        return this;
    }

    @Override
    public void doFilter(MyRequest req, MyResponse resp, MyFilter next) {
        if (index >= filters.size()) return ;
        MyFilter filter = filters.get(index);
        index++;
        filter.doFilter(req, resp, next);
        index--;                    // 进行回溯，否则没法进行重新过滤了
    }
}

class MyHtmlFilter implements MyFilter{

    @Override
    public void doFilter(MyRequest req, MyResponse resp,  MyFilter next) {
        req.msg += "Req.htmlFilter-->";
        next.doFilter(req, resp, next);           // 如果从这里不进行递归调用，就不进行下一步处理了
        resp.msg += "Resp.htmlFilter-->";
    }
}
class MySensitiveFilter implements MyFilter{
    @Override
    public void doFilter(MyRequest req, MyResponse resp, MyFilter next) {
        req.msg += "Req.sensitiveFilter-->";
        next.doFilter(req, resp, next);             // 有用户自己决定是否进行下一步的调用
        resp.msg += "Resp.sensitiveFilter-->";
    }
}

实现2：使用链表实现顺序表

package chainOfResponsibility.v5;

import java.io.FileNotFoundException;
import java.lang.reflect.Field;

/*
*
*   使用链表直接实现FilterChain
*
* 属性, Filter next
*   除了RuntimeException与其子类，以及错误（Error），其他的都是检查异常（绝对的大家族）。
*
*
* */
public class FilterChianI {

    public static void main(String[] args) {
        Filter htmlFilter = new HtmlFitler();
        htmlFilter.setNext(new SesitiveFilter());
        Requeset req = new Requeset();
        Response res = new Response();
        htmlFilter.doFilter(req, res);
        System.out.println(req.msg);
        System.out.println(res.msg);
    }
}


abstract class Filter {
    private Filter next;
    public Filter setNext(Filter next){
        this.next = next;
        return this;
    }
    public abstract void doFilter(Requeset req, Response resp);
    public Filter getNext() throws NullPointerException{
        if (this.next != null) return this.next;
        else throw new NullPointerException("没有设置next!!!请设置在调用");
    }
}
class Requeset {
    String msg = "";
}
class Response {
    String msg = "";
}

class HtmlFitler extends Filter {

    @Override
    public void doFilter(Requeset req, Response resp) {
        req.msg += "Req.htmlFilter->";
        Filter nx = super.getNext();
        nx.doFilter(req, resp);
        resp.msg += "Resp.htmlFilter->";
    }
}

class SesitiveFilter extends Filter {
    @Override
    public void doFilter(Requeset req, Response resp) {
        req.msg += "Req.sensitiveFilter->";
        //getNext().doFilter(req, resp);      // 报错
        resp.msg += "Resp.sensitiveFilter->";
    }
}