设计模式 行为型模式 -- 职责链模式（JDK源码分析：FilterChain（过滤器））

Posted 2021-12-02 CodeJiao

设计模式 行为型模式 – 职责链模式（定义、结构、纯与不纯的职责链模、具体案例）

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1. JDK源码分析：FilterChain

下面的代码都是模拟源码仿写的，是为了简化代码，突出的是职责链模式的思想。

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1.1 模拟web请求Request以及web响应Response

Request.java

package com.tian.responsibility.jdk;

/**
 * @version v1.0
 * @ClassName: Request
 */
public interface Request {
}

Response.java

package com.tian.responsibility.jdk;

/**
 * @version v1.0
 * @ClassName: Response
 * @Description: TODO(一句话描述该类的功能)
 * @Author: 黑马程序员
 */
public interface Response {
}

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1.2 模拟web过滤器Filter

Filter.java

package com.tian.responsibility.jdk;

/**
 * @version v1.0
 * @ClassName: Filter
 */
public interface Filter {
    public void doFilter(Request req, Response res, FilterChain c);
}

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1.3 模拟实现具体过滤器

FirstFilter.java

package com.tian.responsibility.jdk;

/**
 * @version v1.0
 * @ClassName: FirstFilter
 */
public class FirstFilter implements Filter {
    public void doFilter(Request req, Response res, FilterChain chain) {
        System.out.println("过滤器1 前置处理");

        // 先执行所有request再倒序执行所有response
        chain.doFilter(req, res);

        System.out.println("过滤器1 后置处理");
    }
}

SecondFilter.java

package com.tian.responsibility.jdk;

/**
 * @version v1.0
 * @ClassName: FirstFilter
 */
public class SecondFilter implements Filter {
    public void doFilter(Request req, Response res, FilterChain chain) {
        System.out.println("过滤器2 前置处理");

        // 先执行所有request再倒序执行所有response
        chain.doFilter(req, res);

        System.out.println("过滤器2 后置处理");
    }
}

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1.4 模拟实现过滤器链FilterChain

package com.tian.responsibility.jdk;

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

/**
 * @version v1.0
 * @ClassName: FilterChain
 */
public class FilterChain { //过滤器链

    private List<Filter> filters = new ArrayList<Filter>();

    private int index = 0;

    // 构造职责类：链式调用
    public FilterChain addFilter(Filter filter) {
        this.filters.add(filter);
        return this;
    }

    public void doFilter(Request request, Response response) {
        if (index == filters.size()) {
            return;
        }
        Filter filter = filters.get(index);
        index++;
        filter.doFilter(request, response, this);
    }
}

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1.5 客户端类：测试类

package com.tian.responsibility.jdk;

/**
 * @version v1.0
 * @ClassName: Client
 * @Description: 客户端类：测试类
 */
public class Client {
    public static void main(String[] args) {
        Request req = null;
        Response res = null;

        FilterChain filterChain = new FilterChain();
        filterChain.addFilter(new FirstFilter()).addFilter(new SecondFilter());
        filterChain.doFilter(req, res);
    }
}

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1.6 运行结果

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