过滤器设计模式

过滤器设计模式：按照指定的顺序进行过滤，由一个过滤器链接口，一个起切换作用的过滤器链接口实现类，若干个过滤器链接口实现类，一个过滤器链适配器类组成。

过滤器链接口：

package com.example.ssm.filter;

import javax.servlet.http.HttpServletRequest;

/**
 * 过滤器链接口
 */
public interface FilterChain {
    void doFilter(HttpServletRequest request, FilterChain chain);
}

 

起切换作用的过滤器链接口实现类：

package com.example.ssm.filter;

import com.google.common.collect.Lists;
import org.springframework.util.CollectionUtils;

import javax.servlet.http.HttpServletRequest;
import java.util.List;

/**
 * 主过滤器链，起衔接作用
 */
public class MainChain implements FilterChain {

    private List<FilterChain> filterChains = Lists.newArrayList();

    private int index = 0;

    @Override
    public void doFilter(HttpServletRequest request, FilterChain chain) {
        if (CollectionUtils.isEmpty(filterChains)) {
            return;
        }
        FilterChain filterChain = filterChains.get(index++);
        filterChain.doFilter(request, chain);
    }

    public void addFilter(FilterChain chain) {
        filterChains.add(chain);
    }
}

 

若干个过滤器链实现类：

package com.example.ssm.filter;

import javax.servlet.http.HttpServletRequest;

/**
 * 第一个过滤器链
 */
public class FirstChain implements FilterChain {
    @Override
    public void doFilter(HttpServletRequest request, FilterChain chain) {
        System.out.println("first step");
        chain.doFilter(request,chain);
        System.out.println("five step");
    }
}

 

package com.example.ssm.filter;

import javax.servlet.http.HttpServletRequest;

/**
 * 第二个过滤器链
 */
public class TwoChain implements FilterChain {
    @Override
    public void doFilter(HttpServletRequest request, FilterChain chain) {
        System.out.println("two step");
        chain.doFilter(request,chain);
        System.out.println("four step");
    }
}

 

package com.example.ssm.filter;

import javax.servlet.http.HttpServletRequest;

/**
 * 第三个过滤器链
 * 最后的过滤器链类中doFilter方法里不要调用chain.doFilter方法
 */
public class ThreeChain implements FilterChain {

    @Override
    public void doFilter(HttpServletRequest request, FilterChain chain) {
        System.out.println("Three step");
    }
}

 

过滤器链适配器类：

package com.example.ssm.filter;

/**
 * 过滤器链适配器
 */
public class Adapter {

    private void executeChain() {
        MainChain mainChain = new MainChain();
        mainChain.addFilter(new FirstChain());
        mainChain.addFilter(new TwoChain());
        mainChain.addFilter(new ThreeChain());
        System.out.println("过滤器执行开始");
        mainChain.doFilter(null, mainChain);
        System.out.println("过滤器执行结束");
    }

    public static void main(String[] args) {
        new Adapter().executeChain();
    }
}

 

程序运行结果：

过滤器执行开始
first step
two step
Three step
four step
five step
过滤器执行结束