java过滤器模式

前言

过滤器模式（Filter Pattern），这种模式允许开发人员使用不同的标准来过滤一组对象，通过逻辑运算以解耦的方式把它们连接起来。这种类型的设计模式属于结构型模式，它结合多个标准来获得单一标准。

过滤器模式是很多java框架常用的模式之一

1，故事

人事通过招聘，面试，从而过滤出不同水平的开发工程师，进而选择通过。

2，定义开发工程师对象

@Data
public class DevelopEngineer {
    //技能等级
    private String level;
    //姓名
    private String name;
    //年龄
    private Integer age;

    DevelopEngineer(String level,String name,Integer age){
        this.level = level;
        this.name = name;
        this.age = age;
    }

    @Override
    public String toString() {
        return "开发工程师：" +
            "{ 职业等级 ： '" + level + '\'' +
            ", 姓名：'" + name + '\'' +
            ", 年龄： " + age +
            '}';
    }
}

3，定义过滤器顶层接口 filter

public abstract class Filter {
    //筛选
    public abstract List<DevelopEngineer> choose(List<DevelopEngineer> devList);
}

4，HighDevFilter 高级开发过滤器

public class HighDevFilter extends Filter{
    //选择高级工程师
    @Override
    public List<DevelopEngineer> choose(List<DevelopEngineer> devList) {
        List<DevelopEngineer> res = new ArrayList<>();
        for (DevelopEngineer engineer : devList) {
            if(engineer.getLevel().equals("高级")){
                res.add(engineer);
            }
        }
        return res;
    }
}

5，MiddleDevFilter 中级开发过滤器

public class MiddleDevFilter extends Filter{
    //选择中级工程师
    @Override
    public List<DevelopEngineer> choose(List<DevelopEngineer> devList) {
        List<DevelopEngineer> res = new ArrayList<>();
        for (DevelopEngineer engineer : devList) {
            if(engineer.getLevel().equals("中级")){
                res.add(engineer);
            }
        }
        return res;
    }
}

6，年龄过滤器

public class AgeDevFilter extends Filter{
    @Override
    public List<DevelopEngineer> choose(List<DevelopEngineer> devList) {
        List<DevelopEngineer> res = new ArrayList<>();
        for (DevelopEngineer engineer : devList) {
            //选择出年龄小于35 大于 25 的工程师
            if(engineer.getAge() > 25 && engineer.getAge() <= 35){
                res.add(engineer);
            }
        }
        return res;
    }
}

7，测试

过滤出年龄大约25小于35的高级开发工程师

public static void main(String[] args) {
        List<DevelopEngineer> list = new ArrayList<>();
        list.add(new DevelopEngineer("高级","东升",28));
        list.add(new DevelopEngineer("高级","静子",37));
        list.add(new DevelopEngineer("中级","红岩",25));
        list.add(new DevelopEngineer("初级","晓东",30));
        list.add(new DevelopEngineer("中级","珂子",20));
        list.add(new DevelopEngineer("中级","春子",20));
        list.add(new DevelopEngineer("高级","刘一",30));
        //初始化
        HighDevFilter highDevFilter = new HighDevFilter();
        AgeDevFilter ageDevFilter = new AgeDevFilter();
        //两次过滤输出
        print(ageDevFilter.choose(highDevFilter.choose(list)));
    }

    private static void print(List<DevelopEngineer> list){
        for (DevelopEngineer engineer : list) {
            System.out.println(engineer.toString());
        }
    }

8，结果

开发工程师：{ 职业等级 ： '高级', 姓名：'东升', 年龄： 28}
开发工程师：{ 职业等级 ： '高级', 姓名：'刘一', 年龄： 30}

总结

过滤器是较为常用的设计模式之一，可以配合责任链模式，进行链式过滤