[Design Pattern] Filter Pattern 简单案例

Filter Pattern，即过滤模式，通过不同的过滤标准，或者低耦合将过滤标准组合在一起，对一组对象进行过滤，属于结构类的设计模式。

下面是一个过滤模式的简单案例。

Criteria 定义过滤接口，CriteriaFemale, CriteriaMale, AndCriteria, OrCriteria 类实现过滤接口。Person 是被过滤的对象。CriteriaPatternDemo 演示过滤模式。

具体代码：

过滤对象 Person 的实现

public class Person {
    private String name;
    private String gender;
    private String maritalStatus;
    
    public Person(String name, String gender, String maritalStatus){
        this.name = name;
        this.gender = gender;
        this.maritalStatus = maritalStatus;
    }
    
    public String getName() {
        return name;
    }
    
    public String getGender() {
        return gender;
    }

    public String getMaritalStatus() {
        return maritalStatus;
    }
    
    public String toString(){
        return "name : " + this.name + ", gender : " + this.gender + ", maritalStatus : " + this.maritalStatus;
    }
}

过滤接口定义

import java.util.List;

public interface Criteria {
    
    public List<Person> meetCriteria(List<Person> persons);
}

CriteriaFemal, CriteriaMale, CriteriaSingle 具体类实现 Criteria 接口，实现过滤具体逻辑

import java.util.LinkedList;
import java.util.List;

public class CriteriaFemale implements Criteria {

    @Override
    public List<Person> meetCriteria(List<Person> persons) {
        
        List<Person> meetPersons = new LinkedList<>();
        for (Person p : persons){
            if ("female".equals(p.getGender())){
                meetPersons.add(p);
            }
        }
        return meetPersons;
    }
}

import java.util.LinkedList;
import java.util.List;

public class CriteriaMale implements Criteria {

    @Override
    public List<Person> meetCriteria(List<Person> persons) {
        
        List<Person> meetPersons = new LinkedList<>();
        for (Person p : persons){
            if ("male".equals(p.getGender())){
                meetPersons.add(p);
            }
        }
        return meetPersons;
    }

}

import java.util.LinkedList;
import java.util.List;

public class CriteriaSingle implements Criteria {

    @Override
    public List<Person> meetCriteria(List<Person> persons) {
        List<Person> meetPersons = new LinkedList<>();
        for (Person p : persons){
            if ("single".equals(p.getMaritalStatus())){
                meetPersons.add(p);
            }
        }
        return meetPersons;
    }
}

AndCriteria, OrCriteria 基于基本过滤具体，进行逻辑运算

import java.util.List;

public class AndCriteria implements Criteria {
    
    private Criteria criteria;
    private Criteria otherCriteria;
    
    public AndCriteria(Criteria criteria, Criteria otherCriteria){
        this.criteria = criteria;
        this.otherCriteria = otherCriteria;
    }

    @Override
    public List<Person> meetCriteria(List<Person> persons) {
        List<Person> meetPersons = criteria.meetCriteria(persons);
        meetPersons = otherCriteria.meetCriteria(meetPersons);
        return meetPersons;
    }
}

import java.util.List;

public class OrCriteria implements Criteria {

    private Criteria criteria;
    private Criteria otherCriteria;
    
    public OrCriteria(Criteria criteria, Criteria otherCriteria){
        this.criteria = criteria;
        this.otherCriteria = otherCriteria;
    }
    
    @Override
    public List<Person> meetCriteria(List<Person> persons) {
        List<Person> meetPersons1 = criteria.meetCriteria(persons);
        List<Person> meetPersons2 = otherCriteria.meetCriteria(persons);
        
        for (Person p : meetPersons2){
            if (!meetPersons1.contains(p)){
                meetPersons1.add(p);
            }
        }
        return meetPersons1;
    }
}

演示代码，对一系列对象，进行单条件过滤，或者组合条件过滤

import java.util.LinkedList;
import java.util.List;

public class CriteriaPatternDemo {

    public static void main(){
        List<Person> persons = new LinkedList<>();
        persons.add(new Person("Mike", "male", "single"));
        persons.add(new Person("Lucy", "female", "married"));
        persons.add(new Person("Vivi", "female", "single"));
        persons.add(new Person("Eric", "male", "married"));
        persons.add(new Person("Lisa", "female", "single"));
        
        System.out.println("male :");
        Criteria criteriaMale = new CriteriaMale();
        CriteriaPatternDemo.printListPerson(criteriaMale.meetCriteria(persons));
        
        System.out.println("female :");
        Criteria criteriaFemale = new CriteriaFemale();
        CriteriaPatternDemo.printListPerson(criteriaFemale.meetCriteria(persons));

        System.out.println("sinlge female :");
        Criteria criterSingle = new CriteriaSingle();
        Criteria singleFemale = new AndCriteria(criterSingle, criteriaFemale);
        CriteriaPatternDemo.printListPerson(singleFemale.meetCriteria(persons));

        System.out.println("sinlge or female :");
        Criteria singleOrFemale = new OrCriteria(criteriaFemale, criterSingle);
        CriteriaPatternDemo.printListPerson(singleOrFemale.meetCriteria(persons));

    }
    
    public static void printListPerson(List<Person> persons){
        for (Person p : persons){
            System.out.println("[" + p + "]");
        }
        System.out.println("");
    }
}

拓展性考虑

例如，要增加一个过滤标准 married 

1. 增加一个文件定义 CriteriaMarried 类，使其实现 Criteria 接口，实现过滤逻辑 meetCriteria() 

2. 在客户端 CriteriaPatternDemo 使用新增的类 CriteriaMarried 

既可使用新扩展的过滤标准。

参考资料

Design Patterns - Filter Pattern, TutorialsPoint