[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