设计模式--过滤器模式

过滤器模式（Filter Pattern）

过滤器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他们连接起来。大类划分为结构型模式，它结合多个标准来获得单一标准。

介绍

意图：在保证解耦的前提下连接多个标准来过滤一组对象。
应用场景：过滤标准较多，且分散。
优点：1. 解耦性高。2. 连接过滤对象的多组标准时，减轻了实现复杂度。
缺点：1. 需要较好的设计。
注意事项：根据具体的应用场景在选择确认该设计模式，否则会增加系统的复杂度。

实现

我们将创建一个Person对象、Criteria接口和实现了该接口的实体类，来过滤Person对象的列表。CriteriaPatternDemo，我们的演示类使用Criteria对象，基于各种标准和它们的结合来过滤Person对象的列表。

步骤 1

创建一个类，在该类上应用标准。
Person.java

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;   }    }

步骤 2

为标准（Criteria）创建一个接口。
Criteria.java

import java.util.List;public interface Criteria {   public List<Person> meetCriteria(List<Person> persons);}

步骤 3

创建实现了Criteria接口的实体类。
CriteriaMale.java

import java.util.ArrayList;import java.util.List;public class CriteriaMale implements Criteria {   @Override   public List<Person> meetCriteria(List<Person> persons) {      List<Person> malePersons = new ArrayList<Person>();       for (Person person : persons) {         if(person.getGender().equalsIgnoreCase("MALE")){            malePersons.add(person);         }      }      return malePersons;   }}

CriteriaFemale.java

import java.util.ArrayList;import java.util.List;public class CriteriaFemale implements Criteria {   @Override   public List<Person> meetCriteria(List<Person> persons) {      List<Person> femalePersons = new ArrayList<Person>();       for (Person person : persons) {         if(person.getGender().equalsIgnoreCase("FEMALE")){            femalePersons.add(person);         }      }      return femalePersons;   }}

CriteriaSingle.java

import java.util.ArrayList;import java.util.List;public class CriteriaSingle implements Criteria {   @Override   public List<Person> meetCriteria(List<Person> persons) {      List<Person> singlePersons = new ArrayList<Person>();       for (Person person : persons) {         if(person.getMaritalStatus().equalsIgnoreCase("SINGLE")){            singlePersons.add(person);         }      }      return singlePersons;   }}

AndCriteria.java

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> firstCriteriaPersons = criteria.meetCriteria(persons);             return otherCriteria.meetCriteria(firstCriteriaPersons);   }}

OrCriteria.java

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> firstCriteriaItems = criteria.meetCriteria(persons);      List<Person> otherCriteriaItems = otherCriteria.meetCriteria(persons);      for (Person person : otherCriteriaItems) {         if(!firstCriteriaItems.contains(person)){            firstCriteriaItems.add(person);         }      }       return firstCriteriaItems;   }}

步骤 4

使用不同的标准（Criteria）和它们的结合来过滤Person对象的列表。
CriteriaPatternDemo.java

import java.util.ArrayList; import java.util.List;public class CriteriaPatternDemo {   public static void main(String[] args) {      List<Person> persons = new ArrayList<Person>();      persons.add(new Person("Robert","Male", "Single"));      persons.add(new Person("John","Male", "Married"));      persons.add(new Person("Laura","Female", "Married"));      persons.add(new Person("Diana","Female", "Single"));      persons.add(new Person("Mike","Male", "Single"));      persons.add(new Person("Bobby","Male", "Single"));      Criteria male = new CriteriaMale();      Criteria female = new CriteriaFemale();      Criteria single = new CriteriaSingle();      Criteria singleMale = new AndCriteria(single, male);      Criteria singleOrFemale = new OrCriteria(single, female);      System.out.println("Males: ");      printPersons(male.meetCriteria(persons));      System.out.println("\nFemales: ");      printPersons(female.meetCriteria(persons));      System.out.println("\nSingle Males: ");      printPersons(singleMale.meetCriteria(persons));      System.out.println("\nSingle Or Females: ");      printPersons(singleOrFemale.meetCriteria(persons));   }   public static void printPersons(List<Person> persons){      for (Person person : persons) {         System.out.println("Person : [ Name : " + person.getName()             +", Gender : " + person.getGender()             +", Marital Status : " + person.getMaritalStatus()            +" ]");      }   }      }

步骤 5

验证输出。

Males: Person : [ Name : Robert, Gender : Male, Marital Status : Single ]Person : [ Name : John, Gender : Male, Marital Status : Married ]Person : [ Name : Mike, Gender : Male, Marital Status : Single ]Person : [ Name : Bobby, Gender : Male, Marital Status : Single ]Females: Person : [ Name : Laura, Gender : Female, Marital Status : Married ]Person : [ Name : Diana, Gender : Female, Marital Status : Single ]Single Males: Person : [ Name : Robert, Gender : Male, Marital Status : Single ]Person : [ Name : Mike, Gender : Male, Marital Status : Single ]Person : [ Name : Bobby, Gender : Male, Marital Status : Single ]Single Or Females: Person : [ Name : Robert, Gender : Male, Marital Status : Single ]Person : [ Name : Diana, Gender : Female, Marital Status : Single ]Person : [ Name : Mike, Gender : Male, Marital Status : Single ]Person : [ Name : Bobby, Gender : Male, Marital Status : Single ]Person : [ Name : Laura, Gender : Female, Marital Status : Married ]