十二、过滤器模式 ( Filter Pattern )

过滤器模式（Filter Pattern）或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

过滤器模式（Filter Pattern） 又称 标准模式（Criteria Pattern）

过滤器模式属于结构型模式，它结合多个标准来获得单一标准

实现

1、 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
2、 CriteriaPatternDemo 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

范例

1、 创建一个类，在该类上应用标准

Person.java

// author: 大白菜(www.cmsblogs.cn)
// Copyright © 2015-2065 www.cmsblogs.cn. All rights reserved.

package cn.cmsblogs.gof;

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;
   }    
}

2、 为标准（Criteria）创建一个接口

Criteria.java

// author: 大白菜(www.cmsblogs.cn)
// Copyright © 2015-2065 www.cmsblogs.cn. All rights reserved.

package cn.cmsblogs.gof;

import java.util.List;

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

3、 创建实现了 Criteria 接口的实体类

CriteriaMale.java

// author: 大白菜(www.cmsblogs.cn)
// Copyright © 2015-2065 www.cmsblogs.cn. All rights reserved.

package cn.cmsblogs.gof;

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

// author: 大白菜(www.cmsblogs.cn)
// Copyright © 2015-2065 www.cmsblogs.cn. All rights reserved.

package cn.cmsblogs.gof;

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

// author: 大白菜(www.cmsblogs.cn)
// Copyright © 2015-2065 www.cmsblogs.cn. All rights reserved.

package cn.cmsblogs.gof;

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

// author: 大白菜(www.cmsblogs.cn)
// Copyright © 2015-2065 www.cmsblogs.cn. All rights reserved.

package cn.cmsblogs.gof;

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

// author: 大白菜(www.cmsblogs.cn)
// Copyright © 2015-2065 www.cmsblogs.cn. All rights reserved.

package cn.cmsblogs.gof;

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;
   }
}

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

// author: 大白菜(www.cmsblogs.cn)
// Copyright © 2015-2065 www.cmsblogs.cn. All rights reserved.

package cn.cmsblogs.gof;

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()
            +" ]");
      }
   }      
}

编译运行以上 Java 范例，输出结果如下

$ javac -d . src/main/cn/cmsblogs/gof/CriteriaPatternDemo.java
$ java  cn.cmsblogs.gof.CriteriaPatternDemo
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 ]