08-Java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

package com.demo.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

package com.demo.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

package com.demo.gof;
import java.util.ArrayList;
import java.util.List;public class CriteriaMale implements Criteria {@Overridepublic 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

package com.demo.gof;
import java.util.ArrayList;
import java.util.List;public class CriteriaFemale implements Criteria {@Overridepublic 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

package com.demo.gof;
import java.util.ArrayList;
import java.util.List;public class CriteriaSingle implements Criteria {@Overridepublic 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

package com.demo.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; }@Overridepublic List<Person> meetCriteria(List<Person> persons) {List<Person> firstCriteriaPersons = criteria.meetCriteria(persons);       return otherCriteria.meetCriteria(firstCriteriaPersons);}

OrCriteria.java

package com.demo.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; }@Overridepublic 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

package com.demo.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/com.demo/gof/CriteriaPatternDemo.java
$ java  com.demo.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 ]