前言
目前设计模式学习主要基于菜鸟教程的设计模式，后期不排除会追加从其他地方学来内容。 文章最后“Java设计模式笔记示例代码整合”为本系列代码整合，所有代码均为个人手打并运行测试，不定期更新。本节内容位于其Filter包（package）中。 
过滤器模式
过滤器模式（Filter Pattern）或标准模式（Criteria Pattern）是一种设计模式，这种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它们连接起来。这种类型的设计模式属于结构型模式，它结合多个标准来获得单一标准。
具体实现
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。
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; }
}2、为标准（Criteria）创建一个接口。
public interface Criteria { public List<Person> meetCriteria(List<Person> persions);}3、创建实现了 Criteria 接口的实体类。
CriteriaMale.java
public class CriteriaMale implements Criteria{ public List<Person> meetCriteria(List<Person> persons) { List<Person> melePersons = new ArrayList<Person>(); for(Person person:persons){ if (person.getGender().equalsIgnoreCase("MALE")){ melePersons.add(person); } } return melePersons; }}CriteriaFemale.java
public class CriteriaFemal implements Criteria { 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
public class CriteraSingle implements Criteria { 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
public class AndCriteria implements Criteria { private Criteria criteria; private Criteria otherCriteria;
public AndCriteria(Criteria criteria,Criteria otherCriteria){ this.criteria =criteria; this.otherCriteria = otherCriteria; } public List<Person> meetCriteria(List<Person> persions) { List<Person> firstCriteriaPersons = criteria.meetCriteria(persions); return otherCriteria.meetCriteria(firstCriteriaPersons); }}OrCriteria.java
public class OrCriteria implements Criteria { private Criteria criteria; private Criteria otherCriteria;
public OrCriteria(Criteria criteria,Criteria otherCriteria){ this.criteria = criteria; this.otherCriteria = otherCriteria; }
public List<Person> meetCriteria(List<Person> persions) { List<Person> firstCriteriaItems = criteria.meetCriteria(persions); List<Person> otherCriteriaItems = otherCriteria.meetCriteria(persions); 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。
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 CriteriaFemal(); Criteria single = new CriteraSingle(); Criteria singleMale = new AndCriteria(single,male); Criteria singleOrFemale = new OrCriteria(single,female);
System.out.println("Males: "); printPersons(male.meetCriteria(persons));
System.out.println("\nFemale: "); 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() +" ]"); } }}5、验证输出。
[callout class=“info” title=""] 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 ] Female: 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 ] [/callout]
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