设计模式第9篇：过滤器模式

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。

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

  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 ]

作者：jarodhu

来源：https://www.w3cschool.cn/shejimoshi/filter-pattern.html