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

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

    //Criteria.java
    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
    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;
       }
    }

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()
                +" ]");
          }
       }
    }