菜鸟学设计模式----过滤器模式

过滤器模式或者说是标准模式是一种设计模式，它允许开发人员使用不同标准去过滤同一组对象，通过逻辑运算，以解耦的方式将它们连接起来。这种类型的设计模式属于结构型模式，它结合 多个标准来获取单一标准。

实现

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。

第一步：创建一个类，在该类上应用标准

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;   }    }

第二步：为标准创建一个接口

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

第三步：创建实现了 Criteria 接口的实体类

1. CriteriaMale

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;   }}

1. CriteriaFemale

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;   }}

1. CriteriaSingle

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;   }}

1. AndCriteria

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);   }}

1. OrCriteria

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;   }}

第四步：使用不同的标准和它们的结合来过滤Person对象的列表

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;   }}

第四步：使用不同的标准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 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()            +" ]");      }   }      }

第五步：验证输出结果

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 ]

从输出结果来看，根据不同的过滤条件，成功过滤出了males、females、single males、single or females。在这里，只是先了解一下过滤器模式的思想，在真实场景使用过滤器模式的话，往往要复杂的多。