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 ]