過濾器模式是指通過構造一系列不同的標準實現類，通過這些標準實現類把目標對象（通常是多個）按照對應的標準進行過濾，從而得到想要的對象（或對象組）。這些標準實現類也可以構造成多個標準組合的形式（多個標準的“與”、“或”、“非”結合）。

下例中以過濾人員對象為例，人員Person類具有name、gender、maritalStatus等3個屬性，在主函數中構造一組人員，使各人員具有不同的屬性，然后通過過濾器對這些人員進行過濾。類圖如下：

Person類：

package filter;
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;
  }
  public String getInformation() {
    return name+":"+gender+","+maritalStatus;
  }
}

Criteria接口類：

package filter;
import java.util.List;
public interface Criteria {
  List < Person > meetCriteria(List < Person > persons);
}

CriteriaFemale實現類：

package filter;
import java.util.ArrayList;
import java.util.List;
/*
 * 過濾得到女性人員
 */
public class CriteriaFemale implements Criteria{
  @Override
  public List< Person > meetCriteria(List< Person > persons) {
    List < Person > femalePerson = new ArrayList < Person >();
    for(Person person: persons) {
      if(person.getGender().equals("女")) {
        femalePerson.add(person);
      }
    }
    return femalePerson;
  }
}

CriteriaMale實現類：

package filter;
import java.util.ArrayList;
import java.util.List;
/*
 * 過濾得到男性人員
 */
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().equals("男")) {
        malePersons.add(person);
      }
    }
    return malePersons;
  }
}

CriteriaSingle實現類：

package filter;
import java.util.ArrayList;
import java.util.List;
/*
 * 過濾得到單身人員
 */
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().equals("單身")) {
        singlePersons.add(person);
      }
    }
    return singlePersons;
  }
}

Andcriteria實現類：

package filter;
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實現類：

package filter;
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 > firstCriteriaPersons = criteria.meetCriteria(persons);
    List< Person > ohterCriteriaPersons = otherCriteria.meetCriteria(persons);
    for(Person person: ohterCriteriaPersons) {
      if(!firstCriteriaPersons.contains(person)) {
        firstCriteriaPersons.add(person);
      }
    }
    return firstCriteriaPersons;
  }
}

主函數調用類：

package main;
import java.util.ArrayList;
import java.util.List;
import filter.*;
public class FilterPattern {
  public static void main(String[] args) {
    List < Person > persons=new ArrayList < Person > ();
    persons.add(new Person("張三","男","單身"));
    persons.add(new Person("李四","女","已婚"));
    persons.add(new Person("王五","女","單身"));
    persons.add(new Person("趙六","男","已婚"));
    persons.add(new Person("張七","女","單身"));
    persons.add(new Person("李八","男","單身"));
    persons.add(new Person("王九","女","單身"));
    //過濾得到男性
    Criteria male= new CriteriaMale();
    List < Person > malePersons=male.meetCriteria(persons);
    System.out.println("全部男性：");
    for(Person person: malePersons) {
      System.out.println(person.getInformation());
    }
    //過濾得到女性
    Criteria female = new CriteriaFemale();
    List < Person > femalePersons=female.meetCriteria(persons);
    System.out.println("全部女性：");
    for(Person person: femalePersons) {
      System.out.println(person.getInformation());
    }
    //過濾得到單身人士
    Criteria single = new CriteriaSingle();
    List < Person > singlePersons=single.meetCriteria(persons);
    System.out.println("全部單身：");
    for(Person person: singlePersons) {
      System.out.println(person.getInformation());
    }
    //過濾得到單身女性
    Criteria femaleSingle = new AndCriteria(female,single);
    List < Person > femaleSinglePersons=femaleSingle.meetCriteria(persons);
    System.out.println("全部單身女性：");
    for(Person person: femaleSinglePersons) {
      System.out.println(person.getInformation());
    }
    //過濾得到男性或單身人士
    Criteria maleOrSingle = new OrCriteria(male,single);
    List < Person > maleOrSinglePersons=maleOrSingle.meetCriteria(persons);
    System.out.println("全部單身或男性：");
    for(Person person: maleOrSinglePersons) {
      System.out.println(person.getInformation());
    }
  }
}