介绍

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

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

步骤 3

创建实现了

Criteria 接口的实体类。

CriteriaMale.java

public class CriteriaMale implements Criteria {    @Override    public List<Person> meetCriteria(List<Person> persons) {        List<Person> malePersons = new ArrayList<>();        for (Person person : persons) {            if (person.getGender().equalsIgnoreCase("Male")) {                malePersons.add(person);            }        }        return malePersons;    }    }

CriteriaFemale.java

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

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

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> list = criteria.meetCriteria(persons);        return otherCriteria.meetCriteria(list);    }}

OrCriteria.java

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> first = criteria.meetCriteria(persons);        List<Person> other = otherCriteria.meetCriteria(persons);        for (Person person : other) {            if (!first.contains(person)) {                first.add(person);            }        }        return first;    }}

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 ]