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 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。

过滤器模式的 UML 图

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

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 ( " \n Females: " ) ; printPersons ( female . meetCriteria ( persons ) ) ; System . out . println ( " \n Single Males: " ) ; printPersons ( singleMale . meetCriteria ( persons ) ) ; System . out . println ( " \n Single 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

执行程序，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 ]