基本概念
过滤器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的模式,它可以组合多个标准来获得单一的标准。
结构图
上图摘自http://www.tutorialspoint.com/design_pattern
应用场景
当你有一组对象,需要通过不同条件或条件组合来筛选出符合标准的结果时,可以使用过滤器模式。
源码示例(代码案例来自http://www.tutorialspoint.com/design_pattern)
1.先创建要过滤的目标对象Person类
package com.spook.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; } }2.创建一个通用标准接口Criteria
package com.spook.filter; import java.util.List; /** * 通用标准接口 */ public interface Criteria { public List<Person> meetCriteria(List<Person> persons); }3.创建一个标准实现类
package com.spook.filter; import java.util.ArrayList; import java.util.List; /** * 标准实现类,过滤为男性的Person */ public class CriteriaMale implements Criteria { @Override public List<Person> meetCriteria(List<Person> persons) { // TODO Auto-generated method stub List<Person> malePersons = new ArrayList<Person>(); for (Person person : persons) { if ("male".equalsIgnoreCase(person.getGender())) { malePersons.add(person); } } return malePersons; } }4.创建另一个标准实现类
package com.spook.filter; import java.util.ArrayList; import java.util.List; /** * 标准实现类,过滤为女性的Person */ public class CriteriaFemale implements Criteria { @Override public List<Person> meetCriteria(List<Person> persons) { // TODO Auto-generated method stub List<Person> femalePersons = new ArrayList<Person>(); for (Person person : persons) { if ("female".equalsIgnoreCase(person.getGender())) { femalePersons.add(person); } } return femalePersons; } }5.标准实现类
package com.spook.filter; import java.util.ArrayList; import java.util.List; /** * 标准实现类,过滤为单身的Person */ public class CriteriaSingle implements Criteria { @Override public List<Person> meetCriteria(List<Person> persons) { // TODO Auto-generated method stub List<Person> singlePersons = new ArrayList<Person>(); for (Person person : persons) { if ("single".equalsIgnoreCase(person.getMaritalStatus())) { singlePersons.add(person); } } return singlePersons; } }6.组合标准,需同时符合两个条件的过滤
package com.spook.filter; import java.util.List; /** * 组合标准实现类,需同时满足 */ 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) { // TODO Auto-generated method stub List<Person> firstCriteriaPersons = criteria.meetCriteria(persons); return otherCriteria.meetCriteria(firstCriteriaPersons); } }7.组合标准,满足任何一个即可
package com.spook.filter; import java.util.List; /** * 组合标准实现类,满足其一即可 */ 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) { // TODO Auto-generated method stub List<Person> firstCriteriaPersons = criteria.meetCriteria(persons); List<Person> otherCriteriaPersons = otherCriteria.meetCriteria(persons); for (Person person : otherCriteriaPersons) { if (!firstCriteriaPersons.contains(person)) { firstCriteriaPersons.add(person); } } return firstCriteriaPersons; } }8.测试类
package com.spook.filter; import java.util.ArrayList; import java.util.List; /** * 测试类 */ public class Test { public static void main(String[] args) { // TODO Auto-generated method stub 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() + " ]"); } } }运行测试类输出如下内容:
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 ]