Java设计模式学习笔记—过滤器模式
前言
目前设计模式学习主要基于菜鸟教程的设计模式，后期不排除会追加从其他地方学来内容。 文章最后“Java设计模式笔记示例代码整合”为本系列代码整合，所有代码均为个人手打并运行测试，不定期更新。本节内容位于其Filter包（package）中。 
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。
具体实现
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。
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;
}
}
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2、为标准（Criteria）创建一个接口。
public interface Criteria {
public List<Person> meetCriteria(List<Person> persions);
}
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3、创建实现了 Criteria 接口的实体类。
CriteriaMale.java
public class CriteriaMale implements Criteria{
public List<Person> meetCriteria(List<Person> persons) {
List<Person> melePersons = new ArrayList<Person>();
for(Person person:persons){
if (person.getGender().equalsIgnoreCase("MALE")){
melePersons.add(person);
}
}
return melePersons;
}
}
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CriteriaFemale.java
public class CriteriaFemal implements Criteria {
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;
}
}
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CriteriaSingle.java
public class CriteraSingle implements Criteria {
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;
}
}
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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;
}
public List<Person> meetCriteria(List<Person> persions) {
List<Person> firstCriteriaPersons = criteria.meetCriteria(persions);
return otherCriteria.meetCriteria(firstCriteriaPersons);
}
}
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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;
}
public List<Person> meetCriteria(List<Person> persions) {
List<Person> firstCriteriaItems = criteria.meetCriteria(persions);
List<Person> otherCriteriaItems = otherCriteria.meetCriteria(persions);
for (Person person : otherCriteriaItems){
if (!firstCriteriaItems.contains(person)){
firstCriteriaItems.add(person);
}
}
return firstCriteriaItems;
}
}
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4、使用不同的标准（Criteria）和它们的结合来过滤 Person 对象的列表。
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 CriteriaFemal();
Criteria single = new CriteraSingle();
Criteria singleMale = new AndCriteria(single,male);
Criteria singleOrFemale = new OrCriteria(single,female);
System.out.println("Males: ");
printPersons(male.meetCriteria(persons));
System.out.println("\nFemale: ");
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()
+" ]");
}
}
}
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5、验证输出。
[callout class=“info” title=“”] 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 ] Female: 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 ] [/callout]
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