过滤器模式-Filter Pattern

最新推荐文章于 2024-06-26 06:19:58 发布

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#设计模式 #过滤器模式

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本文介绍了一种设计模式——过滤器模式，它允许开发者通过多种标准筛选对象集合，并以解耦方式将这些标准逻辑组合。文章提供了详细的代码示例，展示了如何实现及应用此模式。

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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 ]