Java特性之设计模式【过滤器模式】

一、过滤器模式

概述

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

主要解决：在众多数据中，根据特定的标准，在一组数据中筛选出不同标准的数据

优缺点

优点：

将对象的过滤、校验逻辑抽离出来，降低系统的复杂度
过滤规则可实现重复利用

缺点：

性能较低，每个过滤器对每一个元素都会进行遍历。如果有n个元素，m个过滤器，则时间复杂度为O(mn)

1. 各个角色介绍

1.1 过滤器接口（Filter）

定义了过滤器的基本方法，具体的实现还要具体过滤器角色去参与，在实际应用中可以扩展该接口以适应不同的过滤条件

1.2 具体命过滤器（ConcreteFilter）

实现了过滤器接口，负责执行具体的过滤操作。对数据进行过滤

1.3 过滤链（FilterChain）

将多个过滤器按照一定的顺序组合起来，形成一个过滤器链，依次对数据进行过滤

2. UML图

首先创建一个 Shape 对象，作为过滤的接口 IFilter，然后实现该接口，创建对应的 CornerFilter、CurveFilter、EdgeFilter具体过滤器。然后创建带有过滤器的过滤链 FilterChain，基于各种标准和它们的结合来过滤 Shape 对象的列表

在这里插入图片描述

3. 具体例子和代码

角色分配

Shape：形状
IFilter：过滤器接口
- CornerFilter：角过滤器（实现过滤器接口）
- EdgeFilter：边过滤器（实现过滤器接口）
- CurveFilter：曲线过滤器（实现过滤器接口）
FilterChain：过滤链

3.1 形状

Instruction

package com.vinjcent.prototype.filter;import io.swagger.annotations.ApiModelProperty;/*** @author vinjcent* @description 形状*/
public class Shape {@ApiModelProperty("形状名称")private String name;@ApiModelProperty("是否有角")private Boolean isCorner;@ApiModelProperty("边数")private Integer edges;@ApiModelProperty("线构成类型")private String type;public Shape(String name, Boolean isCorner, Integer edges, String type) {this.name = name;this.isCorner = isCorner;this.edges = edges;this.type = type;}public String getName() {return name;}public void setName(String name) {this.name = name;}public Boolean getCorner() {return isCorner;}public void setCorner(Boolean corner) {isCorner = corner;}public Integer getEdges() {return edges;}public void setEdges(Integer edges) {this.edges = edges;}public String getType() {return type;}public void setType(String type) {this.type = type;}
}

3.2 过滤接口及其实现类

IFilter

package com.vinjcent.prototype.filter;import java.util.List;/*** @author vinjcent* @description 过滤接口*/
public interface IFilter {/*** 适配标准形状** @param shapes 形状列表* @return 适配的形状列表*/List<Shape> adaptFilter(List<Shape> shapes);
}

CornerFilter

package com.vinjcent.prototype.filter;import java.util.ArrayList;
import java.util.List;/*** @author vinjcent* /* @description 角过滤器*/
public class CornerFilter implements IFilter {@Overridepublic List<Shape> adaptFilter(List<Shape> shapes) {// 符合具有角的形状List<Shape> cornerFilter = new ArrayList<>();for (Shape shape : shapes) {if (shape.getIsCorner()) {cornerFilter.add(shape);}}return cornerFilter;}}

EdgeFilter

package com.vinjcent.prototype.filter;import java.util.ArrayList;
import java.util.List;/*** @author vinjcent* /* @description 边过滤器*/
public class EdgeFilter implements IFilter {@Overridepublic List<Shape> adaptFilter(List<Shape> shapes) {// 边数大于0的形状List<Shape> edgeFilter = new ArrayList<>();for (Shape shape : shapes) {if (shape.getEdges() > 0) {edgeFilter.add(shape);}}return edgeFilter;}}

CurveFilter

package com.vinjcent.prototype.filter;import java.util.ArrayList;
import java.util.List;/*** @author vinjcent* /* @description 曲线过滤器*/
public class CurveFilter implements IFilter {@Overridepublic List<Shape> adaptFilter(List<Shape> shapes) {// 曲线List<Shape> curveFilter = new ArrayList<>();for (Shape shape : shapes) {if (shape.getType().toLowerCase().contains("curve")) {curveFilter.add(shape);}}return curveFilter;}}

3.3 过滤链

FilterChain

package com.vinjcent.prototype.filter;import com.vinjcent.api.utils.CollectionUtils;
import io.swagger.annotations.ApiModelProperty;
import lombok.Data;import java.util.ArrayList;
import java.util.List;/*** @author vinjcent* @description 过滤链*/
@Data
public class FilterChain {@ApiModelProperty("过滤器集合")private List<IFilter> filters;public FilterChain(List<IFilter> filters) {this.filters = filters;}public List<Shape> doFilter(List<Shape> shapes) {if (CollectionUtils.isEmpty(filters) || CollectionUtils.isEmpty(shapes)) {return new ArrayList<>();}List<Shape> afterFilterShapes = new ArrayList<>(shapes);// 执行过滤for (IFilter filter : filters) {afterFilterShapes = filter.adaptFilter(afterFilterShapes);}return afterFilterShapes;}
}

3.4 测试主函数

package com.vinjcent.prototype.filter;import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;/*** @author vinjcent* 过滤模式*/
public class Main {public static void main(String[] args) {List<Shape> shapes = new ArrayList<>();shapes.add(new Shape("Circle", false, 0, "Curve"));shapes.add(new Shape("Triangle", true, 3, "Straight"));shapes.add(new Shape("Rectangle", true, 4, "Straight"));shapes.add(new Shape("Square", true, 4, "Straight"));shapes.add(new Shape("Oval", false, 0, "Curve"));shapes.add(new Shape("Sector", true, 2, "Curve and Straight"));CornerFilter cornerFilter = new CornerFilter();EdgeFilter edgeFilter = new EdgeFilter();CurveFilter curveFilter = new CurveFilter();// 具有角、边的形状FilterChain cornerAndEdgeFilterChain = new FilterChain(Arrays.asList(cornerFilter, edgeFilter));List<Shape> cornerAndEdgeShapes = cornerAndEdgeFilterChain.doFilter(shapes);System.out.println("具有角、边的形状:");printResult(cornerAndEdgeShapes);// 具有角、曲线的形状FilterChain cornerAndCurveFilterChain = new FilterChain(Arrays.asList(cornerFilter, curveFilter));List<Shape> cornerAndCurveShapes = cornerAndCurveFilterChain.doFilter(shapes);System.out.println("\n具有角、曲线的形状:");printResult(cornerAndCurveShapes);// 具有边、曲线的形状FilterChain edgeAndCurveFilterChain = new FilterChain(Arrays.asList(edgeFilter, curveFilter));List<Shape> edgeAndCurveShapes = edgeAndCurveFilterChain.doFilter(shapes);System.out.println("\n具有边、曲线的形状:");printResult(edgeAndCurveShapes);}public static void printResult(List<Shape> shapes) {for (Shape shape : shapes) {System.out.println("Shape{" +"name='" + shape.getName() + '\'' +", isCorner=" + shape.getIsCorner() +", edges=" + shape.getEdges() +", type='" + shape.getType() + '\'' +'}');}}}