1、概述
生成器模式是一种创建型设计模式, 使你能够分步骤创建复杂对象。 该模式允许你使用相同的创建代码生成不同类型和形式的对象。
2、适用场景
1)避免重叠构造函数,例如:一个类有很多的属性,这时候的构造方法需要传递很多的参数,为了避免这样,会重新写一个相对参数较少的构造方法,但是仍然需要对其他参数进行赋默认值。
2)当需要创建不同的产品类型,此处指比较接近的产品类型,则可以在顶层builder中包含大部分产品属性的赋值方法。
3、实例
有以下场景,我们分别使用常规方式和建造者模式实现:
当前有一个汽车工厂,可以生产的汽车类型有city,sport。
除了汽车之外,同样可以生产汽车的相关手册manual。
汽车有以下的属性:
1、type 类型
2、seats 座位数
3、engine 引擎
4、GPS 导航
分别实现汽车和手册的生产过程
3.1 不适用建造者模式
分别创建车car和手册manual,以及其内部的属性,当前例子中车和手册是相同的属性。
import lombok.Data;
/**
* TODO
* @date: 2021/1/4
* @author weirx
* @version 3.0
*/
@Data
public class Car {
private CarType type;
private int seats;
private Engine engine;
private GPS GPS;
public Car(CarType type, int seats, Engine engine, com.cloud.bssp.designpatterns.builder.withouttdesign.entity.GPS GPS) {
this.type = type;
this.seats = seats;
this.engine = engine;
this.GPS = GPS;
}
public void detail() {
System.out.println("this is " + type + " car");
System.out.println("the seats is :" + seats);
System.out.println("the engine is :" + engine);
System.out.println("this GPS is :" + GPS);
}
}
import lombok.Data;
/**
* TODO
* @date: 2021/1/4
* @author weirx
* @version 3.0
*/
@Data
public class Manual {
private CarType type;
private int seats;
private Engine engine;
private GPS GPS;
public Manual(CarType type, int seats, Engine engine, com.cloud.bssp.designpatterns.builder.withouttdesign.entity.GPS GPS) {
this.type = type;
this.seats = seats;
this.engine = engine;
this.GPS = GPS;
}
public void detail() {
System.out.println("this is " + type + " car");
System.out.println("the seats is :" + seats);
System.out.println("the engine is :" + engine);
System.out.println("this GPS is :" + GPS);
}
}
/**
* TODO
* @date: 2021/1/4
* @author weirx
* @version 3.0
*/
public enum CarType {
SPORT,CITY;
}
import lombok.Data;
/**
* 汽车引擎
* @date: 2021/1/4
* @author weirx
* @version 3.0
*/
@Data
public class Engine {
/**
* 排量
*/
private final double volume;
/**
* 里程
*/
private double mileage;
public Engine(double volume, double mileage) {
this.volume = volume;
this.mileage = mileage;
}
}
import lombok.Data;
/**
* TODO
* @date: 2021/1/4
* @author weirx
* @version 3.0
*/
@Data
public class GPS {
/**
* 路线
*/
private String route;
public GPS(String route) {
this.route = route;
}
}
测试类:
import com.cloud.bssp.BsspUserApplication;
import com.cloud.bssp.designpatterns.builder.withouttdesign.entity.*;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.test.context.junit4.SpringRunner;
/**
* 客户端
* @date: 2021/1/4
* @author weirx
* @version 3.0
*/
@RunWith(SpringRunner.class)
@SpringBootTest(classes = BsspUserApplication.class)
public class TestDemo {
@Test
public void test() {
//生产运动汽车
Car sportCar = new Car(
CarType.SPORT,
2,
new Engine(3.0, 0),
new GPS("haerbin nangang haerbindajie")
);
sportCar.detail();
System.out.println("----------------------------------------");
//生产城市汽车
Car cityCar = new Car(
CarType.CITY,
4,
new Engine(2.0, 0),
new GPS("haerbin nangang haerbindajie")
);
cityCar.detail();
System.out.println("----------------------------------------");
//生产汽车手册
Manual manual = new Manual(
CarType.CITY,
4,
new Engine(2.0, 0),
new GPS("haerbin nangang haerbindajie")
);
manual.detail();
System.out.println("----------------------------------------");
}
}
结果:
this is SPORT car
the seats is :2
the engine is :Engine(volume=3.0, mileage=0.0)
this GPS is :GPS(route=haerbin nangang haerbindajie)
----------------------------------------
this is CITY car
the seats is :4
the engine is :Engine(volume=2.0, mileage=0.0)
this GPS is :GPS(route=haerbin nangang haerbindajie)
----------------------------------------
this is CITY car
the seats is :4
the engine is :Engine(volume=2.0, mileage=0.0)
this GPS is :GPS(route=haerbin nangang haerbindajie)
----------------------------------------
3.2 建造者实现
使用建造者模式后,代码要比上面的方法多了不少:
创建顶层Builder
import com.cloud.bssp.designpatterns.builder.usedesign.entity.CarType;
import com.cloud.bssp.designpatterns.builder.usedesign.entity.Engine;
import com.cloud.bssp.designpatterns.builder.usedesign.entity.GPS;
/**
* TODO
* @date: 2021/1/4
* @author weirx
* @version 3.0
*/
public interface Builder {
void setCarType(CarType carType);
void setSeats(int seats);
void setEngine(Engine engine);
void setGPS(GPS gps);
}
创建实体类,与3.1中是相同的,这里不重复粘贴了。
创建car的builder:
import com.cloud.bssp.designpatterns.builder.usedesign.entity.Car;
import com.cloud.bssp.designpatterns.builder.usedesign.entity.CarType;
import com.cloud.bssp.designpatterns.builder.usedesign.entity.Engine;
import com.cloud.bssp.designpatterns.builder.usedesign.entity.GPS;
import lombok.Data;
/**
* TODO
* @date: 2021/1/4
* @author weirx
* @version 3.0
*/
@Data
public class CarBuilder implements Builder {
private CarType carType;
private int seats;
private Engine engine;
private GPS GPS;
public Car getResult() {
return new Car(carType, seats, engine, GPS);
}
}
创建手册builder:
import com.cloud.bssp.designpatterns.builder.usedesign.entity.*;
import lombok.Data;
/**
* TODO
* @date: 2021/1/4
* @author weirx
* @version 3.0
*/
@Data
public class ManualBuilder implements Builder {
private CarType carType;
private int seats;
private Engine engine;
private GPS GPS;
public Manual getResult() {
return new Manual(carType, seats, engine, GPS);
}
}
创建一个builder管理器:
import com.cloud.bssp.designpatterns.builder.usedesign.builder.Builder;
import com.cloud.bssp.designpatterns.builder.usedesign.entity.CarType;
import com.cloud.bssp.designpatterns.builder.usedesign.entity.Engine;
import com.cloud.bssp.designpatterns.builder.usedesign.entity.GPS;
/**
* TODO
* @date: 2021/1/4
* @author weirx
* @version 3.0
*/
public class Director {
public void constructSportsCar(Builder builder) {
builder.setCarType(CarType.SPORT);
builder.setSeats(2);
builder.setEngine(new Engine(3.0, 0));
builder.setGPS(new GPS("haerbin nangang haerbindajie"));
}
public void constructCityCar(Builder builder) {
builder.setCarType(CarType.CITY);
builder.setSeats(4);
builder.setEngine(new Engine(2.0, 0));
builder.setGPS(new GPS("haerbin nangang haerbindajie"));
}
}
测试类:
import com.cloud.bssp.BsspUserApplication;
import com.cloud.bssp.designpatterns.builder.usedesign.builder.CarBuilder;
import com.cloud.bssp.designpatterns.builder.usedesign.builder.ManualBuilder;
import com.cloud.bssp.designpatterns.builder.usedesign.director.Director;
import com.cloud.bssp.designpatterns.builder.usedesign.entity.Car;
import com.cloud.bssp.designpatterns.builder.usedesign.entity.Manual;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.test.context.junit4.SpringRunner;
/**
* 客户端
* @date: 2021/1/4
* @author weirx
* @version 3.0
*/
@RunWith(SpringRunner.class)
@SpringBootTest(classes = BsspUserApplication.class)
public class TestDemo {
@Test
public void test() {
Director director = new Director();
//生产运动汽车
CarBuilder carBuilder = new CarBuilder();
director.constructSportsCar(carBuilder);
Car sportCar = carBuilder.getResult();
sportCar.detail();
System.out.println("-----------------------------------");
//生产城市汽车
director.constructCityCar(carBuilder);
Car cityCar = carBuilder.getResult();
cityCar.detail();
System.out.println("-----------------------------------");
//生产汽车手册
ManualBuilder manualBuilder = new ManualBuilder();
director.constructCityCar(manualBuilder);
Manual manual = manualBuilder.getResult();
manual.detail();
System.out.println("-----------------------------------");
}
}
结果:
this is SPORT car
the seats is :2
the engine is :Engine(volume=3.0, mileage=0.0)
this GPS is :GPS(route=haerbin nangang haerbindajie)
-----------------------------------
this is CITY car
the seats is :4
the engine is :Engine(volume=2.0, mileage=0.0)
this GPS is :GPS(route=haerbin nangang haerbindajie)
-----------------------------------
this Manual CITY car
the Manual seats is :4
the Manual engine is :Engine(volume=2.0, mileage=0.0)
this GManual PS is :GPS(route=haerbin nangang haerbindajie)
-----------------------------------
4、分析
建造者模式基本有以下几个角色:
如上面两种方式的结果显示,都可以实现生产汽车和手册。
结果没什么差异。
在没使用建造者的方式中:生产汽车的参数是由客户端自己指定的,并且需要传很多的参数,实际工作中可能需要更多的参数,可能有部分参数是不需要的。
使用建造者模式,用户不需要去具体指定多个参数了,对于客户端更友好。
builder:将产品new()提出到builder中,提供产品所拥有的属性设置方法,一类产品都可以使用这个builder进行产品创建。
director:作为builder的管理者,主要控制产品的属性设置,在这个类中,具体指定除了可以生产的产品的构造,并且对属性进行赋值,最终返回一个用户需要的builder。
客户端调用只需要创建需要的产品类型builder,通过管理者director对builder进行属性设置,最终客户端通过调用builder的方法获取最终需要的产品。
极大程度减少并优化的客户端的代码,同时由管理者director限制了产品的种类。
从扩展层层面看:
未使用建造者:增加对应的产品类,客户端直接new。
建造者模式:增加builder,并且在director增加可创建的产品的builder构造。
5、总结
优点:
1)遵守单一原则。
2)不同产品,可复用相同的产品创建流程。
3)简化客户端调用方式。去除多参构造的方式。
4)分步骤创建对象。
缺点:
增加多个类,代码复杂度增加。