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Java 生成器模式讲解和代码示例

2023-09-19 82
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简介： Java 生成器模式讲解和代码示例

使用示例：生成器模式是 Java 世界中的一个著名模式。 当你需要创建一个可能有许多配置选项的对象时， 该模式会特别有用。

生成器在 Java 核心程序库中得到了广泛的应用：

  • java.lang.StringBuilder#append()（非同步）
  • java.lang.StringBuffer#append()（同步）
  • java.nio.ByteBuffer#put()（还有 Char­Buffer、Short­Buffer、Int­Buffer、Long­Buffer、Float­Buffer 和 Double­Buffer）
  • javax.swing.GroupLayout.Group#addComponent()
  • java.lang.Appendable的所有实现

识别方法： 生成器模式可以通过类来识别， 它拥有一个构建方法和多个配置结果对象的方法。 生成器方法通常支持方法链 （例如 someBuilder->setValueA(1)->setValueB(2)->create()）。


01分步制造骑车

在本例中， 生成器模式允许你分步骤地制造不同型号的汽车。

示例还展示了生成器如何使用相同的生产过程制造不同类型的产品 （汽车手册）。

主管控制着构造顺序。 它知道制造各种汽车型号需要调用的生产步骤。 它仅与汽车的通用接口进行交互。 这样就能将不同类型的生成器传递给主管了。

最终结果将从生成器对象中获得， 因为主管不知道最终产品的类型。 只有生成器对象知道自己生成的产品是什么。

builders

builders/Builder.java: 通用生成器接口

package refactoring_guru.builder.example.builders;
import refactoring_guru.builder.example.cars.CarType;
import refactoring_guru.builder.example.components.Engine;
import refactoring_guru.builder.example.components.GPSNavigator;
import refactoring_guru.builder.example.components.Transmission;
import refactoring_guru.builder.example.components.TripComputer;
/**
 * Builder interface defines all possible ways to configure a product.
 */
public interface Builder {
    void setCarType(CarType type);
    void setSeats(int seats);
    void setEngine(Engine engine);
    void setTransmission(Transmission transmission);
    void setTripComputer(TripComputer tripComputer);
    void setGPSNavigator(GPSNavigator gpsNavigator);
}

builders/CarBuilder.java: 汽车生成器

package refactoring_guru.builder.example.builders;
import refactoring_guru.builder.example.cars.Car;
import refactoring_guru.builder.example.cars.CarType;
import refactoring_guru.builder.example.components.Engine;
import refactoring_guru.builder.example.components.GPSNavigator;
import refactoring_guru.builder.example.components.Transmission;
import refactoring_guru.builder.example.components.TripComputer;
/**
* Concrete builders implement steps defined in the common interface.
*/
public class CarBuilder implements Builder {
    private CarType type;
    private int seats;
    private Engine engine;
    private Transmission transmission;
    private TripComputer tripComputer;
    private GPSNavigator gpsNavigator;
    public void setCarType(CarType type) {
        this.type = type;
    }
    @Override
    public void setSeats(int seats) {
        this.seats = seats;
    }
    @Override
    public void setEngine(Engine engine) {
        this.engine = engine;
    }
    @Override
    public void setTransmission(Transmission transmission) {
        this.transmission = transmission;
    }
    @Override
    public void setTripComputer(TripComputer tripComputer) {
        this.tripComputer = tripComputer;
    }
    @Override
    public void setGPSNavigator(GPSNavigator gpsNavigator) {
        this.gpsNavigator = gpsNavigator;
    }
    public Car getResult() {
        return new Car(type, seats, engine, transmission, tripComputer, gpsNavigator);
    }
}

builders/CarManualBuilder.java: 汽车手册生成器

package refactoring_guru.builder.example.builders;
import refactoring_guru.builder.example.cars.Manual;
import refactoring_guru.builder.example.cars.CarType;
import refactoring_guru.builder.example.components.Engine;
import refactoring_guru.builder.example.components.GPSNavigator;
import refactoring_guru.builder.example.components.Transmission;
import refactoring_guru.builder.example.components.TripComputer;
/**
* Unlike other creational patterns, Builder can construct unrelated products,
* which don't have the common interface.
*
* In this case we build a user manual for a car, using the same steps as we
* built a car. This allows to produce manuals for specific car models,
* configured with different features.
*/
public class CarManualBuilder implements Builder{
    private CarType type;
    private int seats;
    private Engine engine;
    private Transmission transmission;
    private TripComputer tripComputer;
    private GPSNavigator gpsNavigator;
    @Override
    public void setCarType(CarType type) {
        this.type = type;
    }
    @Override
    public void setSeats(int seats) {
        this.seats = seats;
    }
    @Override
    public void setEngine(Engine engine) {
        this.engine = engine;
    }
    @Override
    public void setTransmission(Transmission transmission) {
        this.transmission = transmission;
    }
    @Override
    public void setTripComputer(TripComputer tripComputer) {
        this.tripComputer = tripComputer;
    }
    @Override
    public void setGPSNavigator(GPSNavigator gpsNavigator) {
        this.gpsNavigator = gpsNavigator;
    }
    public Manual getResult() {
        return new Manual(type, seats, engine, transmission, tripComputer, gpsNavigator);
    }
}

 cars

cars/Car.java: 汽车产品

package refactoring_guru.builder.example.cars;
import refactoring_guru.builder.example.components.Engine;
import refactoring_guru.builder.example.components.GPSNavigator;
import refactoring_guru.builder.example.components.Transmission;
import refactoring_guru.builder.example.components.TripComputer;
/**
* Car is a product class.
*/
public class Car {
    private final CarType carType;
    private final int seats;
    private final Engine engine;
    private final Transmission transmission;
    private final TripComputer tripComputer;
    private final GPSNavigator gpsNavigator;
    private double fuel = 0;
    public Car(CarType carType, int seats, Engine engine, Transmission transmission,
               TripComputer tripComputer, GPSNavigator gpsNavigator) {
        this.carType = carType;
        this.seats = seats;
        this.engine = engine;
        this.transmission = transmission;
        this.tripComputer = tripComputer;
        if (this.tripComputer != null) {
            this.tripComputer.setCar(this);
        }
        this.gpsNavigator = gpsNavigator;
    }
    public CarType getCarType() {
        return carType;
    }
    public double getFuel() {
        return fuel;
    }
    public void setFuel(double fuel) {
        this.fuel = fuel;
    }
    public int getSeats() {
        return seats;
    }
    public Engine getEngine() {
        return engine;
    }
    public Transmission getTransmission() {
        return transmission;
    }
    public TripComputer getTripComputer() {
        return tripComputer;
    }
    public GPSNavigator getGpsNavigator() {
        return gpsNavigator;
    }
}

cars/Manual.java: 手册产品

package refactoring_guru.builder.example.cars;
import refactoring_guru.builder.example.components.Engine;
import refactoring_guru.builder.example.components.GPSNavigator;
import refactoring_guru.builder.example.components.Transmission;
import refactoring_guru.builder.example.components.TripComputer;
/**
* Car manual is another product. Note that it does not have the same ancestor
* as a Car. They are not related.
*/
public class Manual {
    private final CarType carType;
    private final int seats;
    private final Engine engine;
    private final Transmission transmission;
    private final TripComputer tripComputer;
    private final GPSNavigator gpsNavigator;
    public Manual(CarType carType, int seats, Engine engine, Transmission transmission,
                  TripComputer tripComputer, GPSNavigator gpsNavigator) {
        this.carType = carType;
        this.seats = seats;
        this.engine = engine;
        this.transmission = transmission;
        this.tripComputer = tripComputer;
        this.gpsNavigator = gpsNavigator;
    }
    public String print() {
        String info = "";
        info += "Type of car: " + carType + "\n";
        info += "Count of seats: " + seats + "\n";
        info += "Engine: volume - " + engine.getVolume() + "; mileage - " + engine.getMileage() + "\n";
        info += "Transmission: " + transmission + "\n";
        if (this.tripComputer != null) {
            info += "Trip Computer: Functional" + "\n";
        } else {
            info += "Trip Computer: N/A" + "\n";
        }
        if (this.gpsNavigator != null) {
            info += "GPS Navigator: Functional" + "\n";
        } else {
            info += "GPS Navigator: N/A" + "\n";
        }
        return info;
    }
}
 cars/CarType.java
package refactoring_guru.builder.example.cars;
public enum CarType {
    CITY_CAR, SPORTS_CAR, SUV
}

components

components/Engine.java: 产品特征 1

package refactoring_guru.builder.example.components;
/**
* Just another feature of a car.
*/
public class Engine {
    private final double volume;
    private double mileage;
    private boolean started;
    public Engine(double volume, double mileage) {
        this.volume = volume;
        this.mileage = mileage;
    }
    public void on() {
        started = true;
    }
    public void off() {
        started = false;
    }
    public boolean isStarted() {
        return started;
    }
    public void go(double mileage) {
        if (started) {
            this.mileage += mileage;
        } else {
            System.err.println("Cannot go(), you must start engine first!");
        }
    }
    public double getVolume() {
        return volume;
    }
    public double getMileage() {
        return mileage;
    }
}

components/GPSNavigator.java: 产品特征 2

package refactoring_guru.builder.example.components;
/**
* Just another feature of a car.
*/
public class GPSNavigator {
    private String route;
    public GPSNavigator() {
        this.route = "221b, Baker Street, London  to Scotland Yard, 8-10 Broadway, London";
    }
    public GPSNavigator(String manualRoute) {
        this.route = manualRoute;
    }
    public String getRoute() {
        return route;
    }
}

components/Transmission.java: 产品特征 3

package refactoring_guru.builder.example.components;
/**
* Just another feature of a car.
*/
public enum Transmission {
    SINGLE_SPEED, MANUAL, AUTOMATIC, SEMI_AUTOMATIC
}

components/TripComputer.java: 产品特征 4

package refactoring_guru.builder.example.components;
import refactoring_guru.builder.example.cars.Car;
/**
* Just another feature of a car.
*/
public class TripComputer {
    private Car car;
    public void setCar(Car car) {
        this.car = car;
    }
    public void showFuelLevel() {
        System.out.println("Fuel level: " + car.getFuel());
    }
    public void showStatus() {
        if (this.car.getEngine().isStarted()) {
            System.out.println("Car is started");
        } else {
            System.out.println("Car isn't started");
        }
    }
}

director

director/Director.java: 主管控制生成器

package refactoring_guru.builder.example.director;
import refactoring_guru.builder.example.builders.Builder;
import refactoring_guru.builder.example.cars.CarType;
import refactoring_guru.builder.example.components.Engine;
import refactoring_guru.builder.example.components.GPSNavigator;
import refactoring_guru.builder.example.components.Transmission;
import refactoring_guru.builder.example.components.TripComputer;
/**
* Director defines the order of building steps. It works with a builder object
* through common Builder interface. Therefore it may not know what product is
* being built.
*/
public class Director {
    public void constructSportsCar(Builder builder) {
        builder.setCarType(CarType.SPORTS_CAR);
        builder.setSeats(2);
        builder.setEngine(new Engine(3.0, 0));
        builder.setTransmission(Transmission.SEMI_AUTOMATIC);
        builder.setTripComputer(new TripComputer());
        builder.setGPSNavigator(new GPSNavigator());
    }
    public void constructCityCar(Builder builder) {
        builder.setCarType(CarType.CITY_CAR);
        builder.setSeats(2);
        builder.setEngine(new Engine(1.2, 0));
        builder.setTransmission(Transmission.AUTOMATIC);
        builder.setTripComputer(new TripComputer());
        builder.setGPSNavigator(new GPSNavigator());
    }
    public void constructSUV(Builder builder) {
        builder.setCarType(CarType.SUV);
        builder.setSeats(4);
        builder.setEngine(new Engine(2.5, 0));
        builder.setTransmission(Transmission.MANUAL);
        builder.setGPSNavigator(new GPSNavigator());
    }
}

Demo.java: 客户端代码

package refactoring_guru.builder.example;
import refactoring_guru.builder.example.builders.CarBuilder;
import refactoring_guru.builder.example.builders.CarManualBuilder;
import refactoring_guru.builder.example.cars.Car;
import refactoring_guru.builder.example.cars.Manual;
import refactoring_guru.builder.example.director.Director;
/**
* Demo class. Everything comes together here.
*/
public class Demo {
    public static void main(String[] args) {
        Director director = new Director();
        // Director gets the concrete builder object from the client
        // (application code). That's because application knows better which
        // builder to use to get a specific product.
        CarBuilder builder = new CarBuilder();
        director.constructSportsCar(builder);
        // The final product is often retrieved from a builder object, since
        // Director is not aware and not dependent on concrete builders and
        // products.
        Car car = builder.getResult();
        System.out.println("Car built:\n" + car.getCarType());
        CarManualBuilder manualBuilder = new CarManualBuilder();
        // Director may know several building recipes.
        director.constructSportsCar(manualBuilder);
        Manual carManual = manualBuilder.getResult();
        System.out.println("\nCar manual built:\n" + carManual.print());
    }
}

OutputDemo.txt: 执行结果

Car built:
SPORTS_CAR
Car manual built:
Type of car: SPORTS_CAR
Count of seats: 2
Engine: volume - 3.0; mileage - 0.0
Transmission: SEMI_AUTOMATIC
Trip Computer: Functional
GPS Navigator: Functional
文章标签：
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关键词：
Java代码
Java示例
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