Builder em Java

O Builder é um padrão de projeto criacional, que permite a construção de objetos complexos passo a passo.

Diferente de outros padrões de criação, o Builder não exige que os produtos tenham uma interface comum. Isso torna possível produzir produtos diferentes usando o mesmo processo de construção.

Saiba mais sobre o Builder

Complexidade:

Popularidade:

Exemplos de uso: O padrão Builder é um padrão bem conhecido no mundo Java. É especialmente útil quando você precisa criar um objeto com muitas opções possíveis de configuração.

O Builder é amplamente usado nas bibliotecas principais do Java:

java.lang.StringBuilder#append() (unsynchronized)
java.lang.StringBuffer#append() (synchronized)
java.nio.ByteBuffer#put() (também em CharBuffer, ShortBuffer, IntBuffer, LongBuffer, FloatBuffer e DoubleBuffer)
javax.swing.GroupLayout.Group#addComponent()
Todas as implementações de java.lang.Appendable

Identificação: O padrão Builder pode ser reconhecido na classe que possui um único método de criação e vários métodos para configurar o objeto resultante. Os métodos do Builder geralmente suportam encadeamento (por exemplo, algumBuilder->configValorA(1)->configValorB(2)->criar()).

Produção de um automóvel passo a passo

Neste exemplo, o padrão Builder permite a construção passo a passo de diferentes modelos de carros.

O exemplo também mostra como o Builder produz produtos de diferentes tipos (manual do carro) usando as mesmas etapas de construção.

O diretor controla a ordem da construção. Ele sabe quais etapas de construção chamar para produzir este ou aquele modelo de carro. Ele funciona com builders apenas por meio de sua interface comum. Isso permite passar diferentes tipos de builders para o diretor.

O resultado final é recuperado do objeto builder porque o diretor não pode saber o tipo de produto resultante. Somente o objeto builder sabe o que exatamente ele cria.

builders

builders/Builder.java: Interface do builder comum

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: Builder do carro

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: Builder do manual do carro

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: Produto do carro

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: Produto do manual

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: Funcionalidade 1 do produto

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: Funcionalidade 2 do produto

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: Funcionalidade 3 do produto

package refactoring_guru.builder.example.components;

/**
 * Just another feature of a car.
 */
public enum Transmission {
    SINGLE_SPEED, MANUAL, AUTOMATIC, SEMI_AUTOMATIC
}

components/TripComputer.java: Funcionalidade 4 do produto

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: Diretor controla os builders

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: Código cliente

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: Resultados da execução

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