Builder Pattern
2017/04/10
Definition
The intent of the Builder design pattern is to separate the construction of a complex object from its representation. By doing so the same construction process can create different representations.
Participants
- Product 表示被构造的复杂对象
- Builder 指定
Product各个部件的创建过程的接口(或抽象类) - ConcreteBuilder 实现
Builder - Director 使用Builder的实例实际创建一个
Product
Description
Builder处理Director的请求。Client从Director获取Product。Builder和ConcreteBuilder都不应该有部件的具体业务数据，它们只负责抽象的创建过程。具体的数据只出现在Director。Builder的组件方法的返回类型设定为Builder类本身可以实现 fluent interface
Practice
Ordinary Version
// Product
@Data // using Lombok
class Car {
private int wheels;
private String color;
}
// Builder
interface CarBuilder {
CarBuilder setWheels(final int wheels);
CarBuilder setColor(final String color);
Car build();
}
class CarBuilderImpl implements CarBuilder {
private Car car;
public CarBuilderImpl() {
car = new Car();
}
@Override
public CarBuilder setWheels(final int wheels) {
car.setWheels(wheels);
return this;
}
@Override
public CarBuilder setColor(final String color) {
car.setColor(color);
return this;
}
@Override
public Car build() {
return car;
}
}
// Director
public class CarBuildDirector {
private CarBuilder builder;
public CarBuildDirector(final CarBuilder builder) {
this.builder = builder;
}
public Car construct() {
return builder.setWheels(4)
.setColor("Red")
.build();
}
public static void main(final String[] arguments) {
CarBuilder builder = new CarBuilderImpl();
CarBuildDirector carBuildDirector = new CarBuildDirector(builder);
System.out.println(carBuildDirector.construct());
}
}
Generic Version
我们可以使用Java8实现一个泛型的Builder,很强大！
public class GenericBuilder<T> {
private final Supplier<T> instantiator;
private List<Consumer<T>> instanceModifiers = new ArrayList<>();
public GenericBuilder(Supplier<T> instantiator) {
this.instantiator = instantiator;
}
public static <T> GenericBuilder<T> of(Supplier<T> instantiator) {
return new GenericBuilder<T>(instantiator);
}
public <U> GenericBuilder<T> with(BiConsumer<T, U> consumer, U value) {
Consumer<T> c = instance -> consumer.accept(instance, value);
instanceModifiers.add(c);
return this;
}
public T build() {
T value = instantiator.get();
instanceModifiers.forEach(modifier -> modifier.accept(value));
instanceModifiers.clear();
return value;
}
public static void main(String[] args) {
Car car = GenericBuilder.of(Car::new)
.with(Car::setColors, "red")
.with(Car::setWheels, 5)
.build();
}
}