java - 具有泛型的构建器

Question

我有以下层次结构

名为的双泛型类

public class Service<T, U> 
{
    private final Supplier<T>
    private final Function<T, U>
    private final Consumer<U>
    // more fields and methods ...
}

该类的构建器 ServiceBuilder<T, U>使用通常的流畅 API 构建器

public class ServiceBuilder<T, U>
{
    private Supplier<T> supplier;
    private Function<T, U> mapper;
    private Consumer<U> consumer;
    // more fields and methods ....

    public ServiceBuilder<T, U> withSupplier(Supplier<T> supplier)
    {
        this.supplier = supplier;
        return this;
    }

    // more fields and methods ....

    public Service<T, U> build()
    {
        return new Service(supplier, mapper, consumer);
    }
}

基于此，我想提供一个易于使用的T的Supplier，比如说DummySupplier

public class DummySupplier implements Supplier<SomeObject>
{
    public SomeObject get()
    {
        return new SomeObject();
    }
}

我想要一个ServiceBuilder<SomeObject, T>利用该供应商，有效地修复 T这样我只需要一个Function<SomeObject, U> mapper和一个 Consumer<U> consumer>构建我的服务。

我该如何处理这个问题？扩展ServiceBuilder不起作用，因为我想重用的所有现有方法都返回 ServiceBuilder而不是某个类扩展 ServiceBuilder ...

是否有一些已知的模式可供采用？

Answer 1

都不是Function<SomeObject, U> mapper也不SomeObject知道DummySupplier 。此信息必须放置在某个位置，例如 SpecializedServiceBuilder :

public class SpecializedServiceBuilder<U> extends ServiceBuilder<SomeObject, U> {

    ServiceBuilder withSomeObjectFunction(Function<SomeObject, U> mapper) {
        this.supplier = new DummySupplier();
        this.mapper = mapper;
        return this;
    }
}