生成器模式与继承

Question

我想将Web服务URL请求表示为对象,并发现有许多常见参数可以在继承层次结构中"冒泡".一个请求可能有很多参数,一些是必需的,另一些是可选的,我相信Bloch的Builder模式是一个很好的选择,用一个流畅的接口模拟命名参数.

具体来说,我正在设计Google Maps Web服务API,它具有一般的Web服务请求

http://maps.googleapis.com/maps/api/service/output?{parameters}

service并且output是必需参数和sensor必需参数.还有一个可选参数language.

每个服务都有一组强制和可选参数.地理编码服务有两个可选参数,bounds和region.它还具有互斥的强制参数,address或者location指定服务类型(分别为直接或反向地理编码).我用新的儿童班来代表这种互斥.

我想象类层次结构如下:

  .-----.
  | Url |
  '-----'
     ^
     |
.---------.
| Request |
'---------'
     ^
     |----------------------------+--------------...
.---------.                 .------------.
| Geocode |                 | Directions |
'---------'                 '------------'
     ^                            ^
     |------------+               .
 .--------.  .---------.          .
 | Direct |  | Reverse |          .
 '--------'  '---------'

然后,我想做类似以下的事情:

String output = "xml";
boolean sensor = true;
String address = "Av. Paulista, São Paulo, Brasil";
Bounds bounds  = new Bounds(-20, -10, -25, -20); //Geographic rectangle
String region  = "br";
String lang    = "pt-BR";
Coord location = new Coord(-12,-22);

DirectGeocodeRequestUrl direct = 
    new DirectGeocodeRequestUrl.Builder(output, sensor, address)
                               .bounds(bounds)
                               .language(lang)
                               .build();

ReverseGeocodeRequestUrl reverse = 
    new ReverseGeocodeRequestUrl.Builder(output, sensor, location)
                                .language(lang)
                                .region(region)
                                .build();

如何创建一个使用类和插入它的超类中的参数和方法的构建器？

Answer 1

我正在/sf/answers/639704061/上建立我的答案,但考虑到这个多层次的层次结构.

我们需要的是使用Builder内部类复制相同的层次结构.由于我们需要方法链接,我们需要一个getThis()返回层次结构的叶对象的方法.为了将其类型向上传递给层次结构,父类具有泛型T,并且叶子绑定T到自身.

它确保了类型安全,并避免因未初始化的强制参数或拼写错误而导致的任何异常抛出,以及良好的流畅界面.然而,代表如URL这样简单的结构是一种非常昂贵和复杂的设计.我希望它对某些人有用 - 我最后喜欢字符串连接.

RequestUrl:

public abstract class RequestUrl{
    public static abstract class Builder<T extends Builder<T>>{
        protected String output;
        protected boolean sensor;
        //Optional parameters can have default values
        protected String lang = "en"; 

        public Builder(String output, boolean sensor){
            this.output = output;
            this.sensor = sensor;
        }

        public T lang(String lang){
            this.lang = lang;
            return getThis();
        }

        public abstract T getThis();
    }

    final private String output;
    final private boolean sensor;
    final private String lang;

    protected RequestUrl(Builder builder){
        this.output = builder.output;
        this.sensor = builder.sensor;
        this.lang = builder.lang;
    }

    // other logic...
}

GeocodeRequestUrl:

public abstract class GeocodeRequestUrl extends RequestUrl {
    public static abstract class Builder<T extends Builder<T>>
        extends RequestUrl.Builder<Builder<T>>{

        protected Bounds bounds;
        protected String region = "us";

        public Builder(String output, boolean sensor){
            super( output, sensor );
        }

        public T bounds(Bounds bounds){
            this.bounds = bounds;
            return getThis();
        }

        public T region(String region){
            this.region = region;
            return getThis();
        }

        @Override
        public abstract T getThis();
    }

    final private Bounds bounds;
    final private String region;

    protected GeocodeRequestUrl(Builder builder){
        super (builder);
        this.bounds = builder.bounds;
        this.region = builder.region;
    }

    // other logic...
}

DirectGeocodeRequestUrl:

public class DirectGeocodeRequestUrl extends GeocodeRequestUrl {
    public static class Builder<Builder>
        extends GeocodeRequestUrl.Builder<Builder>{

        protected String address;

        public Builder(String output, boolean sensor, String address){
            super( output, sensor );
            this.address = address;
        }

        @Override
        public Builder getThis(){
            return this;
        }

        public DirectGeocodeRequestUrl build(){
            return new DirectGeocodeRequestUrl(this);
        }
    }

    final private String address;

    protected DirectGeocodeRequestUrl(Builder builder){
        super (builder);
        this.address = builder.address;
    }

    // other logic...
}

ReverseGeocodeRequestUrl:

public class ReverseGeocodeRequestUrl extends GeocodeRequestUrl {
    public static class Builder<Builder>
        extends GeocodeRequestUrl.Builder<Builder>{

        protected Coord location;

        public Builder(String output, boolean sensor, Coord location){
            super( output, sensor );
            this.location = location;
        }

        @Override
        public Builder getThis(){
            return this;
        }

        public ReverseGeocodeRequestUrl build(){
            return new ReverseGeocodeRequestUrl(this);
        }
    }

    final private Coord location;

    protected ReverseGeocodeRequestUrl(Builder builder){
        super (builder);
        this.location = builder.location;
    }

    // other logic...
}