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，用一个流畅的界面模拟命名参数。

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

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

service和output是必填参数，sensor是必填参数。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location，用于指定服务类型（分别为直接或反向地理编码）。我用新的儿童班来代表这种相互排斥。

我想象类层次结构：

  .-----.
  | 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https://stackoverflow.com/a/9138629/946814上建立我的答案，但考虑到这个多级层次结构。

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()方法来返回层次结构的叶对象。为了向层次结构传递其类型，父类具有通用T，并且叶子将T绑定到自身。

它确保了类型安全性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...
}

生成器模式与继承

1 个答案: