Question

我一直在尝试破译Java的Alexa智能家居指令API，并且遇到了我从未见过的结构，无法弄清楚如何在搜索中引用它。我知道泛型，但这显然是不同的（至少我认为）。有人可以向我解释使用<Req extends Request <Res>, Res extends Response>的受保护方法声明中发生了什么吗？

public abstract class SmartHomeDirectiveHandler implements 
   RequestStreamHandler {
      private static Gson gson = new Gson();
      private static HandlerFactory factory = new HandlerFactory();

   protected <Req extends Request<Res>, Res extends Response> void 
      registerHandler(MessageName name,RequestHandler<Req, Res> handler) {

      factory.registerHandler(name, handler);
   }

   abstract protected void init();

   protected SmartHomeDirectiveHandler() {
      this.init();
   }

   public final void handleRequest(InputStream inputStream, OutputStream 
      outputStream, Context context) throws IOException {
         JsonReader reader = new JsonReader(new 
         InputStreamReader(inputStream));
         SmartHomeDirectiveRequest request = gson.fromJson(reader, 
         SmartHomeDirectiveRequest.class);
         RequestHandler handler = 
         factory.getHandler(request.getHeader().getName());
         Request req = PayloadDeserializer.deserializePayload(request);
         Response responsePayload;

         try {
            responsePayload = handler.handle(req);
         } catch (Exception e) {
            throw new IOException(e);
           }


         SmartHomeDirectiveResponse response = new 
            SmartHomeDirectiveResponse();

         Header responseHeader = new Header();
         responseHeader.setName(responsePayload.getMessageName());
         responseHeader.setMessageId(request.getHeader().getMessageId());
         responseHeader.setPayloadVersion(request.getHeader()
           .getPayloadVersion());
         responseHeader.setNamespace(request.getHeader().getNamespace());

         response.setHeader(responseHeader);
         response.setPayload(responsePayload);

         OutputStreamWriter writer = new OutputStreamWriter(outputStream);
         writer.write(gson.toJson(response, 
         SmartHomeDirectiveResponse.class));
         writer.flush();
      }
   }

Answer 1

为简化答案，定义了具有通用参数的方法，如下所示：

public <T> void methodName(T parameterName){
    //stuff 
}

在您的情况下，该方法具有两种通用类型，因此（再次简化）为：

public <T,E> void methodName(T parameterName, E parameterTwoName){
    //stuff 
}

最后，这些泛型具有上限，因此结果：

public <T  extends Request<E>  ,E extends Response > void methodName(T parameterName, E parameterTwoName){
    //stuff 
}

了解<req extend =“” request <res =“”>，Res扩展Java方法声明中的Response>

1 个答案: