java - 将 OutputStream 与 InputStream 连接起来

Question

我正在试验一个小型网络框架，偶然发现了一个与流有关的问题。有像 Response get(HttpServletRequest) 这样的处理程序方法。从框架的角度来看，响应应该为响应主体提供输入流。框架读取此流并将数据写入 Servlet API 的底层 OutputStream。但是从用户的角度来看，需要写入一个 OutputStream。

框架的观点:

public interface Response {
  InputStream getInputStream();
}

用户视角:

public interface Response {
  InputStream getOutputStream();
}

应该这样使用:

public void get(HttpServletRequest request) {
  Response response = new Response(OK);
  response.getOutputStream().write(...);
  return response;
}

问题是我无法在没有输出目标的情况下创建输出流(并且不想写入 ByteArray 缓冲区)。

知道如何给用户一个 OutputStream 而不像在 Servlet API 中那样传入吗？我想避免输出参数。

Answer 1

同时抽象/装饰Request，并从中获取Response。

例如在您的前端 Controller servlet 中:

protected void doGet(HttpServletRequest req, HttpServletResponse res) throws ServletException, IOException {
    Request request = new RequestImpl(req, res);
    Action action = ActionFactory.getAction(req); // Do whatever way you do to locate the `Action`.
    Response = action.get(request);
    // ...
}

其中 RequestImpl 看起来像这样:

public class RequestImpl implements Request {
    private HttpServletRequest request;
    private HttpServletResponse response;

    public RequestImpl(HttpServletRequest request, HttpServletResponse response) {
        this.request = request;
        this.response = response;
    }

    public Response newResponse(Status status) {
        return new ResponseImpl(response, status);
        // Add a boolean responseCreated to avoid creation of multiple responses? Illegal state!
    }

    public String getParameter(String name) { // Just another example of decorated method.
        return request.getParameter(name);
    }

    // ...
}

ResponseImpl 看起来像这样:

public class ResponseImpl implements Response {
    private HttpServletResponse response;

    public ResponseImpl(HttpServletResponse response, Status status) {
        this.response = response;
        this.response.setStatus(status.getCode());
    }

    public OutputStream getOutputStream() {
        return response.getOutputStream();
    }

    // ...
}

你最终在你的 Action 中使用它:

public ActionImpl implements Action {
    public Response get(Request request) {
        Response response = request.newResponse(OK);
        response.getOutputStream().write("body");
        return response;
    }
}

---

或者，您也可以创建一个 Context，它同时接收 HttpServletRequest 和 HttpServletResponse 并将其传递给 Request。这也或多或少是普通 MVC 框架所做的。例如

protected void service(HttpServletRequest req, HttpServletResponse res) throws ServletException, IOException {
    Context context = new ContextImpl(req, res);
    Action action = ActionFactory.getAction(req); // Do whatever way you do to locate the `Action`.
    action.execute(context);
    context.render(); // Do here whatever you'd initially to do with the obtained Response.
}

与

public ActionImpl implements Action {
    public void execute(Context context) {
        context.getResponseOutputStream().write("body");
    }
}

---

也就是说，与其重新发明，我建议也看看现有的 API。根据您想做什么，JSF、JAX-RS 或 JAX-WS 可能正是您真正想要的。除非这是出于纯粹的爱好目的；)