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我正在尝试使用 JAVA NIO 将文件从主机 A 传输到客户端 B，而无需在本地下载文件，然后为客户端 B 提供下载文件的链接。

我正在运行 spark Apache 框架并使用 maven 项目。

我使用以下方法在 Spark 中映射了请求http://localhost:8080/download/hello：get("/download/:id",RequestHandler::downloadHandler);

函数内部是从以下位置下载文件的代码：“ https://download.springsource.com/release/STS/3.8.1.RELEASE/dist/e4.6/spring-tool-suite-3.8.1.发布-e4.6-linux-gtk-x86_64.tar.gz "

try {
            URL url = new URL("https://download.springsource.com/release/STS/3.8.1.RELEASE/dist/e4.6/spring-tool-suite-3.8.1.RELEASE-e4.6-linux-gtk-x86_64.tar.gz");
            HttpURLConnection httpURLConnection = (HttpURLConnection) url.openConnection();
            int respCode = +httpURLConnection.getResponseCode();
            System.out.println("response code : "+respCode);
            if (respCode == HttpURLConnection.HTTP_OK){
                String fileName = "";
                String disposition = httpURLConnection.getHeaderField("Content-Disposition");
                String contentType = httpURLConnection.getContentType();
                int contentLength = httpURLConnection.getContentLength();

                if (disposition != null) {
                    // extracts file name from header field
                    int index = disposition.indexOf("filename=");
                    if (index > 0) {
                        fileName = disposition.substring(index + 10,
                                disposition.length() - 1);
                    }
                } else {
                    // extracts file name from URL
                    fileName = url.toString().substring(url.toString().lastIndexOf("/") + 1,
                            url.toString().length());
                }
                System.out.println("Content-Type = " + contentType);
                System.out.println("Content-Disposition = " + disposition);
                System.out.println("Content-Length = " + contentLength);
                System.out.println("fileName = " + fileName);
                httpURLConnection.disconnect();
                System.out.println("other stuff : ");
                System.out.println(url.getHost());
                ReadableByteChannel readableByteChannel = Channels.newChannel(url.openStream());
                FileOutputStream fileOutputStream = new FileOutputStream(fileName);
                FileChannel fileChannel = fileOutputStream.getChannel();
                fileChannel.transferFrom(readableByteChannel, 0, Long.MAX_VALUE);
                fileOutputStream.close();
                readableByteChannel.close();
            }

        } catch (IOException e) {
            e.printStackTrace();
        }

我使用 httpURLConnection 获取文件名和文件大小，然后进行处理以下载文件。我想要做的是，而不是使用fileChannel.transferFrom(readableByteChannel, 0, Long.MAX_VALUE)将文件直接传输到客户端来在本地下载文件。

我做了一些研究，我认为使用 Socketchannels 是可能的，但我不明白它应该如何工作。

我还阅读了这篇文章 https://examples.javacodegeeks.com/core-java/nio/java-nio-large-file-transfer-tutorial/ 并试图了解 Reciever 类，但我仍然不清楚如何.

我会很感激一些指导。谢谢

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