边读边写，流式中继

流式中继

publicvoidrelay(@PathVariableStringfileId,ServletResponseservletResponse)throwsException{// 1. 从 A 获取流URLurl=newURL("http://A/download/"+fileId);URLConnectionconn=url.openConnection();InputStreamaIn=conn.getInputStream();// 2. 打开 B 的输出流（HTTP chunked）URLbUrl=newURL("http://B/upload");HttpURLConnectionbConn=(HttpURLConnection)bUrl.openConnection();bConn.setDoOutput(true);bConn.setFixedLengthStreamingMode(conn.getContentLength());bConn.setRequestProperty("Content-Type","application/octet-stream");OutputStreambOut=bConn.getOutputStream();// 3. 边读边写（核心）byte[]buffer=newbyte[8*1024];longtotal=0;intlen;while((len=aIn.read(buffer))!=-1){bOut.write(buffer,0,len);total+=len;}bOut.flush();bOut.close();aIn.close();// 4. 可选：检查 B 响应if(bConn.getResponseCode()!=200){thrownewRuntimeException("B upload failed");}}