自己用 java socket 写了一个文件上传下载的小工具，分为服务端和客户端，客户端上传文件，服务端接收文件。但是部署之后，服务端的输入流总是被阻塞，有大佬能看出是什么问题吗？

客户端代码：

public static String upload(String fileName, FileInputStream fis) {     if (fis == null) {         System.out.println("FileInputStream Is Null");         return null;     }     Socket storageSocket = null;     DataOutputStream dos = null;     DataInputStream dis = null;     String filePath = null;     try {         System.out.println("00000000000");         RapidMessage contactMsg = Contactor.contact(BaseProtocol.UPLOAD_COMMAND);         if (contactMsg.getStatus() != 200) {             System.out.println(contactMsg.getResult());             return null;         }         System.out.println(contactMsg.getResult());         storageSocket = new Socket(InetAddress.getByName(contactMsg.getResult()), Integer.parseInt(ConfigLoader.STORAGE_PORT));         dos = new DataOutputStream(storageSocket.getOutputStream());         dos.write(Contactor.getHeader(BaseProtocol.UPLOAD_COMMAND));         dos.writeUTF(fileName);         byte[] fileBytes = new byte[1024];         System.out.println("11111111111");         int length;         while ((length = fis.read(fileBytes)) != -1) {             System.out.println("------");             dos.write(fileBytes, 0, length);         }         System.out.println("22222222222");         storageSocket.shutdownOutput();         dis = new DataInputStream(storageSocket.getInputStream());         System.out.println("33333333333");         int status = dis.read();         System.out.println("44444444444");         String result = dis.readUTF();         System.out.println("55555555555");         if (status != 200) {             System.out.println(result);             return null;         }         System.out.println("66666666666");         filePath = result;         System.out.println("Upload Success: " + filePath);     } catch (IOException e) {         e.printStackTrace();     } finally {         try {             fis.close();             if (dis != null) {                 dis.close();             }             if (dos != null) {                 dos.close();             }             if (storageSocket != null) {                 storageSocket.close();             }         } catch (IOException e) {             e.printStackTrace();         }     }     return filePath; } 

服务端代码：

public static void upload(Socket connection) {      System.out.println("eeeeeeeeeeeeeeeeeeeeeeeeeeeee");      DataInputStream dis = null;     FileOutputStream fos = null;     try {          System.out.println("ffffffffffffffffffffffffffff");          dis = new DataInputStream(connection.getInputStream());          System.out.println("ggggggggggggggggggggggggggggg");          String stage_path = Initializer.STORE_PATH + "/" + Initializer.currentStage;         File stagePath = new File(stage_path);          System.out.println("hhhhhhhhhhhhhhhhhhhhhhhhhhhhh");          if (!stagePath.exists()) {             Logger.error("Path Not Found: " + stage_path);             Sweeper.close(connection, BaseProtocol.RESPONSE_FAILURE, "Path Not Found: " + stage_path);             return;         }         if (!stagePath.isDirectory()) {             Logger.error("Path Is Not A Directory: " + stage_path);             Sweeper.close(connection, BaseProtocol.RESPONSE_FAILURE, "Path Is Not A Directory: " + stage_path);             return;         }          System.out.println("iiiiiiiiiiiiiiiiiiiiiiiiiiiii");          String storageId = Integer.toHexString(Integer.parseInt(Initializer.STORAGE_ID));          System.out.println("jjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjj");          if (storageId.length() == 1) storageId = "0" + storageId;         String encoding = "N" + storageId + new Date().getTime() + (int) (Math.random() * 90 + 10);         byte[] enSrc = encoding.getBytes(StandardCharsets.UTF_8);         String encoded = Base64.getEncoder().encodeToString(enSrc);          System.out.println("kkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkk");          String realName = dis.readUTF();          System.out.println("lllllllllllllllllllllllllllllllllll");          String fileName;         if (realName.contains(".")) {             String extension = realName.substring(realName.lastIndexOf("."));             fileName = encoded + extension;         } else {             fileName = encoded;         }          System.out.println("mmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmm");          File file = new File(stage_path + "/" + fileName);         fos = new FileOutputStream(file);         byte[] bytes = new byte[1024];         int length;          System.out.println("nnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnn");          while ((length = dis.read(bytes)) != -1) {             fos.write(bytes, 0, length);         }          System.out.println("oooooooooooooooooooooooooooooooo");          String uploadPath = "group" + Initializer.GROUP_ID + "/M00/" + Initializer.currentStage + "/" + fileName;         Logger.info("Upload File Success: " + uploadPath);          System.out.println("ppppppppppppppppppppppppppppppppp");          Sweeper.close(connection, BaseProtocol.RESPONSE_SUCCESS, uploadPath);         String[] filesNum = stagePath.list();         if (filesNum != null && filesNum.length > 99) {             Initializer.stageIndex++;             Initializer.currentStage =         Initializer.STAGE_NAMES[Initializer.stageIndex];             Initializer.nextStage = Initializer.STAGE_NAMES[Initializer.stageIndex + 1];         }         System.out.println("uuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuu");     } catch (IOException e) {         e.printStackTrace();     } finally {         try {             if (fos != null) {                 fos.close();             }             if (dis != null) {                 dis.close();             }             if (connection != null) {                 connection.close();             }         } catch (IOException e) {             e.printStackTrace();         }     } } 

服务端代码在输出“kkkkkkkkkkkkkkkkkkkkkkk”之后就不再输出了，又试过几次之后发现，服务端代码有几次也会在输出“nnnnnnnnnnnnnnnnnnnn”之后不再输出。这是什么原因呢？难道 DataInputStream.readUTF()也会阻塞吗？还有难道即使客户端在调用 socket.shutdownoutput()之后，输入端 DataInputStream.read(byte[])仍然会阻塞吗？