从串行通信端口（COM1）读取数据时无法退出循环

Question

I am using https://github.com/rm5248/JavaSerial and developed a project for writing and reading data from serial port. Both are happening perfectly fine, but I am not able to find the last byte of information and come out of the loop.

Any pointers here are highly appreciated.

            portName = currPortId.getName();
        // This would be COM1, COM2, etc on Windows
        // SerialPort s = new SerialPort(portName);
        SerialPort s = new SerialPort("COM1");//, SerialPort.NO_CONTROL_LINE_CHANGE);
        InputStream is = s.getInputStream();
        OutputStream os = s.getOutputStream();

        String st = "";
        st = "5230" + 31 + String.format("%02X", new Object[] { Integer.valueOf(179) })
                + String.format("%02X", new Object[] { Integer.valueOf(83) });
        os.write(hexStringToByteArray(st + "0D"));

        System.out.println("Data written");

        byte[] dataRead = new byte[753];
        int bytesRead = 0;/* = is.read(dataRead); */
        while (bytesRead != -1 /*|| dataRead.equals("end")*//*equals("353535")*/) {
            /*
             * System.out.println("Data in string format is " + new
             * String(dataRead, "UTF-8").replace("\n", "").replace("\r",
             * "").trim());
             */
            // bytesRead = is.read(dataRead);

            bytesRead = is.read(dataRead);

            Thread.sleep(90L);

            System.out.println("bytesRead value is " + bytesRead);

            String theString = new String(dataRead, "UTF-8").replace("\n", "").replace("\r", "").trim();

            System.out.println("theString value is " + theString);

            /*
             * sb[0].append(theString); data.add(sb[0].toString()); if
             * (dataRead[(dataRead.length - 1)] == 13) {
             * data.add(sb[0].toString()); sb[0] = new StringBuilder(); }
             */
            data.add(theString);

            System.out.println("data value is " + data);
        }

I tried some of the things like

  while (bytesRead != -1)
  while(dataRead.equals("end"))
  while(dataRead.equals("353535"))

But was not useful

Answer 1

The InputStream that you get back from the SerialPort follows the same rules that a normal InputStream does, which means that is.read() is a blocking call. The only time that is.read() will return -1 for the end of input is when the serial port is closed.

If you want to read exactly 753 bytes, you should break out of your loop after you have read that number of bytes.