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Thread: How to use PrintSteam and BufferedReader Simultaneously

  1. #1
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    Default How to use PrintSteam and BufferedReader Simultaneously


    I am working with an electronic device that receives commands and sends ASCII data to the client using the socket functionality in Java. I have no problems using PrintStream sending commands or using BufferedReader to receive data from the electronic device separately. The problem I am currently having is receiving data from the electronic device immeditately after I send it a command string. For example there is a command string that I can send to the device and by doing so the device will return the settings in ASCII data.

    Here is my code:

                //Create a connection to server
                Socket s = new Socket(ipAddress, portNumber);
                //Create input and output streams to socket
                PrintStream out = new PrintStream(s.getOutputStream());
                //Create input streams to socket
                BufferedReader in = new BufferedReader(new InputStreamReader(s.getInputStream()));
                //send the command string to the barcode reader 
                out.print("sRN LocationName");  
                //receive data from barcode reader that the command string initiated
                String line = in.readLine();
                System.out.println("Text received: " + line);
                //close the stream
                //close the stream
                //close the socket
            }catch (SocketException e )
                //for debugging purposes
                System.err.println ("Socket error : " + e);
            }catch (UnknownHostException e )
                //for debugging purposes
                System.err.println ("Invalid host!");
            }catch (IOException e )
                //for debugging purposes
                System.err.println ("I/O error : " + e);

    Everytime I try it I get no return data through BufferedReader. I know it works because I have tested in Hyperterminal and it works everytime.

    Any help is appreciated.

    Thanks in advanced

  2. #2
    Super Moderator helloworld922's Avatar
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    Default Re: How to use PrintSteam and BufferedReader Simultaneously

    I'm not completely positive if this will fix your problem, but I know that sometimes you have to manually flush the stream. You could give that a go and see if it works.

    You can check to see if your program is actually sending something out the socket by using a profiling program (I recommend WireShark, it's a very nice open-source network monitor). Conversely, you can also check to see if you're receiving anything back.

  3. #3
    Think of me.... Mr.777's Avatar
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    Default Re: How to use PrintSteam and BufferedReader Simultaneously

    Each time you send the message from your device is submitted successfully, but you try to read it as fast as it's not still flushed. Use flush() to clear your output memory buffer and force it to write over the destination.
    Remember, flush() will throw IO exception, handle it and i don't think if outputstream or bufferedstream will allow flush() as documentation says, they both don't work.
    Anyways, give it a try, may be it will work.

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