java – inputstream. Available() is always 0

I don't know what happened to my code I made no mistakes and did not respond I'm writing data to serialport and activating port Notifyondataavailable (true) waits for a response; However, this event is not triggered, InputStream Available() always returns 0 What might be the problem? I use rxtx in Linux

edit

package testConn;  
import forms_helper.global_variables;  
import java.io.BufferedReader; 
import java.io.IOException;  
import java.io.InputStream;  
import java.io.InputStreamReader;  
import java.io.OutputStream;  
import java.io.PrintStream;  
import java.io.UnsupportedEncodingException;  
import java.util.logging.Level;  
import java.util.logging.Logger;  
import javax.comm.*;  
import java.util.*;  
/** Check each port to see if it is open. **/   
public class openPort implements SerialPortEventListener {

    static Enumeration portList;
    static CommPortIdentifier portId;
    static String messageString;
    public static SerialPort serialPort;
    static OutputStream outputStream;
    InputStream inputStream;
    static boolean outputBufferEmptyFlag = false;
    private BufferedReader is;
    private PrintStream os;

    public void open() {
        Enumeration port_list = CommPortIdentifier.getPortIdentifiers();

        while (port_list.hasMoreElements()) {
            // Get the list of ports
            CommPortIdentifier port_id = (CommPortIdentifier) port_list.nextElement();
            if (port_id.getName().equals("/dev/ttyS1")) {

                // Attempt to open it
                try {
                    SerialPort port = (SerialPort) port_id.open("PortListOpen",20000);
                    System.out.println("Opened successfully:"+port);
                    try {
                        int baudRate = 9600; //
                        port.setSerialPortParams(
                                baudRate,SerialPort.DATABITS_7,SerialPort.STOPBITS_1,SerialPort.PARITY_EVEN);
                        port.setDTR(true);


                        port.setFlowControlMode(SerialPort.FLOWCONTROL_NONE);

                        System.out.println("properties are set");
                    } catch (UnsupportedCommOperationException e) {
                        System.out.println(e);
                    }
                    try {
                        //input = new SerialReader(in);
                        port.addEventListener(this);
                        System.out.println("listeners attached" + this);
                    } catch (TooManyListenersException e) {
                        System.out.println("too many listeners");
                    }
                    port.notifyOnDataAvailable(true);

                    //port.notifyOnOutputEmpty(true);
                    //sendMessage(port,"@PL");
                    //port.close ();
                    try {
                        is = new BufferedReader(new InputStreamReader(port.getInputStream()));
                    } catch (IOException e) {
                        System.err.println("Can't open input stream: write-only");
                        is = null;
                    }
                    try {
                        os = new PrintStream(port.getOutputStream(),true);
                    } catch (IOException ex) {
                        Logger.getLogger(openPort.class.getName()).log(Level.SEVERE,null,ex);
                    }

                    try {
                        inputStream = port.getInputStream();
                        System.out.println("inputstream" + inputStream.available());
                        outputStream = (OutputStream) port.getOutputStream();
                        os = new PrintStream(port.getOutputStream(),true,"US-ASCII");


                    } catch (IOException e) {
                        System.out.println(e);
                    }

                    //set the created variables to global variables
                    global_variables.port = port;
                    global_variables.inputStream = inputStream;
                    System.out.println(inputStream);
                    System.out.println(outputStream);
                    global_variables.outputStream = outputStream;
                    global_variables.os = os;
                } catch (PortInUseException pe) {
                    System.out.println("Open Failed");
                    String owner_name = port_id.getCurrentOwner();
                    if (owner_name == null) {
                        System.out.println("Port Owned by unidentified app");
                    } else // The owner name not returned correctly unless it is
                    // a Java program.
                    {
                        System.out.println("  " + owner_name);
                    }
                }
            }
        }
    }

    public static void sendMessage(SerialPort port,String msg) {
        if (port != null) {
                System.out.println(msg);
            try {
                byte[] bytes = msg.getBytes("US-ASCII");
                try {
                    global_variables.outputStream.write(bytes);
                    System.out.println(bytes.length);
                    global_variables.outputStream.flush();
                } catch (IOException ex) {
                    Logger.getLogger(openPort.class.getName()).log(Level.SEVERE,ex);
                }
            } catch (UnsupportedEncodingException ex) {
                Logger.getLogger(openPort.class.getName()).log(Level.SEVERE,ex);
            }
                System.out.println("Opened successfully:"+msg.getBytes());
                //global_variables.outputStream.write(msg.getBytes());
                //global_variables.outputStream.flush();
                //global_variables.os.print(msg);
                System.out.println(global_variables.outputStream);
                try {
                    Thread.sleep(2000);  // Be sure data is xferred before closing
                    System.out.println("read called");
                    //SimpleRead read = new SimpleRead();
                    //int read = global_variables.inputStream.read();
                    //System.out.println("read call ended"+read);
                } catch (Exception e) {
                }

        }
    }

    public void serialEvent(SerialPortEvent event) {
        System.out.println(event.getEventType());
        String line;
                try {
                    line = is.readLine();
                    if (line == null) {
                        System.out.println("EOF on serial port.");
                        System.exit(0);
                    }
                    os.println(line);
                } catch (IOException ex) {
                    System.err.println("IO Error " + ex);
                }
        switch (event.getEventType()) {
            /*
            case SerialPortEvent.BI:

            case SerialPortEvent.OE:

            case SerialPortEvent.FE:

            case SerialPortEvent.PE:

            case SerialPortEvent.CD:

            case SerialPortEvent.CTS:

            case SerialPortEvent.DSR:

            case SerialPortEvent.RI:


            case SerialPortEvent.OUTPUT_BUFFER_EMPTY:
            System.out.println("event.getEventType()");
            break;
             *
             */

            case SerialPortEvent.DATA_AVAILABLE:
                System.out.println("inside event handler data available");
                byte[] readBuffer = new byte[20];


                try {
                    while (inputStream.available() > 0) {
                        int numBytes = inputStream.read(readBuffer);
                    }
                    System.out.print(new String(readBuffer));
                    System.exit(1);
                } catch (IOException e) {
                    System.out.println(e);
                }

                break;
        }
    }
} // PortListOpen

I open the port on the main method and send a message on the button click event in the application

Solution

. Available () cannot be used for interprocess communication (including sequences) because it only checks whether data is available in the current process (in the input buffer)

In serial communication, when you send a message and immediately call available (), you will get most of 0 because the serial port has not replied to any data

The solution is to block read() in a separate thread (end it with interrupt()):

Thread interrupt not ending blocking call on input stream read