Develop Reference

Sending a String through socket. Server not receiving it

I've been struggling lately to find a way to deliver strings through a socket file. I'm planning to create a remote tool(client) to execute things based on the received message(server).
I've searched answers for my problem on google and i found some things and managed to understand things but I also got some problems (i'm new to programming, not yet in college).
I would appreciate any help in this matter
SocketService.java ---- class file = serverside
package socket;
import java.io.DataInputStream;
import java.io.EOFException;
import java.io.IOException;
import java.net.ServerSocket;
import java.net.Socket;
import java.net.UnknownHostException;
import java.util.concurrent.TimeUnit;
public class ServiceSocket {
static ServerSocket myService;
static Socket thesocket;
static Thread socketThread;
public static boolean socketRunning;
public static DataInputStream socketMessage;
public static void initialise(String localhost, int portNumber ){
// make a server socket//////
try {
myService = new ServerSocket(portNumber);
System.out.println();
} catch (IOException e) {
e.printStackTrace();
}
//////////////////////////////
}
public static void deploySocket(){
socketThread = new Thread() {
public void run(){
// making connection
System.out.println("VVaiting for connection...");
try {
thesocket = myService.accept();
System.out.println("Connection made");
socketRunning = true;
} catch (IOException e) {
e.printStackTrace();
}
////////////////////////////////////
try {
StartBrain();
} catch (IOException e1) {
e1.printStackTrace();
}
if(socketRunning = false) {
try {
thesocket.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
};
socketThread.start();
}
public static String getSocketMessage() throws IOException {
try {
socketMessage = new DataInputStream(thesocket.getInputStream());
} catch (IOException e1) {
e1.printStackTrace();
}
boolean looprunning = true;
String message = null;
System.out.println("entering loop");
do {
try {
while (socketMessage.readUTF() != null) {
message = socketMessage.readUTF();
looprunning = false;
}
} catch (EOFException e) {
}
}while(looprunning);
System.out.println("Message received from UTF: " + message);
System.out.println("loop exited vvith message");
if(message == null) {
message = "no message";
}
return message;
}
public static void StartBrain() throws IOException {
System.out.println("socket brain started");
String BrainMessage = getSocketMessage();
if(BrainMessage == "command") {
System.out.println("Command EXECUTED HAHA");
} else if(BrainMessage == "taskschedule") {
System.out.println("task scheduled");
} else {
System.out.println("no command received");
}
}
Main.java ----- class file = serverside
package main;
import socket.ServiceSocket;
public class Main {
public static void main(String[] args) {
ServiceSocket.initialise("localhost", 3535);
ServiceSocket.deploySocket();
}
}
}
Main.java = CLIENT
package mainPackage;
import java.io.*;
import java.net.*;
import java.util.concurrent.TimeUnit;
public class Main {
private static Socket clientSocket;
public static void sendMessage(String message) throws IOException, InterruptedException {
DataOutputStream dOut = new DataOutputStream(Main.clientSocket.getOutputStream());
dOut.writeUTF(message);
dOut.flush();
dOut.close();
}
public static void main(String[] args) throws Exception {
// String modifiedSentence;
clientSocket = new Socket("localhost", 3535);
System.out.println("Initializing");
sendMessage("command");
boolean running = true;
while(running) {
TimeUnit.SECONDS.sleep(3);
sendMessage("taskschedule");
}
clientSocket.close();
}
}
main problem
do {
try {
while (socketMessage.readUTF() != null) {
message = socketMessage.readUTF();
looprunning = false;
}
} catch (EOFException e) {
}
}while(looprunning);
it doesn't read the string/UTF

It does read it, here:
while (socketMessage.readUTF() != null) {
and then throws it away as you're not assigning the return-value to a variable, and then tries to read another one, here:
message = socketMessage.readUTF();
but the one (first) message you send is already gone.

You have problem in
while (socketMessage.readUTF() != null) {
message = socketMessage.readUTF();
looprunning = false;
}
First call to method readUTF() will block thread and read UTF string from socket, but you discard this value and try read string second time.
If you replace socketMessage.readUTF() != null with looprunning server will log this messages:
VVaiting for connection...
Connection made
socket brain started
entering loop
Message received from UTF: command
loop exited vvith message
no command received
P.S.
Command is not recognized because use compare objects (string is object) with ==, but you must use equals.
public static void StartBrain() throws IOException {
System.out.println("socket brain started");
String BrainMessage = getSocketMessage();
if (BrainMessage.equals("command")) {
System.out.println("Command EXECUTED HAHA");
} else if (BrainMessage.equals("taskschedule")) {
System.out.println("task scheduled");
} else {
System.out.println("no command received");
}
}
Server log:
VVaiting for connection...
Connection made
socket brain started
entering loop
Message received from UTF: command
loop exited vvith message
Command EXECUTED HAHA

Java Multithreading for IVRS with GSM Modem rxtx (playing voice file making event listener stop working)

I have implemented a program to receive call using gsm modem. Upon Detecting "RING" call is answered an audio clip is played by calling a function from inside DATA_AVAILABLE EVENT HANDLER. But the event handler stops working after this. After the audio is complete Event Handler does not show any data received event anymore.
Why does the event listener stops working. Am I doing it wrong by playing the audio from inside the event handler? I was thinking about setting a variable true or false from inside data_received event handler and create custom event handler to listen to change to that variable to do playback of audio can these both work simultaneously in anyway?
How to create a multi threading solution So that Serial I/O is not interrupted and Audio Playback and Audio Sampling Can be done in a synchronised manner to detect dtmf tones.
Is there any way that serial port events can be listened to constantly without interruption and run a function for audio sampling and audio playback at specific time
Call Accepted in this case of switch and thread is started inside play() function
case SerialPortEvent.DATA_AVAILABLE:
StringBuffer sb = new StringBuffer();
byte[] readBuffer = new byte[2048];
try {
while (inputStream.available() > 0)
{
int numBytes = inputStream.read(readBuffer);
sb.append(new String(readBuffer,0,numBytes));
System.out.println(numBytes);
System.out.println(sb);
}
System.out.println("Data Available");
if((sb.toString()).contains("RING")){
System.out.println("Enter Inside if RING Loop");
//play();
send("ATA\r\n");
//welcomeMessage();
}
if((sb.toString()).contains("CARRIER")){
hangup();
//Thread.sleep(1000);
closePort();
outCommand();
System.out.println("Enter Inside if NO CARRIER Loop");
}
//print response message
System.out.print(sb.toString());
} catch (IOException e) {
}
break;
public void play() {
try {
new Thread() {
public void run() {
for(int i=0;i<1;i++)
welcomeMessage();
}
}.start();
} catch (Throwable e) {
e.printStackTrace();
}
}
Full Code
package sample;
import java.io.*;
import java.util.*;
import javax.sound.sampled.*;
import javazoom.jl.player.*;
import java.io.FileInputStream;
import gnu.io.*;
import java.io.*;
import javax.sound.sampled.AudioInputStream;
import javax.sound.sampled.AudioSystem;
import javax.sound.sampled.Clip;
import javax.sound.sampled.LineUnavailableException;
import javax.sound.sampled.UnsupportedAudioFileException;
import org.apache.log4j.chainsaw.Main;
import sun.audio.*;
public class GSMConnect implements SerialPortEventListener,
CommPortOwnershipListener {
private static String comPort = "COM3"; // This COM Port must be connect with GSM Modem or your mobile phone
private String messageString = "";
private CommPortIdentifier portId = null;
private Enumeration portList;
private InputStream inputStream = null;
private OutputStream outputStream = null;
private SerialPort serialPort;
String readBufferTrial = "";
/** Creates a new instance of GSMConnect */
public GSMConnect(String comm) {
this.comPort = comm;
}
public boolean init() {
portList = CommPortIdentifier.getPortIdentifiers();
while (portList.hasMoreElements()) {
portId = (CommPortIdentifier) portList.nextElement();
if (portId.getPortType() == CommPortIdentifier.PORT_SERIAL) {
if (portId.getName().equals(comPort)) {
System.out.println("Got PortName");
return true;
}
}
}
return false;
}
public void checkStatus() {
send("AT+CREG?\r\n");
}
public void dial(String phoneNumber) {
try {
//dial to this phone number
messageString = "ATD" + phoneNumber + ";\r\n";
outputStream.write(messageString.getBytes());
System.out.println("Called ");
} catch (IOException e) {
e.printStackTrace();
}
}
public void send(String cmd) {
try {
outputStream.write(cmd.getBytes());
} catch (IOException e) {
e.printStackTrace();
}
}
public void sendMessage(String phoneNumber, String message) {
char quotes ='"';
send("AT+CMGS="+quotes + phoneNumber +quotes+ "\r\n");
try {
Thread.sleep(2000);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
// send("AT+CMGS=\""+ phoneNumber +"\"\r\n");
send(message + '\032');
System.out.println("Message Sent");
}
public void hangup() {
send("ATH\r\n");
}
public void welcomeMessage(){
// open the sound file as a Java input stream
String gongFile = "C:\\Users\\XXXX\\Desktop\\1-welcome.wav";
}*/
try{
FileInputStream fis = new FileInputStream("C:\\Users\\XXXX\\Desktop\\7001110.mp3");
Player playMP3 = new Player(fis);
playMP3.play();
System.out.print("welcomeMessage() Read");
}catch(Exception e){
System.out.println(e);
}
}
public void play() {
try {
new Thread() {
public void run() {
for(int i=0;i<1;i++)
welcomeMessage();
}
}.start();
} catch (Throwable e) {
e.printStackTrace();
}
}
public void connect() throws NullPointerException {
if (portId != null) {
try {
portId.addPortOwnershipListener(this);
serialPort = (SerialPort) portId.open("MobileGateWay", 2000);
serialPort.setSerialPortParams(115200,SerialPort.DATABITS_8,SerialPort.STOPBITS_1,SerialPort.PARITY_NONE);
} catch (PortInUseException | UnsupportedCommOperationException e) {
e.printStackTrace();
}
try {
inputStream = serialPort.getInputStream();
outputStream = serialPort.getOutputStream();
} catch (IOException e) {
e.printStackTrace();
}
try {
/** These are the events we want to know about*/
serialPort.addEventListener(this);
serialPort.notifyOnDataAvailable(true);
serialPort.notifyOnRingIndicator(true);
} catch (TooManyListenersException e) {
e.printStackTrace();
}
//Register to home network of sim card
send("ATZ\r\n");
} else {
throw new NullPointerException("COM Port not found!!");
}
}
public void serialEvent(SerialPortEvent serialPortEvent) {
System.out.println("serialPortEvent.getEventType()"+serialPortEvent.getEventType());
switch (serialPortEvent.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:
// System.out.println("Ringing");
if( serialPortEvent.getNewValue() )
{
System.out.println("Ring Indicator On");
}
else
{
System.out.println("Ring Indicator Off");
}
break;
case SerialPortEvent.OUTPUT_BUFFER_EMPTY:
case SerialPortEvent.DATA_AVAILABLE:
StringBuffer sb = new StringBuffer();
byte[] readBuffer = new byte[2048];
try {
while (inputStream.available() > 0)
{
int numBytes = inputStream.read(readBuffer);
sb.append(new String(readBuffer,0,numBytes));
System.out.println(numBytes);
System.out.println(sb);
}
System.out.println("Data Available");
if((sb.toString()).contains("RING")){
System.out.println("Enter Inside if RING Loop");
//play();
send("ATA\r\n");
//welcomeMessage();
}
if((sb.toString()).contains("CARRIER")){
hangup();
//Thread.sleep(1000);
closePort();
outCommand();
System.out.println("Enter Inside if NO CARRIER Loop");
}
//print response message
System.out.print(sb.toString());
} catch (IOException e) {
}
break;
}
}
public void outCommand(){
System.out.print(readBufferTrial);
}
public void ownershipChange(int type) {
switch (type) {
case CommPortOwnershipListener.PORT_UNOWNED:
System.out.println(portId.getName() + ": PORT_UNOWNED");
break;
case CommPortOwnershipListener.PORT_OWNED:
System.out.println(portId.getName() + ": PORT_OWNED");
break;
case CommPortOwnershipListener.PORT_OWNERSHIP_REQUESTED:
System.out.println(portId.getName() + ": PORT_INUSED");
break;
}
}
public void closePort(){
serialPort.close();
}
public static void main(String args[]) {
GSMConnect gsm = new GSMConnect(comPort);
if (gsm.init()) {
try {
System.out.println("Initialization Success");
gsm.connect();
Thread.sleep(5000);
gsm.checkStatus();
Thread.sleep(5000);
// System.out.println("Before Auto Answer");
// gsm.send("ATS0=5");
// gsm.dial("87XXXXXSS");
// Thread.sleep(7500);
// System.out.println("After Auto Answer set");
// gsm.sendMessage("8XXXXXS56", "Trial Success Call me");
// gsm.sendMessage("80XXXXS56", "Trial Success Call me");
// gsm.sendMessage("8XXXXSXS6", "Trial Success Call me");
// Thread.sleep(5000);
// gsm.sendMessage("+919XXXXXXS3", "Third Msg");
// Thread.sleep(1000);
// gsm.dial("9XXXXS773");
// gsm.dial("871XXXXS5");
// Thread.sleep(1000);
// gsm.welcomeMessage();
// Thread.sleep(1000);
// gsm.welcomeMessage();// for turning on Echo ATE1&W
// Thread.sleep(20000);
// welcomeMessage();
// gsm.hangup();
// Thread.sleep(1000);
// gsm.closePort();
// gsm.outCommand();
// System.exit(1);
} catch (Exception e) {
e.printStackTrace();
}
} else {
System.out.println("Can't init this card");
}
}
}

Short of spending a good amount of time reproducing your environment I can give you two suggestions on how you might look into this.
a) Place a try-catch Throwable around your entire handler--often throwing exceptions can break event dispatchers
B) print out a debug statement when you enter and exit your event handler and ensure they are paired and that you get an exit after your last enter--a thread locking up will sometimes stop future events from being dispatched.
By the way you have an empty catch statement in one place--those scare the crap out of me because they often mask problems in ways that can waste days of your time. If you absolutely know you want to silently eat an exception there and you expect that exception to occur enough that it would pollute your logs to log it, please put a comment saying so.

java rxtx SerialWriter issue

I am using RXTX to communicate between JAVA and a microcontroller.
This is the JAVA code for opening a connection, sending and receiving data
package app;
import gnu.io.CommPort;
import gnu.io.CommPortIdentifier;
import gnu.io.SerialPort;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
public class SerialCommunication1 {
private static SerialCommunication1 instance = null;
private static boolean coonected = false;
public static SerialCommunication1 getInstance(){
if(instance == null)
instance = new SerialCommunication1();
return instance;
}
private SerialCommunication1() {
super();
try {
connect("COM4");
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
SerialCommunication1.coonected = true;
}
void connect(String portName) throws Exception {
CommPortIdentifier portIdentifier = CommPortIdentifier
.getPortIdentifier(portName);
if (portIdentifier.isCurrentlyOwned()) {
System.out.println("Error: Port is currently in use");
} else {
CommPort commPort = portIdentifier.open(this.getClass().getName(),
2000);
if (commPort instanceof SerialPort) {
SerialPort serialPort = (SerialPort) commPort;
serialPort.setSerialPortParams(9600, SerialPort.DATABITS_8,
SerialPort.STOPBITS_2, SerialPort.PARITY_NONE);
InputStream in = serialPort.getInputStream();
OutputStream out = serialPort.getOutputStream();
(new Thread(new SerialReader(in))).start();
(new Thread(new SerialWriter(out))).start();
} else {
System.out
.println("Error: Only serial ports are handled by this example.");
}
}
}
/** */
public static class SerialReader implements Runnable {
InputStream in;
public SerialReader(InputStream in) {
this.in = in;
}
public void run() {
byte[] buffer = new byte[1024];
int len = -1;
try {
while ((len = this.in.read(buffer)) > -1) {
System.out.print(new String(buffer, 0, len));
}
} catch (IOException e) {
e.printStackTrace();
}
}
}
/** */
public static class SerialWriter implements Runnable {
OutputStream out;
static String str = null;
public SerialWriter(OutputStream out) {
this.out = out;
}
public void run() {
System.out.println("Will try to execute");
try {
if(str.length() > 0){
this.out.write(str.getBytes());
str = null;
}
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
And this is the Java code that is calling when an event triggers
SerialCommunication1.getInstance();
if(ledStatus == true) {SerialCommunication1.SerialWriter.str = "4A01";}
else {SerialCommunication1.SerialWriter.str = "4A00";}
stopProcess();
And now the problem. I need to send a command to my microcontroller with the code 4A01 and, after receiving the answer, I need to call it again with the code 4A00. The calls are triggered by a button from my Java interface. The problem is that the second call is not executed (4A00 is not sending). I tried to inverse the command codes and they work well. After the first one (4A01) is executed, my microcontroller reacts and sends the response which is read by java and my interface is updated. When I send the invers command (4A00) it stops exactly at this line SerialCommunication1.SerialWriter.str = "4A00"; and doesn't even enter inside the SerialWriter's run() method.
Do you have any idea why is this happening? From the side of my microcontroller there is no problem, I checked all the possibilities with a tool.
I hope I made myself clear.
Thank you!
LE: I forgot to tel you that it didn't throw any errors or exceptions

I'm not sure because I'm not able to test your code but I think your problem is in SerialWriter class:
public static class SerialWriter implements Runnable {
OutputStream out;
static String str = null; // Here str is initialized to null
public SerialWriter(OutputStream out) {
this.out = out;
}
public void run() {
System.out.println("Will try to execute");
try {
if(str.length() > 0) { // this should throw NPE because str is null
this.out.write(str.getBytes());
str = null;
}
} catch (IOException e) {
e.printStackTrace();
}
}
}
Since there is no loop in this method, then the thread created within SerialCommunication1 at this line:
(new Thread(new SerialWriter(out))).start();
most likely finishes its execution after sending the first str.
Honestly I don't understand how does it even send a single string, since str is initialized to null in first place and it should throw NullPointerException at str.length() line.
I would suggest you this approach:
Don't trigger a writer thread when connection is established, just trigger a new one every time a message will be sent.
Use Singleton pattern correctly.
Keep a reference to the serial port in SerialCommunication1 class.
Translated to code it would be something like this:
class SerialWriter implements Runnable {
OutputStream out;
String message;
public SerialWriter(OutputStream out) {
this.out = out;
}
public void setMessage(String msg) {
this.message = msg;
}
public void run() {
try {
if(message != null) {
this.out.write(str.getBytes());
}
} catch (IOException e) {
e.printStackTrace();
}
}
}
Then in SerialCommunication1 class add this public method:
public void sendMessage(String msg) {
SerialWriter writer = new SerialWriter(serialPort.getOutputStream()); // of course you'll have to keep reference to serialPort when connection is established
writer.setMessage(msg);
(new Thread(writer)).start();
}
And finally call this method in this way:
SerialCommunication1.getInstance().sendMessage("4A01");

tzortzik,
I think tha is a timeout problem. Try to addding a delay to writer :
/** */
public static class SerialWriter implements Runnable {
OutputStream out;
static String str = null;
public SerialWriter(OutputStream out) {
this.out = out;
}
public void run() {
Thread.sleep(500); //<----------- this should be in mainThread before to SerialWriter.start();
System.out.println("Will try to execute");
try {
if(str.length() > 0){
this.out.write(str.getBytes());
str = null;
}
} catch (IOException e) {
e.printStackTrace();
}
}
}
It happens to me many times, "we should learn to wait for a response" (^_^)
Check if you are executing well a secuence like the next:
Send command 4A01
Receive response 4A01 from micro
WAIT FOR RESPONSE BEFORE SEND SECOND COMMAND. Thread.sleep(500); //wait for 500 milis or more
Send command 4A00
Receive response 4A00 from micro
I hope it could help you.

Java/Arduino - Read data from the Serial Port

I've got a program in Java where I have to read the information that an Arduino is sending.
I took the Java code from here. Now, I didn't really understand how it works, but I tried to modify it and I got this:
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.OutputStream;
import gnu.io.CommPortIdentifier;
import gnu.io.SerialPort;
import gnu.io.SerialPortEvent;
import gnu.io.SerialPortEventListener;
import java.util.Enumeration;
public class Serial implements SerialPortEventListener {
SerialPort serialPort;
private static final String PORT_NAMES[] = {
"/dev/tty.usbserial-A9007UX1", // Mac OS X
"/dev/ttyUSB0", // Linux
"COM3", // Windows
};
private BufferedReader input;
private static OutputStream output;
private static final int TIME_OUT = 2000;
private static final int DATA_RATE = 115200;
public void initialize() {
CommPortIdentifier portId = null;
Enumeration portEnum = CommPortIdentifier.getPortIdentifiers();
while (portEnum.hasMoreElements()) {
CommPortIdentifier currPortId = (CommPortIdentifier) portEnum.nextElement();
for (String portName : PORT_NAMES) {
if (currPortId.getName().equals(portName)) {
portId = currPortId;
break;
}
}
}
if (portId == null) {
System.out.println("Could not find COM port.");
return;
}
try {
serialPort = (SerialPort) portId.open(this.getClass().getName(),TIME_OUT);
serialPort.setSerialPortParams(DATA_RATE, SerialPort.DATABITS_8, SerialPort.STOPBITS_1, SerialPort.PARITY_NONE);
input = new BufferedReader(new InputStreamReader(serialPort.getInputStream()));
output = serialPort.getOutputStream();
serialPort.addEventListener(this);
serialPort.notifyOnDataAvailable(true);
}
catch (Exception e) {
System.err.println(e.toString());
}
}
public synchronized void serialEvent(SerialPortEvent oEvent) {
if (oEvent.getEventType() == SerialPortEvent.DATA_AVAILABLE) {
try {
String inputLine=input.readLine();
System.out.println(inputLine);
} catch (Exception e) {
System.err.println(e.toString());
}
}
}
public synchronized void close() {
if (serialPort != null) {
serialPort.removeEventListener();
serialPort.close();
}
}
public Serial(String ncom){
if(Integer.parseInt(ncom)>=3 && Integer.parseInt(ncom)<=9)
PORT_NAMES[2] = "COM" + ncom;
initialize();
Thread t=new Thread() {
public void run() {
try {Thread.sleep(1000000);} catch (InterruptedException ie) {}
}
};
t.start();
System.out.println("Serial Comms Started");
}
public synchronized void send(int b){
try{
output.write(b);
}
catch (Exception e) {
System.err.println(e.toString());
}
}
public synchronized int read(){
int b = 0;
try{
b = (int)input.read();
}
catch (Exception e) {
System.err.println(e.toString());
}
return b;
}
}
I create the object Serial with the COM port I need in the main program, then I use Serial.read and Serial.write when I need it.
Serial.write works great, Arduino gets the data and show it in a LCD Display. The problem is Serial.read. When the program is running, it keep read from serial port (around every 40 ms), but that doesn't mean Arduino sent something. Arduino sends a byte only when a button is pushed. So, when the Java code is running, it throws "n" Exception before read something, and this couses so much lag.
I know I need something like Serial.available(), I tried input.available(), but it doesn't work. I don't know how to solve this problem.
If you have a code that working, I'd be so much grateful if you could give it to me. I just need two methods, read and write, I don't care how the code works :D
EDIT:
I changed the Serial class, now it has again this method as apremalal said
public synchronized void serialEvent(SerialPortEvent oEvent) {
if (oEvent.getEventType() == SerialPortEvent.DATA_AVAILABLE) {
try {
String inputLine=null;
if (input.ready()) {
inputLine = input.readLine();
panel.read(inputLine);
}
} catch (Exception e) {
System.err.println(e.toString());
}
}
}
and in the other class (Panel in this case) I've got this:
public void read(String data){
System.out.println(data);
System.out.println(data == "255");
if(data == "255")
//code here
}
It print the values correctly but data == "255" is always false, even if I really get a 255
....I tried to do Integer.parseInt but nothing changed. Why the hell?
EDIT 2: Ok solved :\
public void read(String data){
serialRead = Integer.parseInt(data);
if(serialRead == 255)
//code here
}
Now it's work..don't know why I had to do this... meh whatever :)

You don't want to specifically write a read function it's already there in the sample code.As TheMerovingian pointed out you can check the input Buffer before reading.Here is the working code which I have used in one of my projects.
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.OutputStream;
import gnu.io.CommPortIdentifier;
import gnu.io.SerialPort;
import gnu.io.SerialPortEvent;
import gnu.io.SerialPortEventListener;
import java.util.Enumeration;
public class SerialTest implements SerialPortEventListener {
SerialPort serialPort;
/** The port we're normally going to use. */
private static final String PORT_NAMES[] = { "/dev/tty.usbserial-A9007UX1", // Mac OS X
"/dev/ttyUSB0", // Linux
"COM35", // Windows
};
private BufferedReader input;
private OutputStream output;
private static final int TIME_OUT = 2000;
private static final int DATA_RATE = 9600;
public void initialize() {
CommPortIdentifier portId = null;
Enumeration portEnum = CommPortIdentifier.getPortIdentifiers();
//First, Find an instance of serial port as set in PORT_NAMES.
while (portEnum.hasMoreElements()) {
CommPortIdentifier currPortId = (CommPortIdentifier) portEnum.nextElement();
for (String portName : PORT_NAMES) {
if (currPortId.getName().equals(portName)) {
portId = currPortId;
break;
}
}
}
if (portId == null) {
System.out.println("Could not find COM port.");
return;
}
try {
serialPort = (SerialPort) portId.open(this.getClass().getName(),
TIME_OUT);
serialPort.setSerialPortParams(DATA_RATE,
SerialPort.DATABITS_8,
SerialPort.STOPBITS_1,
SerialPort.PARITY_NONE);
// open the streams
input = new BufferedReader(new InputStreamReader(serialPort.getInputStream()));
output = serialPort.getOutputStream();
serialPort.addEventListener(this);
serialPort.notifyOnDataAvailable(true);
} catch (Exception e) {
System.err.println(e.toString());
}
}
public synchronized void close() {
if (serialPort != null) {
serialPort.removeEventListener();
serialPort.close();
}
}
public synchronized void serialEvent(SerialPortEvent oEvent) {
if (oEvent.getEventType() == SerialPortEvent.DATA_AVAILABLE) {
try {
String inputLine=null;
if (input.ready()) {
inputLine = input.readLine();
System.out.println(inputLine);
}
} catch (Exception e) {
System.err.println(e.toString());
}
}
// Ignore all the other eventTypes, but you should consider the other ones.
}
public static void main(String[] args) throws Exception {
SerialTest main = new SerialTest();
main.initialize();
Thread t=new Thread() {
public void run() {
//the following line will keep this app alive for 1000 seconds,
//waiting for events to occur and responding to them (printing incoming messages to console).
try {Thread.sleep(1000000);} catch (InterruptedException ie) {}
}
};
t.start();
System.out.println("Started");
}
}
EDIT : serialEvent function is responsible for reading the buffer.
public synchronized void serialEvent(SerialPortEvent oEvent) {
if (oEvent.getEventType() == SerialPortEvent.DATA_AVAILABLE) {
try {
String inputLine=null;
if (input.ready()) {
inputLine = input.readLine();
System.out.println(inputLine);
}
} catch (Exception e) {
System.err.println(e.toString());
}
}
// Ignore all the other eventTypes, but you should consider the other ones.
}

The BufferedReader class has a ready() method that returns True if "the buffer is not empty, or if the underlying character stream is ready." and False otherwise. So you could add a check in the read() method to make sure there is data to be read before trying to read.
public synchronized int read(){
int b = 0;
try{
if (input.ready()) {
b = (int)input.read();
}
}catch (Exception e) {
System.err.println(e.toString());
}
return b;
}
It looks like the code has a try-catch in place to handle if those things fail, which is possibly what causes your lag because try-catch are quite expensive. So the input.ready() check should result in fewer exceptions.

inputstream.available() is 0 always

I have no idea of what is happening to my code. i am getting no errors and no response as well. I am writing the data to the serialport and waiting for the response by activating port.notifyOnDataAvailable(true); but this event is not triggered and inputstream.available() returns 0 always. What might be wrong ? I am using 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, null, ex);
}
} catch (UnsupportedEncodingException ex) {
Logger.getLogger(openPort.class.getName()).log(Level.SEVERE, null, 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 am opening the port on main method and sending the message on a button click event inside the application.

.available() can not be used in inter-process communication (serial included), since it only checks if there is data available (in input buffers) in current process.
In serial communication, when you send a messaga and then immediately call available() you will mostly get 0 as serial port did not yet reply with any data.
The solution is to use blocking read() in a separate thread (with interrupt() to end it):
Thread interrupt not ending blocking call on input stream read

To partially answer your question.
From the javadocs
The available method for class
InputStream always returns 0.
http://download.oracle.com/javase/6/docs/api/java/io/InputStream.html#available()
So that part at least is as expected

By using a PrintStream you are suppressing exceptions that you need to know about in any request/response scenario.
Most probably you haven't even sent anything yet.