Reading bluetooth GPS data from a Nokia phone

Question

I have a problem reading data from a MTK bluetooth GPS device from a Nokia phone (7610, Symbian S60).
I wrote a midlet (my phone supports CLDC 1.0/MIDP 2.0) that create a thread to read data
from the device (using RFCOMM protocol), the code is:
package gpsreader.bluetooth;
import javax.microedition.io.*;
import java.io.*;
public class BTrxtx implements Runnable {
private String url = ""; // Connection string to the bluetooth device.
private boolean canRead; // True if possible to read from device.
private boolean canWrite; // True if possible to write to device.
private String btstr = ""; // Last received string.
private int strCounter;
private int byteCounter;
private StreamConnection conn = null;
private InputStream inputstream = null;
private OutputStream outputstream = null;
private boolean newStr;
private static final char[] EOL_BYTES = {'\015','\012'};
public BTrxtx(String u) {
url = u;
canRead = false;
canWrite = false;
strCounter = 0;
byteCounter = 0;
newStr = false;
Thread t = new Thread(this);
t.start();
private void openInput() {
canRead = false;
try {
inputstream = conn.openInputStream();
canRead = true;
}catch(Exception e) {
setBtstr("oin");
System.out.println(e);
private void openOutput() {
canWrite = false;
try {
outputstream = conn.openOutputStream();
canWrite = true;
}catch(Exception e) {
setBtstr("oout");
System.out.println(e);
private void openConn() {
try {
conn = (StreamConnection) Connector.open(url);
openInput();
openOutput();
}catch(Exception e) {
setBtstr("oconn");
System.out.println("Failed to open connection: " + e);
private void closeInput() {
try {
if(inputstream!=null) {
inputstream.close();
}catch(Exception e) {
setBtstr("cin");
System.out.println(e);
private void closeOutput() {
try {
if(outputstream!=null) {
outputstream.close();
}catch(Exception e) {
setBtstr("cout");
System.out.println(e);
private void closeConn() {
try {
closeInput();
closeOutput();
if(conn!=null) {
conn.close();
}catch(Exception e) {
setBtstr("cconn");
System.out.println(e);
public void run() {
openConn();
try {
Thread.sleep(200);
}catch(Exception e) {
try {
int i = 0;
char c;
String s = "";
// Start reading the data from the GPS
while(canRead==true) {
i = inputstream.read(); // read one byte at the time.
if(i==-1) {
closeConn();
try {
Thread.sleep(200);
}catch(Exception e) {
openConn();
try {
Thread.sleep(200);
}catch(Exception e) {
continue;
byteCounter++;
// Every sentence starts with a '$'
if(i==36){
if(s.length()>0) {
strCounter++;
setBtstr(s);
s = "";
c = (char) i;
s += c;
System.out.println("GPS return no data");
setBtstr("BTend");
}catch(Exception e){
setBtstr("BTrun");
System.out.println(e);
private String byte2hex(byte b) {
char[] alphaHex = {'0', '1', '2', '3',
'4', '5', '6', '7',
'8', '9', 'A', 'B',
'C', 'D', 'E', 'F',
int low = (int) b & 0x0f;
int hi = (int) (b & 0xf0) >> 4;
String res = String.valueOf(alphaHex[hi]) + String.valueOf(alphaHex[low]);
return res;
public boolean sendData(String data) {
boolean res = false;
try {
if((canWrite==true) && (conn!=null) && (outputstream!=null) && (data!=null)){
StringBuffer rec = new StringBuffer(256);
// Calculate checksum
int index = data.length();
byte checksum = 0;
while(--index>=0) {
checksum ^= (byte) data.charAt(index);
rec.setLength(0);
rec.append('$');
rec.append(data);
rec.append('*');
rec.append(byte2hex(checksum));
System.out.println(">"+rec.toString());
rec.append(EOL_BYTES);
outputstream.write(rec.toString().getBytes());
}catch(Exception e) {
System.out.println(e);
return res;
public int getStrCounter() {
return strCounter;
public int getByteCounter() {
return byteCounter;
public String getBtstr() {
newStr = false;
return btstr;
private void setBtstr(String s) {
newStr = true;
btstr = s;
public boolean receivedData() {
return newStr;
The problem is on method "run" at line:
     i = inputstream.read(); // read one byte at the time.
after reading some data (usually one NMEA string) read method returns -1,
and even if I try to close the connection and re-open it, after some other data is read,
the midlet is terminated by the phone with an error (something like "jes-13c-java-comms@1441adE32USER-CBase 40").
The GPS receiver is working, since from my PC I am able to connect with a bluetooth USB dongle and read outputs using RFCOMM.
Thx for any suggestions,
LB.

Answer 1

Work around.
I can not say I solved it, but I managed to get a work around:
I read in another post that there are some problems in thread handling on Nokia phones, so I rewrote the class so that it runs on the main thread and now it seems to work (I can not update the screen while reading from the device, but this isn't a big issue for me).
Just in case anyone is interested here is the final code:
import javax.microedition.io.*;
import java.io.*;
public class BTBrxtx {
private String url = ""; // Connection string to the bluetooth device.
private boolean canRead; // True if possible to read from device.
private String btstr = ""; // Last received string.
private int strCounter;
private int byteCounter;
private StreamConnection conn = null;
private InputStream inputstream = null;
private boolean newStr;
private String s = "";
private static final char[] EOL_BYTES = {'\015','\012'};
public BTBrxtx(String u) {
url = u;
canRead = false;
canWrite = false;
strCounter = 0;
byteCounter = 0;
newStr = false;
openConn();
try {
Thread.sleep(200);
}catch(Exception e) {
private void openInput() {
canRead = false;
try {
inputstream = conn.openInputStream();
canRead = true;
}catch(Exception e) {
setBtstr("oin");
System.out.println(e);
private void openConn() {
try {
conn = (StreamConnection) Connector.open(url);
openInput();
}catch(Exception e) {
setBtstr("oconn");
System.out.println("Failed to open connection: " + e);
private void closeInput() {
try {
if(inputstream!=null) {
inputstream.close();
}catch(Exception e) {
setBtstr("cin");
System.out.println(e);
private void closeConn() {
try {
closeInput();
if(conn!=null) {
conn.close();
}catch(Exception e) {
setBtstr("cconn");
System.out.println(e);
public void readInput() {
try {
int i = 0;
char c;
// Start reading the data from the GPS
while(canRead==true) {
i = inputstream.read(); // read one byte at the time.
if(i==-1) {
closeConn();
try {
Thread.sleep(200);
}catch(Exception e) {
openConn();
try {
Thread.sleep(200);
}catch(Exception e) {
continue;
byteCounter++;
// Every sentence starts with a '$'
if(i==36){
if(s.length()>0) {
strCounter++;
setBtstr(s);
s = "";
c = (char) i;
s += c;
return;
c = (char) i;
s += c;
System.out.println("GPS return no data");
setBtstr("BTend");
}catch(Exception e){
setBtstr("BTrun");
System.out.println(e);
private String byte2hex(byte b) {
char[] alphaHex = {'0', '1', '2', '3',
'4', '5', '6', '7',
'8', '9', 'A', 'B',
'C', 'D', 'E', 'F',
int low = (int) b & 0x0f;
int hi = (int) (b & 0xf0) >> 4;
String res = String.valueOf(alphaHex[hi]) + String.valueOf(alphaHex[low]);
return res;
public int getStrCounter() {
return strCounter;
public int getByteCounter() {
return byteCounter;
public String getBtstr() {
newStr = false;
return btstr;
private void setBtstr(String s) {
newStr = true;
btstr = s;
public boolean receivedData() {
return newStr;
Now I call method readInput in the main thread and than use getBtstr to retrieve data.
I'm still interested to know if someone had similar problems and how they have been solved.
Thx