Reading plain text from RFID tag

[DixieFlatline]

Hello!
I created Mifare1k tag with nfc manager. i wrote some plain text on it. How should i read it?
I tried the code below(modified one other example), bui it crashes my emulator as i run it (nokia 6212 classic). Do you have any piece of code that works?


public class Kartar extends MIDlet implements TargetListener,
NDEFRecordListener, CommandListener {

private DiscoveryManager dm;

private Form form;

/**
* Read command to set application to reading mode
*/
private Command readCommand;

/**
* Write command to set application to writing mode
*/
private Command writeCommand;

/**
* Exit command
*/
private Command exitCommand;

/**
* Boolean telling if application is in read mode,
*/
private boolean read = true;

protected void startApp() throws MIDletStateChangeException {
dm = DiscoveryManager.getInstance();

try {
// Register NDEF tag to target listener..
dm.addTargetListener(this, TargetType.NDEF_TAG);
// ..and png image mime type to NDEF record listener.
dm.addNDEFRecordListener(this, new NDEFRecordType(
NDEFRecordType.MIME, "text/plain"));
} catch (IllegalStateException e) {
form.append(e.toString());
} catch (ContactlessException e) {
form.append(e.toString());
}

// Initialize UI
form = new Form("Reading Mode");
readCommand = new Command("Read", Command.OK, 1);
exitCommand = new Command("Exit", Command.EXIT, 1);
form.addCommand(writeCommand);
form.addCommand(exitCommand);
form.setCommandListener(this);
Display.getDisplay(this).setCurrent(form);
}

protected void pauseApp() {
}

protected void destroyApp(boolean arg0) throws MIDletStateChangeException {
}

/**
* Notified when NDEF tag detected
*/
public void targetDetected(TargetProperties[] properties) {
// If application is not in read mode - write image to tag
if (!read) {
NDEFTagConnection conn = null;
try {
// Open connection to NDEF tag
conn = (NDEFTagConnection) Connector.open(properties[0]
.getUrl());

ByteArrayOutputStream baos = getImage("/com/nokia/test/simple/ndef/res/Smiley.png");

// Create NDEF Record to be added to NDEF Message
NDEFRecord recordToWrite = new NDEFRecord(new NDEFRecordType(
NDEFRecordType.MIME, "image/png"), null, baos
.toByteArray());

// Create NDEF Message and add created record in it.
NDEFMessage write_container = new NDEFMessage();
write_container.appendRecord(recordToWrite);

// Write NDEF Message to tag
conn.writeNDEF(write_container);

form.append("Image written");

} catch (IOException e) {
form.append(e.toString());
} catch (Exception e) {
form.append(e.toString());
} finally {
try {
if (conn != null) {
conn.close();
}
} catch (IOException e) {
form.append(e.toString());
}
}
}
}


/**
* proper NDEF message detected
*/
public void recordDetected(NDEFMessage mes) {
// If application is in read mode - show image from tag
if (read) {
// Get png image record from NDEF message
NDEFRecord rec[] = mes.getRecord(new NDEFRecordType(
NDEFRecordType.MIME, "text/plain"));

byte znaki []=rec[0].getPayload();
String s=new String(znaki);
displayAlert("Prebral sem: " + s, AlertType.INFO);

}
}

public void commandAction(Command c, Displayable d) {
if(c == exitCommand){
notifyDestroyed();
}
}

private void displayAlert(String error, AlertType type) {
Alert err = new Alert(form.getTitle(), error, null, type);
Display.getDisplay(this).setCurrent(err, form);
}

/**
* Read image from phone to ByteArrayOutputStream
*/
private ByteArrayOutputStream getImage(String s) throws IOException {
InputStream is = getClass().getResourceAsStream(s);
ByteArrayOutputStream baos = new ByteArrayOutputStream();
int c;
while ((c = is.read()) != -1) {
baos.write(c);
}
return baos;
}
}

Tnx

[mroland]

Hallo,

I created Mifare1k tag with nfc manager. i wrote some plain text on it. How should i read it?

That depends on what type of tag-content you created:
* If you created an NDEF tag (based on MIFARE 1K) with an NDEF record that has the MIME media type text/plain or
* if you created an NDEF tag (based on MIFARE 1K) with an NDEF Text record:
You can either use an NDEFRecordListener to listen for the expected type of record or you can use a TargetListener to listen for any NDEF tag and then parse its NDEF message for the expected record.
* If you created a MIFARE 1K tag and then directly edited its contents in the hex editor window without using the NDEF format:
In this case you need to access the MIFARE tag through Nokia's MIFARE API (see package com.nokia.nfc.nxp.mfstd).

I tried the code below(modified one other example), bui it crashes my emulator as i run it (nokia 6212 classic). Do you have any piece of code that works?

Your code looks OK, except that you don't need large portions of it. One thing I found is the line

form.addCommand(writeCommand);

In this line you use the uninitialized variable writeCommand. In my opinion this should lead to a NULL pointer exception, but it should not crash the emulator.

From your code I would guess that you have created an NDEF tag with an NDEF record of the MIME media type text/plain. So the easiest way to access (read-only) your NDEF record would be an NDEFRecordListener like this:

  public void startApp() {
    dm = DiscoveryManager.getInstance();
    
    try {
      dm.addNDEFRecordListener(this, new NDEFRecordType(NDEFRecordType.MIME, "text/plain"));
    } catch (Exception e) { }
    
    form = new Form("Reading Mode");
    exitCommand = new Command("Exit", Command.EXIT, 1);
    form.addCommand(exitCommand);
    form.setCommandListener(this);
    Display.getDisplay(this).setCurrent(form);
  }

  public void recordDetected(NDEFMessage msg) {
    if (msg != null) {
      for (int i = 0; i < msg.getNumberOfRecords(); ++i) {
        NDEFRecord rec = msg.getRecord(i);
        
        String recT = rec.getRecordType().getName();
        String recP = "";
        if (rec.getPayloadLength() > 0) {
          byte[] payload = rec.getPayload();
          
          try {
            for (int ll = 0; ll < payload.length; ++ll) {
              if (((payload[ll] >=  0) && (payload[ll] <=  8)) ||
                  ((payload[ll] >= 14) && (payload[ll] <= 31))) {
                payload[ll] = 46;
              }
            }
            
            recP = new String(payload, "ISO8859-1");
          } catch (Exception e) { }
        }

        form.append("Record " + i + ":\n"
            + (recT != null ? "TYPE=" + recT + "\n" : "")
            + "--- BEGIN DATA ---\n" + recP + "\n--- END DATA ---\n\n");
      }
    }
  }

Of course, you should also remove any unused NDEFRecordListener as soon as you no longer need it.


br,
Michael