For information about the design and functionality of the MIDlet, see section Design.
To create the MIDlet:
Create the URLWriter.java class file.
Import the required classes and packages.
// Classes for contactless communication import java.io.IOException; import javax.microedition.contactless.ContactlessException; import javax.microedition.contactless.DiscoveryManager; import javax.microedition.contactless.TargetListener; import javax.microedition.contactless.TargetProperties; import javax.microedition.contactless.TargetType; // Classes for NDEF targets import javax.microedition.contactless.ndef.NDEFMessage; import javax.microedition.contactless.ndef.NDEFRecord; import javax.microedition.contactless.ndef.NDEFRecordType; import javax.microedition.contactless.ndef.NDEFTagConnection; import javax.microedition.io.Connector; // Classes for UI import javax.microedition.lcdui.Alert; import javax.microedition.lcdui.AlertType; import javax.microedition.lcdui.Command; import javax.microedition.lcdui.CommandListener; import javax.microedition.lcdui.Display; import javax.microedition.lcdui.Displayable; import javax.microedition.lcdui.Form; import javax.microedition.midlet.*;
Set URLWriter to extend MIDlet and to implement TargetListener and CommandListener. Create the required variables.
public class URLWriter
extends MIDlet
implements TargetListener, CommandListener {
// Global variables for the UI
private Command exitCommand;
private Form form;Create the URLWriter class constructor.
public URLWriter() {Set up the MIDlet UI.
exitCommand = new Command("Exit", Command.EXIT, 1);
form = new Form("URLWriter");
form.addCommand(exitCommand);
form.setCommandListener(this);
form.append("Touch tag to write URL: \"www.developer.nokia.com\"");Register the MIDlet to receive notifications when NDEF targets are detected.
// Determine the contactless target types supported by the device
TargetType[] supportedTargetTypes = DiscoveryManager.getSupportedTargetTypes();
// Check if the NDEF_TAG type is supported by the device,
// and, if it is, register TargetListener for it
for (int i=0; i<supportedTargetTypes.length; i++) {
if (supportedTargetTypes[i].equals(TargetType.NDEF_TAG)) {
// Register TargetListener (this) for NDEF targets
try {
DiscoveryManager dm = DiscoveryManager.getInstance();
dm.addTargetListener(this, TargetType.NDEF_TAG);
} catch (SecurityException se) {
displayAlert("Unable to register TargetListener: " + se.toString(), AlertType.ERROR);
} catch (ContactlessException ce) {
displayAlert("Unable to register TargetListener: " + ce.toString(), AlertType.ERROR);
} catch (IllegalStateException ise) {
displayAlert("Unable to register TargetListener: " + ise.toString(), AlertType.ERROR);
} catch (NullPointerException npe) {
displayAlert("Unable to register TargetListener: " + npe.toString(), AlertType.ERROR);
}
// Break the loop, since a matching target type has been found
break;
}
}
}Create the mandatory MIDlet lifecycle methods. The MIDlet uses
the startApp method to display the UI.
public void startApp() {
Display.getDisplay(this).setCurrent(form);
}
public void pauseApp() {
}
public void destroyApp(boolean unconditional) {
}The targetDetected method of the TargetListener interface is called every time the device detects one or more NDEF
targets. The MIDlet uses the targetProperties array
returned by the method to open an NDEF connection to the target.
The custom getNDEFTAGConnection method
is used to retrieve the first applicable connection, an NDEF connection,
from the set of connections returned in the targetProperties array.
/**
* Implements the callback function of TargetListener
* @param targetProperties: Array of targets found by the device
*/
public void targetDetected(TargetProperties[] targetProperties) {
// In case no targets are found, exit the method
if (targetProperties.length == 0) {
return;
}
// NDEF connection for write operation
NDEFTagConnection ndconn = getNDEFTAGConnection(targetProperties);
try {
// Header byte: open bookmark in browser
byte[] headerByte = {0x00};
// Payload text: URL as a byte array
byte[] urlBytes = "http://www.developer.nokia.com/".getBytes();
// Create an NDEF record of type urn:nfc:wkt:U (a URI record)
// using the NFC Forum Record Type Description syntax
NDEFRecord r = new NDEFRecord(new NDEFRecordType(NDEFRecordType.NFC_FORUM_RTD, "urn:nfc:wkt:U"), null, null);
// Append payload manually
r.appendPayload(headerByte);
r.appendPayload(urlBytes);
// Create record array and add record
NDEFRecord[] myRecArray = new NDEFRecord[]{r};
// Generate a message out of the array
NDEFMessage myMessage = new NDEFMessage(myRecArray);
// Write message to tag
ndconn.writeNDEF(myMessage);
displayAlert("Information written", AlertType.INFO);
} catch (IOException io) {
displayAlert("Writing failed, please try again.", AlertType.ERROR);
} catch (ContactlessException io) {
displayAlert("ContactlessException during writeNDEF(): " + io.toString(), AlertType.ERROR);
} catch (Exception e) {
displayAlert("Exception: " + e.toString(), AlertType.ERROR);
} // In case of an exception, close connection properly
finally {
// Close connection again
if (ndconn != null) {
try {
ndconn.close();
} catch (IOException ex) {
displayAlert("IOException during close(): " + ex.toString(), AlertType.ERROR);
}
}
}
}
private NDEFTagConnection getNDEFTAGConnection(TargetProperties[] tProp) {
for (int j = 0; j < tProp.length; j++) {
Class[] connections = tProp[j].getConnectionNames();
if (connections != null) {
for (int i = 0; i < connections.length; i++) {
if (connections[i].getName().equals(
"javax.microedition.contactless.ndef.NDEFTagConnection")) {
try {
return (NDEFTagConnection) Connector.open(tProp[j].getUrl(connections[i]));
} catch (Exception e) {
displayAlert("Error writing NDEF: " + e.toString(), AlertType.ERROR);
}
}
}
}
}
return null;
}Implement command and message handling for the MIDlet UI. The
MIDlet uses the commandAction method to handle the
exit command, which involves unregistering TargetListener and closing the MIDlet. The MIDlet uses the displayAlert method to display error and other messages through the MIDlet UI.
/**
* Implements the callback function of CommandListener
* @param command: Command given
* @param displayable: Associated Displayable object
*/
public void commandAction(Command command, Displayable displayable) {
if (command == exitCommand) {
DiscoveryManager dm = DiscoveryManager.getInstance();
dm.removeTargetListener(this, TargetType.NDEF_TAG);
destroyApp(false);
notifyDestroyed();
}
}
private void displayAlert(String error, AlertType type) {
Alert err = new Alert(form.getTitle(), error, null, type);
Display.getDisplay(this).setCurrent(err, form);
}
}