Category: Java

This page was last modified 11:55, 24 December 2007.

From Forum Nokia Wiki

Contactless Communication API (JSR 257) defines a Java ME optional package that allows developer to access contactless communication, bi-directional communication and accessing read-only information using differente technologies via short-range wireless means, such as RFID or barcodes, infrared light, or even Bluetooth, and presents such devices via a simple, homogeneous interface to Java applications.

RFID in Brief
• RFID (Radio Frequency IDentification) is a
technology to carry information over short range
by radio waves
• 13.56 MHz frequency used in mobile devices
• A tag (transponder) contains digital information
in a microchip
• A reader communicates with a tag
• Two types of tags
• Active tag has own power source and longer distance
• Passive tag gets power from the incoming signal

NFC and NFC Forum
• NFC (Near Field Communication) specifies
simple wireless communication between close
coupled devices
• NFC enables
• Establishing other types of wireless communication
between devices
• Compatibility with existing contactless smart cards
• NFC Forum defines common protocols for basic
links between NFC enabled devices
• NFC Forum Data Exchange Format (NDEF)
provides vendor independent structure for data

Visual Tags in Brief
• Optically machine readable information on printed
material, typically in the form of bar codes or
data matrices
• Widely used in product identification
• Symbology defines the features of the visual tag
• Used character set
• Encoding and decoding rules
• Data size
• Error checking
• Printing requirements
• Over 200 known symbologies, only few widely used
• UPC / EAN / JAN in article numbering

Use Cases for JSR 257
• Read a URL to movie web page from a tag
• Store personal shortcuts like phone numbers
to a tag
• Bluetooth or WLAN connection initiation in a
multiplayer game with RFID communication
• Set device access point settings from a tag
• Field force on-the-job reporting using RFID tags
• Data gathering from RFID tags to a server

Registering for Target Discovery
// Get DiscoveryManager instance and set TargetListener
// for NDEF_TAG target
DiscoveryManager dm = DiscoveryManager.getInstance();
try {
dm.addTargetListener(this, TargetType.NDEF_TAG);
}
catch (ContactlessException ce) {
// handle exception
}

Registering for NDEF
Record Discovery
// Get DiscoveryManager instance and set TargetListener
// for NDEF_TAG and NFC_PEER targets
DiscoveryManager dm = DiscoveryManager.getInstance();
try {
NDEFRecordType recordType = new NDEFRecordType(
NDEFRecordType.NFC_FORUM_RTD,
"MyOwnType");
dm.addNDEFRecordListener(this, recordType);
}
catch (. . .) {
// handle exception
}

Making a Connection to the Target
public void targetDetected(TargetProperties[] prop) {
// Select first target
TargetProperties target = prop[0];
try {
// NDEF_TAG target found
String url = target.getUrl();
// Open NDEFTagConnection to the target
conn = (NDEFTagConnection)Connector.open(url);
// Read data from the target
NDEFMessage message = conn.readNDEF();
NDEFRecord[] records = message.getRecords();
. . .
}
catch (. . .) {
}
}

Receive Read-Only Data from NDEF Tag
public class MyMIDlet extends MIDlet implements
NDEFRecordListener {
public void recordDetected(NDEFMessage ndefMessage) {
NDEFRecord[] records = ndefMessage.getRecords();
for (int i=0; i<records.length; i++) {
// Handle data
}
}
}

Read Visual Tag Image
public void readVisualTag() {
checkReadSymbologySupport();
try {
String[] images =
SymbologyManager.getImageClasses();
// Open connection to visual tag
VisualTagConnection conn = (VisualTagConnection)
Connector.open("vtag://");
String data = conn.readVisualTag(getImage(),
images[0], mySymbology);
// Handle data from the image
conn.close();
}
catch (. . .) {
// handle exception
}
}

Generate Visual Tag Image
public void generateVisualTag() {
checkReadSymbologySupport();
try {
// Get properties for symbology
ImageProperties properties =
SymbologyManager.getImageProperties(“code-39”);
String imageClass = getImageClass();
VisualTagConnection conn = (VisualTagConnection)
Connector.open("vtag://");
// Generate visual tag image
Object vtagImage = conn.generateVisualTag(
"test", imageClass, properties);
. . .
}
catch (. . .) {
// handle exception
}
}

Summary
• JSR 257 offers communication to various contactless targets
• Can be extended to cover future contactless targets
• Provides general discovery mechanism
• Eases tasks of the application developer
• Supports MIDP push mechanism for automatic application launch for NDEF formatted data
• Flexible design and minimal set of mandatory features
• Allows implementations to support only RFID tags or visual tags or both

For More Information
• JSR 257 Contactless Communication API in Java Community ProcessSM
  http://jcp.org/en/jsr/detail?id=257
• NFC Forum   http://www.nfc-forum.org/home
• Visual tag information on AIM Global
     http://www.aimglobal.org/technologies/barcode/
[1]