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[[Category:Code Examples]][[Category:Java ME]][[Category:Near Field Communication (NFC)]]
Example of NFC LLCP communication in [[Nokia]] 6212 classic. User can exchange messages with other phones by touching them. By default [[MIDlet]] is in reading state and when user wants to write something [[MIDlet]] goes to writing state.

''Note that LLCPConnection class used in this example is proprietary implementation for [[Nokia]] 6212 classic so this example might not work in any other phone.''

<code java>
package com.nokia.nfc.sample.app;

import java.io.IOException;

import javax.microedition.io.Connector;
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.lcdui.TextBox;
import javax.microedition.lcdui.TextField;
import javax.microedition.midlet.MIDlet;
import javax.microedition.midlet.MIDletStateChangeException;

import com.nokia.nfc.llcp.LLCPConnection;
import com.nokia.nfc.llcp.LLCPConnectionListener;
import com.nokia.nfc.llcp.LLCPLinkListener;
import com.nokia.nfc.llcp.LLCPManager;

public class LLCPChat extends MIDlet implements CommandListener, LLCPConnectionListener, LLCPLinkListener {

	/**
	 * LLCP manager 
	 */
	private LLCPManager llcpManager		= null;

	/**
	 * LLCP connections
	 * 
	 * @note
	 * Both inbound (connection received from connectionOpened() method) and
	 * outbound connection (created after linkEstablished() method call)
	 * needs to be created.
	 */ 
	private LLCPConnection inbound;
	private LLCPConnection outbound;

	/**
	 * Connection parameters
	 * 
	 * @note
	 * Connection URI e to open a Type 2 connection that uses service identifier
	 * (SID) 7. Note that PID mentioned in the SDK javadocs is not valid, use SID
	 * instead
	 */
	private static final byte SID		= 7;
	private static final byte TYPE		= LLCPConnection.TYPE_2;

	/**
	 * Connection data buffers
	 */
	private byte[] sendBuffer		= null;
	private byte[] receiveBuffer		= null;

	/**
	 * UI elements
	 */
	private Display display			= null;
	private Form form			= null;
	private TextBox textTextBox		= null;

	/**
	 * Commands
	 */
	private Command writeCmd		= null;
	private Command cancelCmd		= null;
	private Command exitCmd			= null;

	/**
	 * "State machine" - is the MIDlet in reading or writing state
	 */
	boolean reading = true;

	/*
	 * 
	 */
	public LLCPChat() {
		System.out.println("\n\n LLCPChat started");

		/**
		 *  Initialize UI
		 */
		display		= Display.getDisplay(this);

		form		= new Form("LLCPChat");

		writeCmd	= new Command("Write", Command.ITEM, 1);
		cancelCmd	= new Command("Cancel", Command.CANCEL, 1);
		exitCmd		= new Command("Exit", Command.EXIT, 1);

		form.addCommand(writeCmd);
		form.addCommand(exitCmd);
		form.setCommandListener(this);

		display.setCurrent(form);

	}

	/**
	 * This is called when MIDlet is closing or entering to paused state
	 */
	private void close() {
		System.out.println("close");

		llcpManager.stopListening(TYPE, SID, this);
		llcpManager.removeLinkListener(this);

		inbound = closeConn(inbound);
		outbound = closeConn(outbound);

	}

	/**
	 * This is called by both inbound and outbound connection handlers to
	 * close existing connections.
	 * 
	 * @param conn
	 * @return null when connection is closed 
	 */
	private final LLCPConnection closeConn(LLCPConnection conn) {
		System.out.println("closeConn");

		if (conn != null) {
			try {
				conn.close();
			} catch (IOException e) {
				System.out.println("Error closing connection : " + e.getMessage());
			}
		}
		return null;
	}

	/*
	 * (non-Javadoc)
	 * @see javax.microedition.lcdui.CommandListener#commandAction(javax.microedition.lcdui.Command, javax.microedition.lcdui.Displayable)
	 */	
	public void commandAction(Command c, Displayable d) {
		System.out.println("commandAction");

		if (c == writeCmd && d == form) {
			displayWritingTextBox();
		} else if (c == writeCmd && d == textTextBox) {
			write();
		} else if (c == cancelCmd) {
			read();
		} else if (c == exitCmd) {
			notifyDestroyed();
		}
	}

	/*
	 * (non-Javadoc)
	 * @see com.nokia.nfc.llcp.LLCPConnectionListener#connectionOpened(com.nokia.nfc.llcp.LLCPConnection)
	 */
	public void connectionOpened(LLCPConnection conn) {
		System.out.println("connectionOpened");
		if (inbound == null) {
			inbound = conn;
			handleIn();
		} else {
			closeConn(conn);
		}
	}

	/**
	 * This is called to display the text writing box 
	 */
	private void displayWritingTextBox() {
		System.out.println("writeTb");

		textTextBox = new TextBox("Text to write", null, 255, TextField.ANY);
		textTextBox.addCommand(writeCmd);
		textTextBox.addCommand(cancelCmd);
		textTextBox.setCommandListener(this);

		display.setCurrent(textTextBox);

	}

	/*
	 * (non-Javadoc)
	 * @see javax.microedition.midlet.MIDlet#destroyApp(boolean)
	 */
	protected void destroyApp(boolean unconditional) throws MIDletStateChangeException {
		System.out.println("destroyApp");
		close();
	}

	/**
	 * Inbound connection handler
	 */
	private final void handleIn() {
		System.out.println("handleIn");

		new Thread() {
			public void run() {

				System.out.println("handleIn begin");

				try {
					if(reading) {
						sendData(inbound, "-1".getBytes());
						byte[] data  = receiveData(inbound);
						handleReceivedData(data);
					} else {
						sendData(inbound, sendBuffer);
						byte[] data = receiveData(inbound);
						if(new String(data).equals("-1")) handleReceivedData(data);
					}
				} catch (Exception e) {
					System.out.println("Error handling incoming connection : " + e.getMessage());
				}

				System.out.println("handleIn end");

			}
		}.start();
	}

	/**
	 * 
	 * @param uid
	 */
	private final void handleOut(final String uid) {
		System.out.println("handleOut");

		new Thread() {
			public void run() {

				System.out.println("handleOut begin");

				try {
					outbound = (LLCPConnection) Connector.open("nfc:llcp;type=" + TYPE + ";sid=" + SID + ";uid=" + uid);
					System.out.println("Opened outgoing connection");

					if(reading) {
						sendData(outbound, "-1".getBytes());
						byte[] data  = receiveData(outbound);
						handleReceivedData(data);
					} else {
						sendData(outbound, sendBuffer);
						byte[] data = receiveData(outbound);
						if(new String(data).equals("-1")) handleReceivedData(data);
					}

				} catch (IOException e) {
					System.out.println("Error handling outgoing connection : " + e.getMessage());
				}

				System.out.println("handleOut end");

			}
		}.start();
	}

	/**
	 * 
	 * @param data
	 */
	private synchronized void handleReceivedData(byte[] data) {
		System.out.println("handleReceivedData");

		/*
		 * Handle only first arrived respose from either inbound or 
		 * outbound connection handlers
		 */
		if(receiveBuffer == null) {
			receiveBuffer = data;
		} else return;

		if(reading) {
			if(!new String(receiveBuffer).equals("-1")) {
				form.append(">> " + new String(receiveBuffer) + "\n");
			}
		} else {
			if(sendBuffer != null) {
				form.append("<< " + new String(sendBuffer) + "\n");
				read();
			}
		}
	}

	/*
	 * (non-Javadoc)
	 * @see com.nokia.nfc.llcp.LLCPLinkListener#linkEstablished(java.lang.String)
	 */
	public void linkEstablished(String uid) {
		System.out.println("linkEstablished");  	

		receiveBuffer = null;
		handleOut(uid);

	}

	/*
	 * (non-Javadoc)
	 * @see com.nokia.nfc.llcp.LLCPLinkListener#linkLost()
	 */
	public void linkLost() {
		System.out.println("linkLost");

		outbound = closeConn(outbound);
		inbound = closeConn(inbound);

	}

	/**
	 * This is called when MIDlet has started or resumed from paused state
	 */
	private void open() {
		System.out.println("open");

		try {
			llcpManager = LLCPManager.getInstance();
		} catch (Exception e) {
			System.out.println("Failed to get LLCPManager instance : " + e.getMessage());
			return;
		}

		llcpManager.addLinkListener(this);
		llcpManager.startListening(TYPE, SID, this);

	}

	/*
	 * (non-Javadoc)
	 * @see javax.microedition.midlet.MIDlet#pauseApp()
	 */
	protected void pauseApp() {
		System.out.println("pauseApp");

		close();
	}

	/**
	 * 
	 */
	private void read() {
		System.out.println("read");

		sendBuffer = null;
		receiveBuffer = null;

		reading = true;
		display.setCurrent(form);

	}

	/**
	 * 
	 * @param conn
	 * @return
	 * @throws IOException
	 */
	private final byte[] receiveData(LLCPConnection conn) throws IOException {
		System.out.println("receiveData");

		byte[] recv = conn.receive();
		System.out.println("Received " + new String(recv));
		return recv;

	}

	/**
	 * 
	 * @param conn
	 * @param data
	 * @throws IOException
	 */
	private final void sendData(LLCPConnection conn, byte[] data) throws IOException {
		System.out.println("sendData");

		if(data == null) data = "\n".getBytes();

		conn.send(data);
		System.out.println("Sent " + new String(data));
	}

	/*
	 * (non-Javadoc)
	 * @see javax.microedition.midlet.MIDlet#startApp()
	 */
	protected void startApp() throws MIDletStateChangeException {
		System.out.println("startApp");

		open();
	}

	/**
	 * 
	 */
	private void write() {
		System.out.println("write");

		reading = false;
		sendBuffer = textTextBox.getString().getBytes();

		// Show alert
		Alert a = new Alert("Writing", "Touch to write", null, AlertType.INFO);
		a.addCommand(cancelCmd);
		a.setTimeout(Alert.FOREVER);
		a.setCommandListener(this);
		display.setCurrent(a);

	}
}
</code>