Read NFC Tag UID

ReadNfcUIDActivity.java

// Needed in AndroidManifest:
<!-- Permission for using NFC hardware -->
<uses-permission android:name="android.permission.NFC"/>
<!-- Forcing device to have NFC hardware -->
<uses-feature android:name="android.hardware.nfc" android:required="true"/>
<!-- Registering app for receiving NFC's TAG_DISCOVERED intent -->
<intent-filter>
  <action android:name="android.nfc.action.TAG_DISCOVERED"/>
  <category android:name="android.intent.category.DEFAULT"/>
</intent-filter>




// handling ACTION_TAG_DISCOVERED action from intent:
@Override
protected void onResume() {
	super.onResume();
	if (getIntent().getAction().equals(NfcAdapter.ACTION_TAG_DISCOVERED)) {
		((TextView)findViewById(R.id.text)).setText(
				"NFC Tag\n" + 
				this.ByteArrayToHexString(getIntent().getByteArrayExtra(NfcAdapter.EXTRA_ID)));
	}
}

// Converting byte[] to hex string:
private String ByteArrayToHexString(byte [] inarray) {
    int i, j, in;
    String [] hex = {"0","1","2","3","4","5","6","7","8","9","A","B","C","D","E","F"};
    String out= "";

    for(j = 0 ; j < inarray.length ; ++j) 
        {
        in = (int) inarray[j] & 0xff;
        i = (in >> 4) & 0x0f;
        out += hex[i];
        i = in & 0x0f;
        out += hex[i];
        }
    return out;
}

ReadNfcUIDOnlyInsideActivity.java

package es.luixal.ragbag;

import android.app.Activity;
import android.app.PendingIntent;
import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.content.IntentFilter;
import android.nfc.NfcAdapter;
import android.nfc.tech.IsoDep;
import android.nfc.tech.MifareClassic;
import android.nfc.tech.MifareUltralight;
import android.nfc.tech.Ndef;
import android.nfc.tech.NfcA;
import android.nfc.tech.NfcB;
import android.nfc.tech.NfcF;
import android.nfc.tech.NfcV;
import android.os.Bundle;
import android.util.Log;
import android.view.Menu;
import android.widget.TextView;

public class MainActivity extends Activity {
  
	// list of NFC technologies detected:
	private final String[][] techList = new String[][] {
			new String[] {
				NfcA.class.getName(),
	            NfcB.class.getName(),
	            NfcF.class.getName(),
	            NfcV.class.getName(),
	            IsoDep.class.getName(),
	            MifareClassic.class.getName(),
	            MifareUltralight.class.getName(), Ndef.class.getName()
			}
	};
	
	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.main_activity);
	}

	@Override
	public boolean onCreateOptionsMenu(Menu menu) {
		// Inflate the menu; this adds items to the action bar if it is present.
		getMenuInflater().inflate(R.menu.main_activity, menu);
		return true;
	}
	
	@Override
	protected void onResume() {
		super.onResume();
		// creating pending intent:
		PendingIntent pendingIntent = PendingIntent.getActivity(this, 0, new Intent(this, getClass()).addFlags(Intent.FLAG_ACTIVITY_SINGLE_TOP), 0);
		// creating intent receiver for NFC events:
		IntentFilter filter = new IntentFilter();
		filter.addAction(NfcAdapter.ACTION_TAG_DISCOVERED);
		filter.addAction(NfcAdapter.ACTION_NDEF_DISCOVERED);
		filter.addAction(NfcAdapter.ACTION_TECH_DISCOVERED);
		// enabling foreground dispatch for getting intent from NFC event:
		NfcAdapter nfcAdapter = NfcAdapter.getDefaultAdapter(this);
		nfcAdapter.enableForegroundDispatch(this, pendingIntent, new IntentFilter[]{filter}, this.techList);
	}
	
	@Override
	protected void onPause() {
		super.onPause();
		// disabling foreground dispatch:
		NfcAdapter nfcAdapter = NfcAdapter.getDefaultAdapter(this);
		nfcAdapter.disableForegroundDispatch(this);
	}
	
	@Override
	protected void onNewIntent(Intent intent) {
		if (intent.getAction().equals(NfcAdapter.ACTION_TAG_DISCOVERED)) {
			((TextView)findViewById(R.id.text)).setText(
					"NFC Tag\n" + 
					ByteArrayToHexString(intent.getByteArrayExtra(NfcAdapter.EXTRA_ID)));
		}
	}
	
	private String ByteArrayToHexString(byte [] inarray) {
	    int i, j, in;
	    String [] hex = {"0","1","2","3","4","5","6","7","8","9","A","B","C","D","E","F"};
	    String out= "";
	
	    for(j = 0 ; j < inarray.length ; ++j) 
	        {
	        in = (int) inarray[j] & 0xff;
	        i = (in >> 4) & 0x0f;
	        out += hex[i];
	        i = in & 0x0f;
	        out += hex[i];
	        }
	    return out;
	}

}

Thank you!