android log to file, will create a log file in sdcard root directory.

appendLog.java

public void appendLog(String text) {
		String logFileName = "AppLog.txt";
		SimpleDateFormat sdf = new SimpleDateFormat("MM-dd HH:mm:ss", Locale.getDefault());
		String currentDateandTime = sdf.format(new Date());
		File logFile = new File(Environment.getExternalStorageDirectory()
				+ "/" + logFileName);
		
		if (!logFile.exists()) {
			try {
				logFile.createNewFile();
			} catch (IOException e) {
				e.printStackTrace();
			}
		}
		try {
			BufferedWriter buf = new BufferedWriter(new FileWriter(logFile,
					true));
			buf.append(currentDateandTime + "    " + text);
			buf.newLine();
			buf.close();
		} catch (IOException e) {
			e.printStackTrace();
		}
	}