package com.xmobo.demo;

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.File;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
import java.text.DecimalFormat;
import java.text.SimpleDateFormat;
import java.util.ArrayList;
import java.util.Date;
import java.util.List;
import java.util.concurrent.TimeUnit;

public class Test01 {

	public static void main(String[] args) throws InterruptedException {
		SerialNumber serial = new FileEveryDaySerialNumber(5, "EveryDaySerialNumber.dat");
		while (true) {
			System.out.println(serial.getSerialNumber());
			TimeUnit.SECONDS.sleep(2);
		}
	}
}

abstract class SerialNumber {
	public synchronized String getSerialNumber() {
		return process();
	}

	protected abstract String process();
}

abstract class EveryDaySerialNumber extends SerialNumber {

	protected final static SimpleDateFormat sdf = new SimpleDateFormat("yyyyMMdd");
	protected DecimalFormat df = null;

	public EveryDaySerialNumber(int width) {
		if (width < 1) {
			throw new IllegalArgumentException("Parameter length must be great than 1!");
		}
		char[] chs = new char[width];
		for (int i = 0; i < width; i++) {
			chs[i] = '0';
		}
		df = new DecimalFormat(new String(chs));
	}

	protected String process() {
		Date date = new Date();
		int n = getOrUpdateNumber(date, 1);
		return format(date) + format(n);
	}

	protected String format(Date date) {
		return sdf.format(date);
	}

	protected String format(int num) {
		return df.format(num);
	}

	protected abstract int getOrUpdateNumber(Date current, int start);
}

class FileEveryDaySerialNumber extends EveryDaySerialNumber {

	private File file = null;

	private final static String FIELD_SEPARATOR = ",";

	public FileEveryDaySerialNumber(int width, String filename) {
		super(width);
		file = new File(filename);
	}

	@Override
	protected int getOrUpdateNumber(Date current, int start) {
		String date = format(current);
		int num = start;
		if (file.exists()) {
			List<String> list = FileUtil.readList(file);
			String[] data = list.get(0).split(FIELD_SEPARATOR);
			if (date.equals(data[0])) {
				num = Integer.parseInt(data[1]);
			}
		}
		FileUtil.rewrite(file, date + FIELD_SEPARATOR + (num + 1));
		return num;
	}
}

class FileUtil {
	public static void rewrite(File file, String data) {
		BufferedWriter bw = null;
		try {
			bw = new BufferedWriter(new FileWriter(file));
			bw.write(data);
		} catch (IOException e) {
			e.printStackTrace();
		} finally {
			if (bw != null) {
				try {
					bw.close();
				} catch (IOException e) {
					e.printStackTrace();
				}
			}
		}
	}

	public static List<String> readList(File file) {
		BufferedReader br = null;
		List<String> data = new ArrayList<String>();
		try {
			br = new BufferedReader(new FileReader(file));
			for (String str = null; (str = br.readLine()) != null;) {
				data.add(str);
			}
		} catch (IOException e) {
			e.printStackTrace();
		} finally {
			if (br != null) {
				try {
					br.close();
				} catch (IOException e) {
					e.printStackTrace();
				}
			}
		}
		return data;
	}
}

注意：代码中有个叫EveryDaySerialNumber.dat，可以自行创建这样的文件，然后放到项目的根目录下就可以。此文件主要是用于记录上一次执行程序的节点。