Java以寫文件的形式對學號進行遞增處理

package com.wzxy.chapter_01;

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;

public class Code {
	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);
	        }*/
	        System.out.println(serial.getSerialNumber());
	    }
	}
	 
	 
	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);
	    }
	     
	    /**
	     * 得到序列號，同時更新持久化存儲中的序列
	     * @param current 當前的日期
	     * @param start   初始化的序號
	     * @return 所得到新的序列號
	     */
	    protected abstract int getOrUpdateNumber(Date current, int start);
	}
	 
	 
	class FileEveryDaySerialNumber extends EveryDaySerialNumber {
	 
	    /**
	     * 持久化存儲的文件
	     */    
	    private File file = null;
	     
	    /**
	     * 存儲的分隔符
	     */
	    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;
	    }
	}