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;

/**
* JAVA版本的自动生成有规则的订单号(或编号)
* 生成的格式是: 200908010001 前面几位为当前的日期,后面五位为系统自增长类型的编号
* 原理:
* 1.获取当前日期格式化值;
* 2.读取文件,上次编号的值+1最为当前此次编号的值
* (新的一天会重新从1开始编号)
*/

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);
}

/**
* 获得序列号，同时更新持久化存储中的序列
* @param current 当前的日期
* @param start 初始化的序号
* @return 所获得新的序列号
*/
protected abstract int getOrUpdateNumber(Date current, int start);
}

class FileEveryDaySerialNumber extends EveryDaySerialNumber {

/**
* 持久化存储的文件
*/
private File file = null;

/**
* 存储的分隔符
*/
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;
}
}

存储自动编号值的文件如下(文件名: EveryDaySerialNumber.dat)