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流水号格式为yyyyMMddXXXX，规定每天只能到9999，代码如下：

import java.text.DecimalFormat;import java.text.SimpleDateFormat;import java.util.Date; public class PrimaryGenerater {     private static final String SERIAL_NUMBER = "XXXX"; // 流水号格式    private static PrimaryGenerater primaryGenerater = null;     private PrimaryGenerater() {    }     /**     * 取得PrimaryGenerater的单例实现     *      * @return     */    public static PrimaryGenerater getInstance() {        if (primaryGenerater == null) {            synchronized (PrimaryGenerater.class) {                if (primaryGenerater == null) {                    primaryGenerater = new PrimaryGenerater();                }            }        }        return primaryGenerater;    }     /**     * 生成下一个编号     */    public synchronized String generaterNextNumber(String sno) {        String id = null;        Date date = new Date();        SimpleDateFormat formatter = new SimpleDateFormat("yyyyMMdd");        if (sno == null) {            id = formatter.format(date) + "0001";        } else {            int count = SERIAL_NUMBER.length();            StringBuilder sb = new StringBuilder();            for (int i = 0; i < count; i++) {                sb.append("0");            }            DecimalFormat df = new DecimalFormat("0000");            id = formatter.format(date)                    + df.format(1 + Integer.parseInt(sno.substring(8, 12)));        }        return id;    }}

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