JAVA流水号生成规格，采用同步单例生成，保证永远唯一

流水号格式为yyyyMMddXXXX，规定每天只能到9999，代码如下：

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

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