生成流水号

import java.text.Format;
import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.HashMap;
import java.util.Map;

/**
*
* @author Phonnie
*
*/
public class SerialNumber {

private static final int MAX_VALUE=9999;
private static final String FORMAT = "yyMMdd";
private static final Format DF= new SimpleDateFormat(FORMAT);
private static final byte[] lock = new byte[0];
private String prefix = null;
private Date date = null;
private int number=1;
private static Map<String, SerialNumber> map = new HashMap<String, SerialNumber>();

private SerialNumber(String prefix,Date date){
this.prefix = prefix;
this.date = date;
}

public static SerialNumber newInstance(String prefix){
Date date = new Date();
return newInstance(prefix,date);
}

public static SerialNumber newInstance(String prefix,Date date){
SerialNumber o = null;
synchronized (lock) {
String key = getKey(prefix, date);
if(map.containsKey(key)){
o = map.get(key);
int number = o.getNumber();
if(number<MAX_VALUE){
o.setNumber(number+1);
}else {
o.setNumber(1);
}

} else {
o = new SerialNumber(prefix,date);
map.put(key, o);
}
}
return o;
}



private static String getKey(String prefix,Date date){
return prefix+format(date);
}

private static String format(Date date){
return DF.format(date);
}

public String toString(){
return prefix+ format(date) + String.format("%04d", number);
}

public void setNumber(int number) {
this.number = number;
}

public int getNumber() {
return number;
}
}