java中自动生成有规律的编号

java中自动生成有规律的编号,例如例如2015080001,2015080002,而且每个月的第一个编号必须是xxxxxx0001,前面六位是当前年月

实现思路：在本地存储一个文本文件用于记录上一次的编号序数，生成编号时从文件里读出编号序数后加一，并把结果保存回文件中以备下次生成使用。如此处理即可达成需求，具体代码如下（运行环境：jdk8或以上）：

package com.file;

import java.io.BufferedReader;
import java.io.File;
import java.io.FileOutputStream;
import java.io.FileReader;
import java.io.IOException;
import java.time.LocalDate;


public class NoCreater {

public static void main(String[] args) {
System.out.println(next());
}


public static String next() {
File file = getCountFile();
try (BufferedReader fr = new BufferedReader(new FileReader(file))) {
int nextNum = Integer.valueOf(fr.readLine()) + 1;
try (FileOutputStream fos = new FileOutputStream(file)) {
fos.write(String.valueOf(nextNum).getBytes());
}
String next = "";
if (nextNum / 10 < 1) {
next += "000" + nextNum;
} else if (nextNum / 100 < 1) {
next += "00" + nextNum;
} else if (nextNum / 1000 < 1) {
next += "0" + nextNum;
} else {
next += nextNum;
}
int year = LocalDate.now().getYear();
int month = LocalDate.now().getMonthValue();
return year + "" + month + next;
} catch (IOException e) {
e.printStackTrace();
return "生成编号出错";
}
}

private static File getCountFile() {
File file = new File("count.txt");
if (!file.exists()) {
try {
file.createNewFile();
try (FileOutputStream fos = new FileOutputStream(file)) {
fos.write("0".getBytes());
}
} catch (IOException e) {
e.printStackTrace();
return null;
}
}
return file;
}
}

public class main { private static long n = 1; public static void main(string[] args) { system.out.println(test(n)); system.out.println(test(n)); } public static long test(long l) { string str = new simpledateformat("yyyymm") .format(new java.util.date()); long m = long.parselong((str)) * 10000; long ret = m + l; n = l + 1; return ret; } }