使用AtomicInteger实现自增长编号

public class TextUtil {
    public static ConcurrentHashMap<String, AtomicInteger> ID = new ConcurrentHashMap<>();
    private static String timeFlag;
    static {
        //初始值        
        ID.put("num", new AtomicInteger(1));
    }
    /**
     * 生成案件编号，格式：2019082300001
     * @return
     */
    public static String getCaseNo() {
        String now = DateUtil.getDate();
        if (!now.equals(timeFlag)) {
            timeFlag = now;
            ID.get("num").getAndSet(1);
        }
        int nextNum = ID.get("num").getAndIncrement();
        String str = String.format("%05d", nextNum);
        now += str;
        return now;
    }
    public static void main(String[] args) {
        for (int i = 0; i < 20; i++) {
            System.out.println(getCaseNo());
            try {
                Thread.sleep(1000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }
}

public class TextUtil {
    public static ConcurrentHashMap<String, AtomicInteger> ID = new ConcurrentHashMap<>();
    private final static String file = TextUtil.class.getResource("").getPath() + "eventId.ini";
    private static String timeFlag;
    static {
        //初始值
        //程序启动时获取文件内容
        String str = read();
        int num = 1;
        if (StringUtils.isNotBlank(str)) {
            timeFlag = str.substring(0, 8);//最后更新日期，格式：yyyyMMdd
            String numStr = str.substring(8);
            num = Integer.parseInt(numStr);
            num++;
        }
        ID.put("num", new AtomicInteger(num));
    }
    /**
     * 生成编号，格式：2019082300001 
     *
     * @return
     */
    public static String getCaseNo() {
        String now = DateUtil.getDate();
        if (!now.equals(timeFlag)) {
            timeFlag = now;
            ID.get("num").getAndSet(1);
        }
        int nextNum = ID.get("num").getAndIncrement();
        store(nextNum + "");
        String str = String.format("%05d", nextNum);
        now += str;
        store(now);
        return now;
    }
    //存数据
    private static void store(String eventId) {
        //写入相应的文件
        BufferedOutputStream out = null;
        try {
            out = new BufferedOutputStream(new FileOutputStream(file));
            byte[] bytes = eventId.getBytes();
            //写入文件
            out.write(bytes, 0, bytes.length);
            //清缓存
            out.flush();
            out.close();
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            if (out != null) {
                try {
                    //清缓存
                    out.flush();
                    out.close();
                } catch (Exception e) {
                }
            }
        }
    }
    //读数据
    private static String read() {
        String str = "";
        //读取文件(缓存字节流)
        BufferedInputStream in = null;
        try {
            File f = new File(file);
            if (!f.exists()) {
                f.createNewFile();
            }
            in = new BufferedInputStream(new FileInputStream(f));
            //读取数据
            //一次性取多少字节
            byte[] bytes = new byte[32];
            //接受读取的内容(n就代表的相关数据，只不过是数字的形式)
            int n = -1;
            //循环取出数据
            while ((n = in.read(bytes, 0, bytes.length)) != -1) {
                //转换成字符串
                str = new String(bytes, 0, n, "UTF-8");
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            //关闭流
            if (in != null) {
                try {
                    in.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
        return str;
    }
    public static void main(String[] args) {
        for (int i = 0; i < 20; i++) {
            System.out.println(getCaseNo());
            try {
                Thread.sleep(1000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }
}