1、使用RandomAccessFile读文件

2、每次开始读时，先进行一次全读，目的是让seek到结尾。

3、注意编码转换。RandomAccessFile的编码都是ISO_8859_1

@OnOpen
public void onOpen(Session session) {
    onlineCount.incrementAndGet(); // 在线数加1
    log.info("有新连接加入：{}，当前在线人数为：{}", session.getId(), onlineCount.get());

    try {
        RandomAccessFile r = new RandomAccessFile("case.log", "r");
        byte[] bf = new byte[1024*100];
        while (r.read(bf) != -1) {}

        long lastPonit = r.getFilePointer();
        String line = null;
        while (true) {
            r.seek(lastPonit);
            while ((line = r.readLine()) != null) {
                session.getBasicRemote().sendText(new String(line.getBytes(StandardCharsets.ISO_8859_1), "UTF-8") + "\n");
            }
            lastPonit = r.getFilePointer();
        }
    } catch (Exception e) {}


}