正则表达式

 String str = "暑假放假uD83CuDF22后几天学uD83CuDFF1校开始学习物理知识并实验，从uD83CuDFF4中获得了许多知识uD83DuDE00";
        System.out.println(str);
        Pattern emoji = Pattern.compile ("[ud83cudc00-ud83cudfff]|[ud83dudc00-ud83dudfff]|[u2600-u27ff]",Pattern.UNICODE_CASE | Pattern . CASE_INSENSITIVE );
        Matcher emojiMatcher = emoji.matcher(str);
        String s = emojiMatcher.replaceAll("www.baidu.com");
        System.out.println(s);

https://regex101.com/