https://blog.wongcw.com/2018/10/21/java%e8%af%ad%e8%a8%80%e5%bc%80%e6%ba%90%e5%8d%9a%e5%ae%a2%e7%b3%bb%e7%bb%9f%e4%b8%80%e9%94%ae%e5%ae%89%e8%a3%85-solo/