- kafka: https://kafkadoc.beanmr.com/ https://www.gitbook.com/book/ddfeng/apache-kafka-documentation-cn/details
- countdownlatch: http://www.importnew.com/15731.html
- spring boot: https://docs.spring.io/spring-boot/docs/current-SNAPSHOT/reference/htmlsingle/#getting-started-first-application-code
- markdown: https://github.com/adam-p/markdown-here/wiki/Markdown-Cheatsheet