Some good blog posts included

Dubbo one article is enough: from entry to actual combat: https://segmentfault.com/a/1190000019896723

Java multithreading related: https://www.cnblogs.com/dolphin0520/category/1426288.html
source code analysis of thread pool: https://www.jianshu.com/p/a977ab6704d7

Four types of references in java: https://blog.csdn.net/u011101295/article/details/105712208
https://www.zhihu.com/question/37401125