转发： ThreadLocal避免内存泄露

【ThreadLocal面试六连问，你能Hold住吗？ - 今日头条】https://m.toutiaocdn.com/group/6764905475558343180/?app=news_article&timestamp=1575189652&req_id=20191201164052010014041157332850E2&group_id=6764905475558343180&tt_from=copy_link&utm_source=copy_link&utm_medium=toutiao_ios&utm_campaign=client_share