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◎위챗 : speedseoul
https://examples.javacodegeeks.com/android/android-recyclerview-example/
https://doc-04-44-docs.googleusercontent.com/docs/securesc/ha0ro937gcuc7l7deffksulhg5h7mbp1/lqctlaccd2pac1gkur14s616osqpribn/1570968000000/01468509931138053158/*/0BxVa3_wqOp_rbGlRbVBYZjBNOEE?e=download
http://www.tutorialsface.com/2015/08/building-your-own-android-chat-messenger-app-similar-to-whatsapp-using-xmpp-smack-4-1-api-from-scratch-part-2/