Write an wifi client server Android application

need a very simple client server wifi app . its a simple text string transfer via wifi concept so dont bid high unnecessarily . try to understand following example : now suppose server app is installed on one phone and client app installed on 4 phones . all the phones are connect to same wifi network (not hotspot) . now client apps on these 4 phones should be connected to the server app automatically whenever server app is on . now server app has 4 text fields , to input text . and client app has 4 text fields to display text . so when the text is added in the server app , the text fields of all other phones having client app should get this text displayed , if client app is not kept opened on the 4 phones , then text update should come as notification . both server and client app should run in background if are on , and if they are running in background it should show in background .