There are 2 repositories under java-chat-app topic.
LiveChatServer in java which can supports multi user chat.
Chat in Java with Sockets between a client and a server
A simple Java WebSocket chat application developed with Java, Java JSONB.
A One to One Chat Gui Application Designed in Java.
simple chat app with java sockets
Simple CLI Based Chat
Client side program of chat application made by using Java, Servlet and Java Servlet Pages
Program logic of Chat application by using Java, MySQL and Java Data Base Connection
Sistema de mensajería multi-usuario en red.