A simple and educational TCP client-server project in Java, built with the standard java.net library.
It demonstrates real-time text message exchange where the server echoes back exactly what the client sends, ensuring low latency, message integrity, and clean session termination.

• Server accepts client connections (one at a time, sequentially).
• UTF-8 text communication with line termination (\n).
• Special command QUIT closes the session safely.
• Client measures and prints round-trip time (RTT) for each message.
• Clean, well-structured, and documented code for learning and testing.
• Encrypted communication using Java's built-in TLS/SSL support (javax.net.ssl)
• Server identity validation through a self-signed certificate
• Token-based authentication before message exchange

• Java 21 (or any modern JDK version)
• IntelliJ IDEA or any preferred IDE
• Linux, macOS, or Windows

src/
└── main/java/br/undf/javatcpserver/
├── EchoServer.java
└── EchoClient.java
certs/

From the project root:

javac -encoding UTF-8 -d out $(find src -name "*.java")

Start the server:

java -cp out br.undf.javatcpserver.EchoServer 5000

Start the client:

java -cp out br.undf.javatcpserver.EchoClient 127.0.0.1 5000

Server terminal:

[server] starting on port 5000 ...
[server] client /127.0.0.1:60678 connected
[server] client /127.0.0.1:60678 disconnected

Client terminal:

[client] connecting to 127.0.0.1:5000 ...
[client] type messages. 'QUIT' to exit.
[client] > hello
[server] > hello  (RTT=1ms)
[client] > QUIT
[server] > BYE  (RTT=1ms)

Each user must generate their own keystore and truststore, as certificates are private and not shared in the repository.

Run these commands from the project root (Linux/macOS terminal or Windows PowerShell):

keytool -genkeypair -alias serverkey -keyalg RSA -keysize 2048 \
-keystore certs/server.keystore -storepass senha123 -validity 365

keytool -export -alias serverkey -keystore certs/server.keystore \
-file certs/server.cer -storepass senha123

keytool -import -alias serverkey -file certs/server.cer \
-keystore certs/client.truststore -storepass senha123 -noprompt

The files will be generated inside the certs/ folder:

certs/
├── server.keystore
├── server.cer
└── client.truststore