Intro

A P2P example made with Java DatagramSocket.

How it works?

It uses a third party to tell peers what their public IP and port is(which is used for send message to the Server), then the peers will try to connect to each other.

And this technique is so called 'hole punching'.

It's not 100% works, depends on the NAT types.

How to build?

Use gradle wrapper to build executable Jar file, then the Peer.jar and the Server.jar will be located at directory ./build/jar

./gradlew build

or if you're using Windows

gradlew.bat build

(Actually, I'm not sure about this, cause my laptop is running Linux :D. I like Linux, BTW.)

Lazy to build?

You can download Jars from here

Run

Peer

Run with command.

java -jar Peer.jar <Server>[:port] [group_id]

The default group_id is default.

Example

If the server address is hello.noip.me.

java -jar Peer.jar hello.noip.me

Server

The default listening port is 5555.

java -jar Server.jar [listening_port]

Example

java -jar Server.jar

How to know is it works?

If other peers join the same group

1.2.3.4:56789 joined

otherwise

1.2.3.4:56789 left

If successfully message from other peers, it'll output something like

1.2.3.4:56789 'Hi! I'm musing_lalande'