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Fast, reliable and easy UDP messaging for Java. Designed for games.

JFastNet is tolerant towards packet loss and when used in the right way it can provide your players with a smooth network gaming experience even in bad network conditions.

The API of this library is subject to change.


The dependency for your POM:


Example code

The following code shows the important parts of a server-client communication:

Server server = new Server(new Config().setBindPort(15150));
Client client = new Client(new Config().setPort(15150));


server.send(new PrintMessage("Hello Client!"));
client.send(new PrintMessage("Hello Server!"));

Click to see full sample code of


  • More documentation


The documentation is still a work-in-progress.

The most important classes to look for in the beginning are the Config and the Message class. The JavaDoc there should provide you with the basic configuration possibilities of the library.

Reliable sending

There are currently two ways you can use to send a message in a reliable way. Sending the message unreliably is of course also an option.

  1. Acknowledge packet
  2. Sequence number

Acknowledge packet

The receiver of a message with reliable mode set to ACK_PACKET will send an acknowledge packet to the other end upon receipt of the message. As long as the sender of the prior mentioned message doesn't receive an acknowledge packet it will keep resending the message.

Attribute Value
Reliable yes
Ordered no

Sequence number

The receiver of a message with reliable mode set to SEQUENCE_NUMBER will do nothing as long as the messages arrive in the expected order. But if a message with an id greater than expected is received, the receiver will stop processing the messages and send a RequestSeqIdsMessage to the other end. Processing will not continue until all required messages are received.

Attribute Value
Reliable yes
Ordered yes

It's usually advisable to use sequence numbers, as there will be less overhead and also the ordered delivery is guaranteed.


Use maven to build JFastNet:

mvn clean install


Kryo is the default serialiser used in JFastNet and is a pleasure to work with! Thanks very much for this awesome library!

Project Lombok also deserves a mention, as it makes working with Java much more comfortable and the code looks cleaner. Check it out if you don't have already.


Post issues to the issues page or contact me via email at for other inquiries.