it would take me weeks to find my way around it.
You really want to build an XMPP server from scratch? I appreciate the idea and I don't want to get you demotivated, but I estimate it will take you months and I think it's a lot harder than you might think.
It's not only about sending messages from A to B and "something to route them".
You need to understand the concepts around java.nio (working with ServerSocketChannel or AsynchronousServerSocketChannel) which isn't trivial (don't use ServerSocket!).
Then you need to understand TLS and Java's SSLEngine, which isn't trivial either.(You can also use a NIO framework, but I don't know if it's easier, because you would have to learn the framework as well).
Then you have to understand SASL (javax.security.sasl) to implement authentication.
If you are familiar with all those things, it's very valuable knowledge, but most developers aren't.
Then you have to read and re-read and re-read the XMPP specifications to get things right and implement all of the mandatory core features, which are required before sending the first message (Connection management, TLS negotitation, SASL authentication, Resource Binding, Stream features, error handling, routing, etc.).
These are really only the basic requirements for a minimal XMPP server... as you can see, a lot to understand and a lot to implement.
And don't use Tinder, it won't help you much for the tasks above and even when you're done with them, I wouldn't recommend it.