Whenever you publish a page, component or another type of item in Tridion, the item is first published, then transported and finally deployed. SDL offers various ways to extend or modify this deployment process. All you need to do is write some custom java code. The most commonly used extension points are deployer modules and storage DAOs. You can find more about this here and here.
In this post I’m not going to explain what these extensions are and what you can do with them. Instead, I will focus on how to develop this type of extension effectively. As always with Java (in my experience at least), the code is easy but the environment is hard. But if you follow these instructions, you will be able to run your customizations locally, make sure they get triggered, and even perform step-through debugging on your code. Pure bliss!