One of Gradle's special strengths is its ability to let you define your own build vocabulary, rather than imposing its design on you. Domain-specific languages are great tools for turning your build process from mysticism into something that the entire team can understand. The result is that your build and deployment process becomes more reliable and predictable.
This book goes more into depth about how gradle works. The book is quite dated but it focuses mainly on general ideas of gradle so I think it still makes sense to read it. You have to be careful about actual code examples though. It discusses how to extend gradle via plugins, details of basic build lifecycle and dependency management. The dependency management is especially useful because you will need it if you want to use gradle for more serious projects. The book is also very short which I appreciate. Some technical books are repeating the same information over and over which make tedious to read them.
That is a useful book. It isn't deep because of it's shortness, but it gives you an idea about such topics as working with files, writing plugins, making your own dsl, creating rules, managing dependencies. It can be used as a starting point to dive into more details on the topic of interest in the Gradle documention.
A brief, useful guide to how to use gradle more effectively. It didn't answer all of my questions, but it struck a good balance between density, readability, and use as a reference.
Very good book. It goes hand in hand with "Building and Testing with Gradle" from the same publisher. I recommend reading that first and then this. The two books complement each other very well.