General

Code complete 2

Code complete is another book that is extremely valuable and is probably one of the classics in the field. This book is a must read for any developer that wants to improve on their craft. It offers a lot of advice on writing more robust, maintainable, readable, better architected and overall more effective and efficient code. It is one of the best books on programming that exist.

Devflection score: ⭐⭐⭐⭐⭐

The Pragmatic programmer: From Journeyman to Master

Pragmatic programmer is a great book full of insightful tips on how to be a better craftsman. It does not deal with code as much, but the advice it gives is also useful outside of programming. You can find lessons to apply to other professions, or even your life.
Although it does not demonstrate everything concretely with code, a developer eager to learn and improve will still find plenty of great knowledge and good practices to include in his profession.

Devflection score: ⭐⭐⭐⭐ ★

Java

Effective Java 2nd & 3rd edition

Effective Java is a must read for every developer working with Java that cares about the code he is producing. It is organized into self-contained items, which are short statements about what to do or what to avoid. The items are usually a couple of pages long, so the book lends itself well to being a reference while working. You can skim the index, find the item that is applicable and refresh your knowledge in the area.
I particularly like the book, because it backs all the statements with both theory and concrete examples, so you can really understand the reasoning behind the advice given in the item and therefore do not have to follow the advice blindly.
There is not a big difference in the 2nd and 3rd edition so read whatever you have handy, the major thing is that the 3rd edition includes some items that contain Java 8 features.
Still, to be as current as possible I recommend buying the third edition, although I only found the 2nd edition on amazon to link it to.

Devflection score: ⭐⭐⭐⭐⭐

Spring in action

Spring in Action is a great book to help you understand how Spring works and how the different parts are connected and what they are used for. It has a nice way of starting with a big picture view, before diving into the details of a specific part.
If you currently are working with Spring or have a desire to do so, this book will help with understanding some of the “magic” that is happening when you are using Spring.
At the moment I have read the 3rd edition, which is a bit dated, but I still liked it because it’s explaining both the xml configuration and the annotation driven configuration of Spring, which is valuable if you ever encounter an older Spring project, where everything is configured via xmls as opposed to annotations which are used in newer projects. I definitely have the newer editions on my reading list.

Devflection score if you will work with Spring: ⭐⭐⭐⭐⭐
Devflection score if you will never use Spring: ⭐ ★ ★ ★ ★

Other

Algorithms to live by: The computer science of human decision

A really fun book about different practical applications of algorithm solutions. It is not connected directly to developing software, but you might recognize some algorithms that are mentioned in this book.
It is a great book that shows uses of famous CS algorithms in real life situations.
If you are passionate about truly making the optimal decision every time it is a must read ;)

Devflection score: ⭐⭐⭐⭐ ★