Java Books
Joshua Bloch Effective Java (2001, 2008, 2017)
A Java classic and must read. I of course read all 3 editions.
Joshua Bloch & Neil Gafter Java Puzzlers (2005)
Another classic book by Joshua Bloch, entertaining, enlightening and brain challenging.
Brian Goetz Java Concurrency in Practice (2006)
The classical work on programming low level concurrency on Java using the java.util.concurrent
constructions introduced in Java 1.5.
Li Gong, Gary Ellison og Mary Dageforde Inside Java 2 Platform Security, 2.ed (2003)
Everything about Java security polices, Java Cryptography Architecture (JCA), Java Cryptography Extension (JCE) and Java Authentication and Authorization Service (JAAS)
Stuart Dabbs Halloway Component Development for the Java Platform (2002)
A now old, but very thorough and detailed walk through of the classic Java classloader mechanism, Java serialization and JNI.