The book will be using JDK 1.8, which has the support to run Spring 5.0. This version of Java supports @FunctionalInterface and lambda expressions, which are necessary concepts being showcased in this framework. A @FunctionalInterface is an interface with exactly one abstract method that may lead to its instantiation through lambda expressions. Lambda expressions are used to implement anonymous inner classes, avoiding too much bulk in the codes.

Moreover, JDK 1.8 has java.util.stream APIs that can work with collections and NIO 2.0, using stream operations such as filter, map, and reduce. These stream APIs work in sequential and parallel executions. In the area of concurrency, this JDK provides some very essential enhancements on ConcurrentHashMap for its forEach, forEachEntry, forEachKey, forEachValue, compute, merge, reduce, and search methods. Also some changes were done on the object creation of CompletableFuture and Executors.