The mission of this book is to introduce developers to application monitoring and performance tuning to create highly performant applications. The book starts with the basic details of Spring Framework, including various Spring modules and projects, Spring bean and BeanFactory implementation, and aspect-oriented programming. It also explores Spring Framework as an IoC bean container. We will be discussing Spring MVC, which is a commonly used Spring module for building a user interface in detail with Spring Security authentication part with a stateless API. This book also emphasizes the importance of building optimized Spring applications for interacting with relational databases. Then, we will walk through some of the advanced ways of accessing databases using object-relational mapping (ORM) frameworks, such as Hibernate. The book moves on to the details of new Spring features, such as Spring Boot and reactive programming, with best practices suggestions. An important aspect of the book is its focus on building highly performant applications. The latter part of the book includes details for application monitoring, performance optimization, JVM internals, and garbage collection optimization. Finally, how to build microservices is explained to help you understand the challenges faced in the process and how to monitor its performance.