The book will teach you how to create scalable streaming messaging systems using Pulsar. You'll start with a quick introduction to enterprise messaging and discover the unique benefits of Pulsar. By following clear descriptions and performing case studies, you will use the Pulsar Functions framework to develop a microservices-based application. The book "Apache Pulsar in Action" is intended mainly for Java developers interested in streaming data technology, or for microservice developers who are looking for an alternative framework for generating events. DevOps groups interested in deploying and operating Pulsar in their organizations will also find this book useful. One of the main criticisms of Apache Pulsar is the general lack of documentation and blog posts, available on the Internet, and, while no doubt expected to change in the near future, i hope the book will help fill that gap in the interim and benefit everyone, who wants to know more about streaming in general and Apache Pulsar in particular. Prior knowledge of the Apache Pulsar platform is not required.