Spring in Action

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You may also notice that all three dependencies have the word starter in their artifact ID. Spring Boot starter dependencies are special in that they typically don’t have any library code themselves, but instead transitively pull in other libraries. These starter dependencies offer three primary benefits: Finally, the build specification ends with the Spring Boot plugin. This plugin performs a few important functions: Chapter 12 takes a look at writing reactive data persistence with Spring Data to read and write data to Cassandra and Mongo databases. Your build file will be significantly smaller and easier to manage because you won’t need to declare a dependency on every library you might need. Craig Walls is an engineer at VMware, a member of the Spring engineering team, a popular author, and a frequent conference speaker. The best resource for modern Spring development.

Any non-trivial application is composed of many components, each responsible for its own piece of the overall application functionality, coordinating with the other application elements to get the job done. When the application is run, those components somehow need to be created and introduced to each other.

about the authors

Although the Greek philosopher Heraclitus wasn’t well known as a software developer, he seemed to have a good handle on the subject. He has been quoted as saying, The only constant is change. That statement captures a foundational truth of software development. Part 1 of this book will get you started writing a Spring application, learning the foundations of Spring along the way. Spring Framework makes life easier for Java developers. New features in Spring 5 bring its productivity-focused approach to microservices, reactive development, and other modern application designs. With Spring Boot now fully integrated, you can start even complex projects with minimal configuration code. And the upgraded WebFlux framework supports reactive apps right out of the box! Spring Boot enhances Spring development so much that it’s hard to imagine developing Spring applications without it. For that reason, this book treats Spring and Spring Boot as if they were one and the same. We’ll use Spring Boot as much as possible, and explicit configuration only when necessary. And, because Spring XML configuration is the old-school way of working with Spring, we’ll focus primarily on Spring’s Java-based configuration.

You may recognize this as a typical Maven or Gradle project structure, where application source code is placed under src/main/java, test code is placed under src/test/java, and non-Java resources are placed under src/main/resources. Within that project structure, you’ll want to take note of these items: As for the dependencies themselves, you can either expand the various sections and seek out the desired dependencies manually, or search for them in the search box at the top of the Available list. For the Taco Cloud application, you’ll start with the dependencies shown in figure 1.4. Although all of the projects in the Spring ecosystem provide excellent documentation, this book does something that none of the reference documents do: provide a hands-on, project-driven guide to bringing the elements of Spring together to build a real application. Who should read this book mvnw and mvnw.cmd—These are Maven wrapper scripts. You can use these scripts to build your project even if you don’t have Maven installed on your machine. It provides a Maven goal that enables you to run the application using Maven. You’ll try out this goal in section 1.3.4.As always, there’d be absolutely no point in writing this book if it weren’t for the amazing work done by the members of the Spring engineering team. I’m amazed at what you’ve created and how we continue to change how software is developed. The act of wiring beans together is based on a pattern known as dependency injection (DI). Rather than have components create and maintain the lifecycle of other beans that they depend on, a dependency-injected application relies on a separate entity (the container) to create and maintain all components and inject those into the beans that need them. This is done typically through constructor arguments or property accessor methods.

You’re able to think of your dependencies in terms of what capabilities they provide, rather than in terms of library names. If you’re developing a web application, you’ll add the web starter dependency rather than a laundry list of individual libraries that enable you to write a web application. After ten years, this is still the clearest and most comprehensive introduction to the core concepts of the Spring platform. It ensures that all dependency libraries are included within the executable JAR file and available on the runtime classpath. Next, take note of the element and, more specifically, its child. This specifies that your project has spring-boot-starter-parent as its parent POM. Among other things, this parent POM provides dependency management for several libraries commonly used in Spring projects. For those libraries covered by the parent POM, you won’t have to specify a version, as it’s inherited from the parent. The version, 2.0.4.RELEASE, indicates that you’re using Spring Boot 2.0.4 and, thus, will inherit dependency management as defined by that version of Spring Boot.Finally, to my beautiful wife Raymie, the love of my life, my sweetest dream, and my inspiration: Thank you for your encouragement and for putting up with another book project. And to my sweet and wonderful girls, Maisy and Madi: I am so proud of you and of the amazing young ladies you are becoming. I love all of you more than you can imagine or I can possible express. About this book Chapter 15 introduces the circuit breaker pattern with Hystrix, enabling microservices that are resilient in the face of failure. Part 4 breaks down the monolithic application model, introducing you to Spring Cloud and microservice development: If you’re not a Spring Tool Suite user, that’s fine; we can still be friends. Hop over to the appendix and substitute the Initializr option that suits you best for the instructions in the following sections. But know that throughout this book, I may occasionally reference features specific to Spring Tool Suite, such as the Spring Boot Dashboard. If you’re not using Spring Tool Suite, you’ll need to adapt those instructions to fit your IDE.

But enough of this chitchat, yakety-yak, and flimflam. This book’s title includes the phrase in action, so let’s get moving, and you can start writing your first application with Spring. 1.2. Initializing a Spring application The definitive guide for developers wanting to build reliable, fault-tolerant, and scalable cloud-native applications using Spring.What’s more, as developers look to break down their monolithic applications into discrete microservices, Spring Cloud provides facilities that make it easy to configure and discover microservices, as well as fortify them so they’re more resilient to failure. Chapter 14 shows how to centralize application configuration in a configuration server that shares configuration across multiple microservices.