1 Spring in the real world

Spring is presented as a widely used application framework in the Java/JVM ecosystem that helps developers build many kinds of applications more efficiently. The main idea is that frameworks provide reusable software capabilities for common needs—such as logging, security, database access, communication between applications, transactions, caching, and testing—so developers can focus more on business logic instead of repeatedly writing “plumbing” code from scratch. The text emphasizes that frameworks are not the same as libraries: libraries are called by application code for specific tasks, while frameworks provide a broader structure and often control parts of the application’s execution.

The Spring ecosystem is described as much larger than a single framework. Its foundation is Spring Core, which includes the Spring context, inversion of control, aspect-oriented capabilities, and configuration support. Through inversion of control, Spring manages objects and can call or intercept application code based on configuration. Around this core, Spring offers tools for web applications, persistence, testing, security, cloud development, batch processing, and convention-based application setup through projects such as Spring Data and Spring Boot. The book focuses especially on the foundational parts needed to begin building real-world Spring applications.

The text explains that Spring is most commonly used for backend applications, where it helps manage data, expose services, communicate with other systems, secure functionality, and integrate with databases and message-based systems. It can also be useful in automation testing applications and even desktop applications when object management, persistence, communication, or caching features are needed. At the same time, the text warns that frameworks should not be used blindly: they may be inappropriate when an application must remain very small, when strict security rules require only custom code, when excessive customization would outweigh the benefits, or when replacing an existing working solution provides no real improvement.

David ordered a wardrobe from the UAssemble store. But the store (framework) doesn’t deliver to David (the programmer) just the components (software capabilities) he needs to build his new wardrobe (the app). The store ships him all the possible parts he might need to build the wardrobe. It’s David’s (the programmer’s) choice on which components (software capabilities) are right and how to assemble them to get the right result (the application).

The user’s perspective is like viewing an iceberg. Users mainly observe the results of the business logic code, but this is only a small part of what builds the app’s complete functionality. Like an iceberg that is mostly underwater and hidden from view, we don't see most of the code in an enterprise app because it's provided by dependencies.

You can imagine the Spring framework as a solar system with the Spring Core in the center. The software capabilities are planets around Spring Core kept close to it by its gravitational field.

Inversion of control. Instead of executing its own code, which makes use of several other dependencies, in an IoC scenario, the app execution is controlled by the dependency. The Spring framework controls an app during its execution. Therefore, Spring implements an IoC scenario of execution.

A backend app interacts in several ways with other apps and uses databases to manage data. Usually, a backend app is complex and may require the use of various technologies. Frameworks simplify the implementation by providing tools you can use to implement the backend solution faster.

The possibilities of using Spring in a backend application are endless, from exposing functionalities that other applications can call to managing the database access, and from securing the application to managing integration through third-party message brokers.

The team deploys the testing app in a test environment. A continuous integration tool like Jenkins executes the app regularly and sends feedback to the team. This way, the team is always aware of the system’s status, and they know if they break something during development.

A testing app might need to connect to databases or communicate with other systems or the tested system. The developers can use components of the Spring ecosystem to simplify the implementations of these functionalities.

• An application framework provides common software functionality and a structure for building applications more efficiently and reliably.
• Frameworks like Spring also offer access to large communities, making it easier to find solutions, guidance, and best practices.
• When choosing a framework, always evaluate its purpose, alternatives, maturity, and community adoption.
• Spring is more than a single framework—it is an ecosystem of projects. In this book, we’ll mainly use Spring Core, Spring Data, and Spring Boot.
• Although Spring is commonly associated with backend systems, it can also be used for desktop applications, testing tools, and other kinds of software.

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