What Is Spring Boot?

Writing software is like opening a new blank document in your favorite word processor: What do you do first? And how do you handle all the tedious boilerplate code required to create a complex application without forgetting something important or making a configuration error? That’s where application frameworks, which provide the structure for different types of applications, come in. Once your dev team has chosen an application framework, the process of creating the software can really begin in earnest. No, it’s not as simple as a fill-in-the-blanks template, but an application framework’s scaffolding takes care of the prerequisites for projects ranging from a simple microservice or Web app to a traditional client/server application.

For Java developers, one of the most popular application frameworks is Spring, which is incredibly flexible and versatile. You can do just about anything with Spring from creating a simple service to developing a huge business-critical system. And while versatility is Spring’s greatest strength, it’s also Spring’s greatest weakness: It’s often too complex and offers too many choices. That’s where Spring Boot comes in. Spring Boot is an extension of Spring that’s easier to use because it makes many of the choices for you, particularly around dependency management and configurations.

In short: If you’re thinking about using Spring, you probably can—and should—use Spring Boot instead.

What Is Spring Boot for Java?

Spring Boot is an open source Java-based framework for creating Spring-based applications. Spring, which was developed in the early 2000s, rapidly became one of the most popular Java frameworks for enterprise-grade applications. Spring Boot was launched later as an easier-to-use framework that extends all of Spring’s tools and technologies to enable rapid application development.

Java and Spring Framework

For Java developers, Spring has an impressive array of core technologies, including dependency injection to event management, internationalization, data binding, type conversation, and aspect-oriented programming. You name it, it’s in Spring: testing, mocking, data objects, Model-View-Controller web applications, remoting, task scheduling—the list goes on and on. Developers can choose to use some or all of those features—it’s up to the software development team and architects.

The Spring Framework is open source software under the Apache 2.0 license.

The Spring project has many subprojects, focusing on cloud apps, security, publishing and consuming web services, credentials management, data access, event management, and even artificial intelligence. That flexibility can lead to complexity: Spinning up elaborate Spring-based applications could lead development teams down a rabbit warren of options, choices, and configurations—some of which, once manually set up, are difficult to change once you start coding.

Enter Spring Boot.

Spring vs. Spring Boot

• Spring Boot is one of the subprojects under Spring. It’s also open source under the Apache 2.0 license.
• Some developers are surprised to learn that Spring Boot’s codebase is actually larger than the Spring Framework itself. That’s because Spring Boot is an extension of Spring that’s designed to be intelligently self-configuring; the term used is “opinionated.”
• Once you tell Spring Boot what you’re trying to build, it makes choices regarding which modules and third-party libraries to load and provision.
• One important note: When we say “intelligent” here, we don’t mean AI. Spring Boot’s choices are algorithmic.
• The extra weight of the Spring Boot framework itself doesn’t show up in the completed app. In fact, just the opposite, as Spring Boot almost always chooses only what is needed.
• In other words, while Spring Boot is opinionated, it has very good opinions.
• For example, Does your application need an embedded web server? With Spring applications, you’ll need to decide for yourself, and if so, choose which web server to embed and make all the configuration choices manually—including for security.
• With Spring Boot, if the app needs a web server, Spring Boot installs and configures one automatically.

Key Differences

The key differences between Spring and Spring Boot involve a tradeoff between complexity and ease of use.

Spring is almost infinitely configurable, but you’ll have to spend a fair amount of time making choices, selecting modules and third-party libraries to install, and then configuring those features and functions. And you’ll have to do that before making any sort of meaningful start to the coding process.

With Spring Boot you can get up and running much faster because the framework will make many of the installation and configuration choices for you. You’ll give up some customizability, but frankly, that’s rarely a problem. In almost all cases, Spring Boot is better for web development and microservices projects; in edge cases or for very large projects, you may decide to go with Spring instead.

Key Takeaways

• Spring is an incredibly robust—and complicated—framework for building enterprise Java-based applications. As with a toolbox that has every possible screwdriver, wrench, drill bit, and socket, it’s all there, but the number of choices can be overwhelming.
• Think of Spring Boot as a version of Spring that’s much easier to use—as if someone packed a small toolbox with only what you’ll need for a specific job.
• Both Spring and Spring Boot can be used to build modular applications in Java.
• Spring Boot excels when building smaller applications, such as microservices and web apps, because its simplified configurations and smart defaults get your team up and running quickly.
• If an application is going to be very large and complex, you might want to go with the more flexible Spring Framework instead.

Spring Boot Explained

Spring Boot is an open source application framework for building enterprise Java applications. Designed to help development teams get started quickly, Spring Boot builds standalone Spring applications without the sometimes tedious configuration choices that full Spring requires.

The goals of the Spring project are to create a much faster and more streamlined experience by being opinionated—that is, by using algorithms to choose which Spring modules and features to enable, and which third-party libraries to install, and then configuring them for you. It also adds a lot of non-code functionality to a Java project, such as embedded web servers, security systems, metrics, and analytics.

The current version of Spring Boot, 3.3.4 at the time of writing, requires Java 17 at a minimum and Spring Framework 6.1.13 or later. Spring Boot works with the Maven 3.6.3 and Gradle 7.x and 8.x build tools. For embedded servlets, Spring Boot works with Tomcat, Jetty, and Undertow, or any servlet 5.0+-compatible container. You’ll probably want to use GitHub as well.

The benefit of Spring Boot is that you can take advantage of the many capabilities of the Spring application framework without all of Spring’s complexities. Developers can run their projects on any Java virtual machine that’s compatible with Java 17 or later, which means there’s no need to set up a separate web server or define WAR (web application archive) files.

Instead of requiring XML configurations for setting up Java applications, Spring Boot uses application.properties, which is ideal for database-driven applications that use Oracle Database or MySQL. In fact, if your application uses MySQL, Spring Boot can automatically configure an in-memory database for you. The Spring Data JPA (Java Persistence API) can be used to work with a wide variety of data access technologies.

If you’d like to delve into the architecture, check out this example of a Spring Boot-based application.

How Does Spring Boot Work?

Spring Boot, like many Java application frameworks and other add-ins, uses dependency injection (DI) and inversion of control (IoC) to add functionality to Java programs.

DI lets an external framework—in this case, Spring Boot—provide objects and functions to the enterprise application, so the developer doesn’t need to build them. All the developer needs to know, or define, depending on the circumstances, are the interfaces to those objects and functions.

IoC is where a program’s control flow is provided from an external source; in the case of Spring Boot, the developer handles the program logic, while the application framework provides the event loop and message dispatch. Special IoC containers in Spring handle dependency injection of objects and functions efficiently and with minimal effort by the developer.

Spring and Spring Boot use Java annotations. That’s a system where non-compilable tags prefixed with an @ symbol are embedded in the code and provide metadata that can be used to add functionality.

The developer loads Spring Boot by adding both the Spring dependencies and Spring Boot Starter dependencies into the new project’s Maven pom.xml or Gradel build.gradle files. From there, the developer adds the appropriate Spring Boot annotations into the code, such as @RestController for building a REST controller for web services. Spring Boot adds many facilities that greatly simplify the design and coding of the application; for example, it provides integration with three JSON mapping libraries, such as using Jackson to serialize and deserialize code. The Spring Security facilities are essential for building any sort of application that uses HTTP or forms—or frankly, any web application.

The Spring Boot framework sets up a four-layer architecture that separates HTTP request and JSON data transfers from program business logic, and then the logic from an object representation of data from the actual representation in an external database. This architecture can be used as-is, which is ideal for building microservices, or mapped to a Model-View-Controller design pattern, which might be more suitable for a web application.

Once you’ve added all the dependencies and written the program logic, the standard Maven and Gradle run commands will start the application. Spring Boot will ensure that everything you need from the Spring Framework is installed and configured appropriately for the project. If you want to create a self-contained executable file, Spring Boot lets you create a nested JAR file directly, which you can then distribute to run in any standard JVM (Java 17 or later) or in a native image platform, such as GraalVM.

Why Is the Spring Framework Popular?

The Spring application framework makes life easier for enterprise Java developers, no matter how large or small the project. Fundamentally, it simplifies the process of setting up the scaffolding for a Java project by installing and configuring a tremendous number of modules and third-party libraries—a process that can be quite complex, depending on the application’s architecture and context. For example, if the app needs a web server or a REST endpoint for building microservices, it’s in Spring.

Going hand in hand with the productivity boost is execution efficiency. Configuring services and libraries can be tricky, and so is optimizing them for maximum speed and low memory consumption. Spring, and in particular Spring Boot, have had years of tuning so that applications start fast and shut down fast—essential in a microservices environment.

No matter the type of application, Spring Boot provides a flexible four-level architecture that provides functional separation and abstraction. For example, the database layer takes care of talking to external data sources, such as object or relational databases. The persistence layer takes care of object-relational conversion and sending CRUD (create, read, update, delete) requests to the database layer. The business layer handles program flow, while the presentation layer manages HTTP requests and JSON translation. And all that is scaffolded by Spring Boot: In effect, the dev team merely has to code in the logic, and the application is finished.

Okay, we’re oversimplifying a bit, but you get the idea.

Another reason for Spring’s popularity is its ubiquity. Yes, Spring is everywhere, and nearly every player in the Java ecosystem supports Spring and Spring Boot, with libraries, plugins, and technical documents. There are community forums, training videos, online and in-person conferences, and even certifications. So, using Spring and Spring Boot isn’t just a solid technical decision, it can be a smart move for businesses as well because talent is available.

Advantages of Spring Boot

Spring Boot offers several advantages to enterprise Java developers over using the Spring Framework itself. Generally speaking, if the project’s requirements can be met by either Spring or Spring Boot, it’s better to use Spring Boot to take advantage of the simplified setup and increased productivity. Specific advantages include:

• Accelerated development. With Spring Boot, development teams can hit the ground running. Spring Boot’s “opinionated” algorithms can detect, load, and set up the necessary modules, functions, and third-party libraries for the project. By contrast, with Spring, developers have to manually choose what to include.
• Simplified configuration. Developers who use languages such as Java, C++, and C# know that configuring all the elements of a complex application can be time-consuming and error-prone. Spring Boot does an excellent job with automatic configuration of modules and third-party libraries, which saves a lot of work. What’s more, if the modules or libraries you use change during the dev process, Spring Boot will simply adapt and change the configuration automatically.
• Built-in features for microservices. Spring Boot can be used to build any type of enterprise Java application, whether reactive, event-driven, batch, serverless, client/server, or web. However, it’s particularly strong in building microservices, with built-in patterns for service discovery, load balancing, distributed execution tracing, and real-time message streaming. Equally important, Spring Boot apps start fast and shut down fast, which is essential for microservices scalability.
• Dependency management. Dependencies are when one part of an application’s code relies on the existence and proper functioning of libraries, modules, plugins, microservices, and APIs. Spring Boot has built-in support for dependency injection (DI), which allows externally defined objects and functions to be incorporated into the application with minimal effort. That lets developers focus on their program logic instead of worrying about external resources’ specific technical details.
• Production-ready capabilities. The goal isn’t to write software. It’s to run software. The packaging and distribution of enterprise Java applications can be tricky because of a lack of widely accepted standards for packaging them up—and the same is true of applications using the Spring Framework. Spring Boot addresses that problem by letting teams choose executable JAR files or deployable WAR files. The applications can also be deployed directly into containers or run as Windows or Unix/Linux system services.
• Seamless integration. Almost by definition, an enterprise Java application needs to talk to other applications, such as databases, ERP systems, cloud apps, legacy client/server apps—you name it. Spring Boot includes many integrations right out of the box, and nearly every open source project or major software provider supplies integration tools and guidance. For example, Oracle provides and supports JDBC, UCP, and Oracle Backend for Spring Boot and Microservices, as well as a set of Spring Boot Starters for various Oracle technologies.

Spring Boot Features

Spring Boot has evolved over decades to better suit the needs of enterprise Java developers. While the number of features may seem overwhelming, the reality is that Spring Boot’s job is to simplify. By intelligently choosing which modules, functions, and libraries to include in a project, developers can focus more on the program logic, less on infrastructure, plumbing, and scaffolding.

Here are a few of Spring Boot’s features that help simplify the development process.

• Autoconfiguration. Spring Boot’s opinionated approach determines which modules and external libraries to use with a project, and then automatically configures them. That saves developers countless hours in not only choosing those modules and libraries, but in learning how to configure them for the application context, a process that can be quite time-consuming and error-prone.
• Standalone executable JARs. One of Spring Boot’s most important features is its ability to create standalone executive JAR (Java archive) files that can be distributed directly to the runtime environment. The JAR includes all the Java class files and metadata as well as any images and other resources needed to run the standalone applications.
• Embedded web servers. If the enterprise Java app requires an HTTP server, Spring Boot installs and configures that server automatically, and with strong default security options. Available servers include Tomcat, Jetty, and Undertow.
• Spring Boot Starters. An enterprise application will have many libraries and dependencies for web servers, analytics tools, debuggers, design patterns, persistence, communications, mocking, load balancing, and so on. A Spring Boot Starter is a way to bundle all those into a single configuration file to simplify the process, reduce the amount of code, and ensure that nothing gets forgotten. It’s one-stop shopping.
• Externalized configuration. Spring Boot makes it easy to run an application’s code in different environments. The externalized configuration lets you tailor dozens of properties, including command-line arguments, properties files, and environment variables, specific to a runtime environment and encapsulate them within a single file that’s loaded at runtime and accessed via @ annotations.
• Spring Boot dev tools. Developers creating enterprise Java applications can use their favorite toolchain, including the IDE, DevOps tools, source-code management, and so on. In addition, Spring Boot includes extra tools, which can be loaded or not, at the developer’s preference, to assist with error management, logging, remote execution, and classpath administration.
• Spring Boot Actuator. The Spring Boot Actuator lets you define endpoints that can be monitored during runtime to determine the application’s health. Those endpoints can be enabled, disabled, and exposed using HTTP or JMX (Java Management Extensions); typically, you’d watch them using your favorite application management tool to see if the application is doing well, or if it’s running out of memory, stalling out, slowing down, throwing exceptions, or otherwise is in trouble.
• Simplified dependency management. Arguably the greatest strength of the Spring Boot framework is that it lets developers largely avoid manual configuration of dependencies. Spring Boot’s facilities for simplified dependency management can autoconfigure the needed modules and libraries, use Spring Boot Starters to package up libraries, and pack up apps using standalone executable JARs.
• Production-ready features. Once an application is ready to deploy, Spring Boot offers several capabilities that can help. These include Spring Boot Starters to package up all the configurations, standalone executable JARs for distributing the app, and Spring Boot Actuators to provide runtime health monitoring.

Why Is Spring Boot So Popular?

Benefits extend from development to deployment of applications.

Popular Spring Boot Features

Development:

• Autoconfiguration
• Spring Boot dev tools
• Simplified dependency management
• Embedded web servers

Deployment:

• Standalone executable JARS
• Spring Boot starters
• Externalized configuration
• Spring Boot Actuator
• Production-ready features

Spring Boot Architecture

Spring Boot can be used to help write any sort of enterprise Java application, large or small, whether it’s a streamlined microservice, a complex business-critical application to run on-premises, or a modern cloud application. A typical Spring Boot application contains four layers, which can be tailored to the needs of the application. A simple microservice, for example, may not have a database or persistence layer.

From the bottom up, here are the four layers:

• Database layer. The actual database or databases used to drive the applications and that are used for CRUD operations. You can pretty much use any extensible database with Spring Boot.
• Persistence layer. The persistence layer provides an object-relational abstraction of the actual database layer. The application logic deals with the persistence layer by interacting with business objects; the persistence layer’s code then converts those to relational rows/columns and passes the CRUD operation to the database layer.
• Business layer. Here’s where a development team solves the organization’s problem. The business layer includes the program flow as well as instructions for event handling. It communicates with users and external applications in the presentation layer and with data via the persistence layer.
• Presentation layer. The presentation layer of a Spring Boot application talks to the outside world via HTTP and JSON. Requests that come in are authenticated here, and the JSON is unpacked. Service requests are then passed to the business layer for handling. External interfaces to the application are referred to as “Views.”

Set Up Spring Boot

Ready to give Spring Boot a try? It’s easy to set it up—and that’s perhaps why so many development teams are using Spring Boot, and why students are learning this popular application framework. Anyone looking to get started should check out the open source project’s official Developing Your First Spring Boot Application documentation, but here’s a summary of the steps:

1. Ensure that you’re running Java 17 or later.
2. Configure Maven or Gradle and define the Maven pom.xml or Gradle build.gradle file to include the Spring Boot application framework.
3. Add the classpath dependencies for the Spring Boot Starter, which manages the dependencies specific to your project.
4. Write your code, which might be a simple “Hello World” or a huge business-critical application, with the proper annotations to include Spring Boot’s functionality.
5. Run the application locally using Maven or Gradle and confirm that it works to your satisfaction.
6. Package up the application in a standalone executable JAR that you can distribute, if necessary.

If you want to try out the service, check out CloudBank, an application that uses most of the services deployed.

Using Oracle Technologies with Spring Boot

Spring Boot’s database layer is compatible with a wide range of cloud and on-premises databases; two popular choices are Oracle Database and MySQL. Oracle’s developer teams are committed to supporting Spring Boot by contributing code back to the open source library and by integrating Oracle’s many frameworks and libraries. You can also find supported Spring starters for Oracle Database and OCI Services in the Oracle Cloud Marketplace.

Oracle Backend for Microservices and AI, a new platform launched in June 2024, provisions a “backend as a service” with Oracle Database and other infrastructure components that operates on multiple clouds to allow developers to build and deploy microservices in Spring Boot and other frameworks. It simplifies the task of building, testing, and operating microservices platforms and includes an AI Sandbox (developer review) for rapid iteration and experimentation with RAG and agentic techniques with Oracle Database 23ai. The AI Sandbox can generate Spring AI Microservice code that can be managed and deployed on Oracle Backend for Microservices and AI, which provides a command-line interface, a Visual Studio Code (VS Code) plugin, an IntelliJ plugin, service discovery, and event management.

Bottom line, Spring Boot is the smart open source choice. It allows your development team to write complex business applications much faster than using the Spring Framework alone. Because Spring Boot intelligently installs features, functions, and external libraries and then autoconfigures them, your developers can focus on solving the business problem, where the real value of the application is realized.

Spring Boot FAQs

What is Spring Boot and why is it used?

Spring Boot is an application framework that lets Java developers take advantage of the Spring Framework’s powerful four-layer architecture but is significantly easier to use. The benefits are improved developer productivity, reduced time to deployment, and less chance of errors due to Spring Boot’s autoconfiguration features.

Is Spring Boot a back-end framework?

Spring Boot is a framework for building enterprise Java applications. It’s suitable for cloud and on-premises deployment and for creating web, microservices, and client/server software. Spring Boot encompasses both front-end (presentation and business logic) and back-end (persistence abstraction and database connectivity) functionality.