How Spring Boot differs from plain Java
Spring on its own is a large, flexible platform, but every project on it used to require a lot of manual configuration. Spring Boot removed that routine: it picks sensible defaults and lets you change only what you actually need. In practice this means:
- the application runs as a single program with an embedded web server, with no separate application server;
- connecting a database, cache, message queue or email is a matter of adding a ready-made module and a few lines of configuration;
- built-in health checks, metrics and logs that are easy to connect to monitoring systems;
- a consistent project structure, so a developer who knows Spring Boot quickly understands someone else's code.
Spring Boot advantages
- Mature ecosystem. Dedicated modules for databases, authentication and authorization (Spring Security), integrations and queues are all well documented and used by large companies.
- Security as a dedicated module. Corporate account sign-in, tokens for mobile apps and permissions down to individual API methods are configured with standard tools.
- Convenient database access. Standard data operations take very little code, and complex queries can be hand-optimized.
- Ready for high load. The application is easy to run in multiple instances, and message queue modules help distribute the work.
Drawbacks and risks
- Lots of "magic." Auto-configuration is convenient as long as everything works. When something goes wrong, an inexperienced developer has a hard time figuring out where the behavior comes from.
- Memory and startup time. A Spring Boot application is usually heavier than an equivalent in Go or Node.js. For a system with dozens of small services, that means significant server costs.
- Major version upgrades are hard. Moving from version 2 to version 3 of the framework required a newer Java version and renaming packages in code and libraries. On large projects that's a separate stage of work.
- Not for small tasks. For a simple website or a small service, Spring Boot adds unnecessary complexity and more expensive maintenance.
When another framework is a better fit
If your team writes the frontend in TypeScript and wants one language across the project, NestJS on Node.js offers a similarly structured architecture. If your company's infrastructure is built on Microsoft products, ASP.NET Core is the more natural choice. And for a small product where speed to launch matters more than scale, lighter PHP or Python frameworks are more efficient.
One system or microservices
Spring Boot is often associated with microservices, systems split into many independent parts. That's genuinely useful when several teams work on a product and parts of the system have different loads. But microservices add work: network failures, distributed data, and more complex testing and deployment.
That's why we often recommend starting with a modular monolith: a single application with clearly separated modules that own their data. It's easier to develop and maintain, and when a module really does need to be split out, the boundaries are already in place.
Spring Boot and the frontend
Spring Boot typically handles only the backend and serves data through an API. The user interface is built separately in React, Angular or Vue, and the mobile app natively or cross-platform. This separation lets you change the design and add new client apps without touching the business logic on the server.
For internal tools where design isn't the priority, server-side page rendering can be enough; it's cheaper and simpler to maintain.
Deployment, monitoring and upgrades
We package Spring Boot applications as Docker images and set up automated testing and deployment after every change. How this works is described on our CI/CD and containerization page.
Spring Boot has built-in health and metrics endpoints. We connect them to Prometheus and Grafana to track memory usage, response times and errors before users report a problem. Learn more in the monitoring and reliability section.
If the project already exists
Sometimes a Spring project has been developed by different teams for years. The typical picture: an old framework version, some configuration still in XML files from the days of "classic" Spring, libraries that haven't been updated in a long time, and few tests.
We start with an audit: which dependencies are outdated or have known vulnerabilities, where there's the most manual configuration, and which areas break most often. Then we put together a gradual upgrade plan: first tests for critical scenarios, then library and Java version upgrades, and only after that the move to a new Spring Boot version. The system keeps running throughout.
What affects cost
- Architecture: a modular monolith or several separate services with their own databases and queues.
- Security and access: number of roles, corporate sign-in, audit logging, security team requirements.
- Integrations: how many external systems, and whether reliable message delivery between them is required.
- Infrastructure: on-premises servers, cloud, Kubernetes, fault-tolerance requirements.
- Existing code: for improvements, the Spring Boot and Java versions, tests and the number of outdated dependencies.
We break a large project into stages with a working result in each, so you stay in control of budget and priorities.
FAQ
Do we have to use microservices? No. For most projects, a modular system in a single application is simpler and cheaper, and it can be split up later.
Our project is on Spring Boot 2. Should we upgrade? Yes, old versions stop receiving security fixes. We estimate the scope based on dependencies and upgrade in stages.
Can Spring Boot be used with Kotlin? Yes, the framework officially supports Kotlin. It can be used in a new project or introduced gradually into an existing one.
Is Spring Boot a good fit for a startup? If the product is complex from the start and targets enterprise clients, yes. For quickly validating an idea, lighter technologies are usually a better value.
Why Promodex
With complex backend systems, we don't overpromise: we tell you honestly where Spring Boot makes sense and where a simpler solution will do. Promodex is a team of 30+ people with 750+ projects since 2015; the work is done by our own team, not hired freelancers. You know the scope and goal of every stage in advance, and after launch we support the system and keep it updated along with the framework.
