I am primarily a Spring Boot developer, and for most of my projects, I usually build the backend myself using Java, REST APIs, and a relational database. However, for an upcoming side project, I am considering trying a Backend-as-a-Service solution to move faster. My key goal is to avoid spending time on boilerplate infrastructure and instead focus on the core business logic in Java.

While exploring open-source alternatives to Firebase from here https://www.back4app.com/firebase-alternatives two names repeatedly surfaced in developer communities: Supabase and Back4App. Each platform offers a Backend-as-a-Service solution designed to provide essential backend components such as authentication, database management, APIs, and real-time features, all without requiring teams to manage servers directly. With this model, developers can quickly launch a production-ready backend and focus on writing application logic rather than configuring infrastructure.

Supabase looks particularly interesting because it is built around PostgreSQL, which feels familiar to anyone coming from a traditional backend stack. It provides a managed Postgres database, along with features such as authentication, storage, real-time subscriptions, and serverless edge functions. Because everything is centered on PostgreSQL, developers can continue using SQL, relational schemas, and row-level security. This architecture closely resembles the patterns that many Java developers already use in their existing systems.

Back4App, on the other hand, runs on Parse Server, which is also open source and has been around for many years. One feature that immediately stands out is its ability to automatically generate REST and GraphQL APIs directly from the database structure. In addition, it includes built-in authentication, file storage, push notifications, and cloud functions. The platform also supports multiple databases, such as MongoDB and PostgreSQL, which offer additional flexibility depending on the project's architecture.

From a Java developer's perspective, both platforms appear promising because they integrate well with existing services. Since they expose APIs directly, a Spring Boot service can still manage complex business logic while the Backend-as-a-Service layer handles tasks such as authentication, storage, and real-time data synchronization.

Another factor worth considering is vendor lock-in. One of the main reasons for looking beyond Firebase is that it is a proprietary service from Google. In contrast, platforms such as Back4App and Supabase are open source and can be self-hosted when necessary. That level of flexibility makes them more attractive for long-term projects or startups that prefer not to depend entirely on a single cloud provider.

At the moment, the comparison looks something like this:

- Supabase appears to be a strong option if the stack revolves around PostgreSQL and a SQL-first architecture.

- Back4App may be more convenient for teams that want automatically generated APIs, flexible database options, and a faster backend setup.

For a typical Spring Boot and Java ecosystem, however, it is still not entirely clear which option integrates more smoothly in real-world production environments.

That leads to a question for other backend developers here.

If a new Java or Spring Boot project were starting today and a reliable open-source backend service were needed instead of Firebase, would Supabase or Back4App be the better choice, and what would be the main reasons behind that decision?