--- title: "Java and Kotlin Development for JVM Backends" canonical: https://wavect.io/services/java-kotlin-development/ language: en description: "Scoped Java and Kotlin backend changes with explicit API contracts, Java interop, persistence behavior and tested JVM, build and dependency compatibility." image: "https://wavect.io/img/general/bak/open_graph_preview.jpg" --- Java & Kotlin Backend Development # Change a JVM backend without losing its business rules. The difficult part of an established Java or Kotlin service is often the behavior outside the happy path: a nullable Java value, a partial database update or a dependency upgrade that changes serialization. We make those contracts visible before changing implementation. THE ENGAGEMENT ## Preserve the rules that callers and stored data rely on. 1. **Inspect contracts** Identify API behavior, Java/Kotlin boundaries and persistence rules. 2. **Implement deliberately** Change the selected path with compatible builds and meaningful regression checks. 3. **Accept and transfer** Verify the target runtime and give maintainers the release and recovery notes. DIRECT ANSWER Wavect implements bounded Java and Kotlin backend changes on the JVM, with contract checks, persistence tests and build compatibility. Framework support and upgrade scope are confirmed against the actual codebase. Best for - Existing Java or Kotlin backend services needing a defined change - Teams addressing JVM dependency or interoperability risk Consider another approach - Native Android application development - An assumed full application rewrite ## Identify the service operation and its consumers We map the affected endpoint or job, authentication, serialization, error responses and the callers that depend on them. Existing behavior and intended changes become explicit acceptance criteria. The review includes the actual framework and libraries; Java or Kotlin does not automatically imply Spring. This page owns JVM backend work. Native Android interfaces and device behavior belong to [Mobile App Development](/services/mobile-apps/). ## Check nullability where Java and Kotlin meet Kotlin’s type system helps express missing values, but Java-originating platform types still need care. The [Kotlin interoperability documentation](https://kotlinlang.org/docs/java-interop.html) explains this boundary. We inspect DTOs, collections, annotations and exception behavior where the affected code crosses languages. Serialization and validation tests confirm how absent, null and invalid values reach the caller. ## Match transaction boundaries to the business operation We identify which database changes belong together, when they commit and how failures are reported. Persistence work may include query changes, schema evolution, transaction tests and connection handling. Isolation and retry behavior depend on the actual database, driver and framework. A database transaction does not automatically include an external API call; mixed effects need a separate consistency decision. ## Illustrative check: a failed update preserves the agreed data rule A test interrupts an operation between two related database updates. The expected transaction behavior leaves a valid state, returns the agreed error and permits a safe next attempt. Fixtures also exercise a nullable value entering from Java. These are illustrative checks, not client outcomes. For upgrades, we record JDK, compiler, build-tool and dependency compatibility, then run the same service contracts on the target setup. Whole-system replacement belongs to [Legacy Modernization](/services/legacy-modernization/). ## Deliver an incremental change with traceable engineering scope Deliverables include implementation, build changes, persistence or contract fixtures, release notes and the recovery approach for the actual data changes. Repository ownership stays with your team; the service maintainer and continuing support scope are named. [Polity](/case-studies/polity/) lists Java/Kotlin in the environment where Wavect contributed QA, review and delivery modernization. That evidence concerns this role, not original authorship of the JVM backend. Ongoing validation can continue through [Software QA](/services/software-quality-assurance/). ## Questions before you start ### Does this include Spring development? Framework support is confirmed after reviewing your application and the expertise its scope requires. The Java/Kotlin offer is not a claim of universal experience with every JVM framework. ### Must we convert Java code to Kotlin? No. A mixed codebase can remain appropriate. Conversion needs a specific benefit and checks around callers, nullability, builds and maintenance; it is not a default deliverable. ### Can a runtime upgrade be treated as a small configuration edit? Sometimes, but it must be verified. Compiler targets, removed APIs, build plugins and library behavior may affect the change. We agree a supported version path and regression scope first. ### Can deployment rollback undo database changes? Not automatically. Data and schema changes need their own compatibility and recovery plan. We document what can be reversed, what must be repaired forward and who approves the decision. ## Continue with the right scope - [Plan broader system modernization](/services/legacy-modernization/) - [Verify existing business behavior](/services/software-quality-assurance/) - [Develop native mobile applications](/services/mobile-apps/) ## Structured Data ```json { "@context": "https://schema.org", "@graph": [ { "@id": "https://wavect.io/#organization", "@type": [ "Organization", "ProfessionalService", "LocalBusiness" ], "employee": [ { "@id": "https://wavect.io/team/kevin-riedl/#person", "@type": "Person", "jobTitle": "Managing Director", "name": "Kevin Riedl", "url": "https://wavect.io/team/kevin-riedl/", "worksFor": { "@id": "https://wavect.io/#organization", "@type": [ "Organization", "ProfessionalService", "LocalBusiness" ] } }, { "@id": "https://wavect.io/team/christof-jori/#person", "@type": "Person", "jobTitle": "Managing Director", "name": "Christof Jori", "url": 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