01Owns
Spring Boot services
Builds REST controllers, service layers and configuration with Spring Boot, using profiles and externalised properties rather than code branches for each environment.
Hire · Backend
Hire Java Developers
Senior Java engineers who join your team to work on Spring Boot services, enterprise integrations and long-lived JVM systems. Every candidate has diagnosed a lazy-loading problem in JPA and read a garbage collection log in a paid exercise before you speak to them.
Paid Spring Boot and JVM exercise
Senior and lead levels only
Fits your build, release and review process
On your team
What a Java developer owns on your team.
02Owns
Persistence with JPA
Maps entities with Hibernate, controls fetch strategies, writes JPQL or native queries where they help and manages schema changes with Flyway or Liquibase.
03Owns
JVM health in production
Sizes heaps, chooses and tunes the garbage collector, and reads thread dumps and GC logs when latency spikes.
04Owns
Enterprise integration
Connects to message brokers, SOAP and REST partners, identity providers and legacy databases, with transactions and retries that survive partial failure.
05Owns
Builds and dependencies
Keeps Maven or Gradle builds reproducible, manages dependency versions with a BOM and patches vulnerable libraries promptly.
Beyond Spring annotations
Plenty of Java developers can assemble a Spring Boot service from annotations. Far fewer can explain what those annotations do at runtime: when a transaction actually starts, why a self-invoked method skips its proxy, or how a lazy collection triggers dozens of selects during JSON serialisation. Those are the questions that separate maintainers from assemblers.
Ask candidates about a production incident they traced to Hibernate or transaction boundaries. Specific stories about fetch strategies and open-session-in-view are a strong sign.
Vetting
Skills we test before a Java developer joins.
01Tested
Spring internals
Understands dependency injection, bean scopes, auto-configuration and why @Transactional on a private method does nothing.
02Tested
Hibernate behaviour
Recognises N+1 selects from lazy associations, uses fetch joins or entity graphs and knows what open-session-in-view hides.
03Tested
Concurrency on the JVM
ExecutorService, CompletableFuture and virtual threads, plus the thread-safety rules for shared Spring beans.
04Tested
Garbage collection
Can compare G1 and ZGC for a workload, read GC logs and tell a memory leak from an undersized heap.
05Tested
Modern Java
Records, sealed types, pattern matching and the Streams API, used where they make code clearer.
06Tested
Testing
JUnit 5, Mockito where it helps, Spring Boot test slices and Testcontainers for real database and broker tests.
Work sample
How the Java developer work sample runs.
- 01Step 1
Repair a slow endpoint
The candidate gets a Spring Boot endpoint that triggers N+1 selects through lazy collections and fixes it without changing the JSON returned.
- 02Step 2
Read a memory problem
From a GC log and a heap histogram, they decide whether the service leaks or simply needs a different heap size, and explain the evidence.
- 03Step 3
Add an integration safely
They add a call to a flaky partner API with timeouts, retries and a Testcontainers-backed test. We pay for the time spent.
- 04Step 4
Brief a stakeholder
On a short call they describe a trade-off from their solution to someone who does not write Java.
Testing the JVM side, not only the code
Java services fail in ways that do not show in a code review: memory pressure, long pauses and thread pool exhaustion. That is why the exercise includes reading a GC log and a heap histogram, alongside fixing a slow endpoint and adding a resilient integration tested against real containers.
Levels
Java Developers: what changes at each level.
01Level 1
Senior
Delivers features in existing Spring Boot services and reviews peers’ persistence and transaction code.
02Level 2
Lead
Owns module boundaries, shared libraries, build conventions and the testing approach across Java services.
03Level 3
Enterprise architect
Plans Java version and framework upgrades across many services, integration patterns between systems and the move away from legacy application servers.
Picking the right Java level
A senior engineer is the right fit when your services, modules and build are already well organised. If shared libraries have sprawled and every team builds differently, a lead will consolidate them. Choose an enterprise architect when the work spans many systems, such as a JDK upgrade across dozens of services or retiring an application server.
Other options
When to hire someone other than a Java developer.
01Consider
Your stack is Microsoft
If you run on C#, SQL Server and Azure, a .NET developer fits the tooling and hosting you already have.
Open register02Consider
Lean, latency-critical services
For small network services where startup time and memory footprint dominate, Go is often a better choice.
Open register03Consider
Native Android apps
Java knowledge helps on Android, but app lifecycle, UI and Play Store work need an Android specialist.
Open registerOnboarding into an enterprise codebase
Large Java estates take time to learn, so map the territory early. In week one, have the engineer build every module locally and ship one small fix. Over the following weeks, give them a service to own and ask for a short dependency report showing outdated or vulnerable libraries. It is useful on its own and shows how they read an unfamiliar system.
FAQ
Questions to resolve before the build.
01Do your Java developers work with Spring Boot specifically?
Spring Boot is the default in our vetting because most teams use it. Candidates with strong Jakarta EE, Quarkus or Micronaut experience can be matched if that is what you run.
02Can they help with an upgrade to a newer Java version?
Yes. Leads and architects regularly plan moves between long-term support releases, which usually involve dependency upgrades, removed APIs, and Spring Boot major version changes alongside the JDK.
03Will a Java developer handle JVM tuning in production?
Senior engineers can read GC logs, thread dumps and heap histograms and adjust settings. For large estates, pair them with DevOps so container limits and JVM flags are set together.
Works alongside
Roles a Java developer works best alongside.
01Pair with
Angular developers
Many enterprise front ends are Angular on top of Spring APIs; contracts and auth flows are easier agreed together.
Open register02Pair with
DevOps engineers
For container memory limits, JVM flags in Kubernetes, and pipelines that build and scan artefacts.
Open register03Pair with
SAP developers
When Java services integrate with SAP systems for orders, finance or master data.
Open registerProduct delivery
Need the whole product built instead?
Primary sources
References behind this page
Dated official documentation, standards, and research that support the factual claims on this page.
- 01Spring Boot reference documentation
Official reference for Spring Boot configuration, features and testing.
- 02Oracle: HotSpot Virtual Machine Garbage Collection Tuning Guide
Official guidance on choosing and tuning JVM garbage collectors.
How to read this page
Scope, cost and timeline figures are planning guidance until confirmed in a written proposal. Diagrams and screens are illustrations, not client deliverables, and source-code rights and handover follow the signed agreement. See the delivery process and the full disclaimer.
Next decision
Turn the brief into an accepted product scope.
Define outcomes, constraints, evidence, rights and handover before delivery begins.
Commercial rights, repositories, environments, documentation, acceptance and handover remain contract-defined.