A guide to hiring a Java developer
Java is a general-purpose programming language that runs on the Java Virtual Machine. Banks, shops, logistics firms and many software companies use it for the systems that keep a business running. A Java developer builds and looks after those systems. If you need a dependable back end, a set of APIs or someone who can keep an older application healthy, this is the role to look at.
What the job covers day to day
Writing classes is only part of it. A Java developer turns a business rule into code, decides where data is stored and splits the work into services or modules that can change on their own. The week also holds code reviews, log reading and build fixes. Then there are the quiet jobs that users never see, such as start-up time, memory use and a safe way to ship each change.
Spring and Spring Boot
Spring is the most widely used framework for Java back ends, and Spring Boot makes it quick to start a service with sensible defaults. A good developer knows what Boot does for them and what it hides. They can set up configuration for each environment, wire parts together with dependency injection, secure routes with Spring Security and expose health checks for monitoring. If a company asks for a Spring Boot developer, this is the skill set they mean. Ask candidates to explain a bug that came from auto-configuration, since it shows whether they understand the framework or only copy from it.
Enterprise back ends
Large business systems have long lives. They hold rules about orders, invoices, accounts or stock, and they talk to payment providers, ERP software and other internal systems. A Java engineer who has worked on these knows how to keep transactions correct, handle retries and protect data. Where a system has grown into one large block, our microservices developers can help split it carefully, and our back end developers cover other server languages as well.
REST APIs and integrations
Most Java work meets the outside world through an API. A strong developer picks clear resource names, validates input, returns errors a client can act on and writes documentation that matches the code. For links between systems they use queues and events, with tools such as Kafka or RabbitMQ, so a slow partner does not freeze the whole app. They also plan for change, because an API that other teams depend on cannot be altered on a whim.
Databases and data access
Java apps usually sit on a relational database. Developers map tables with JPA and Hibernate, write queries and manage schema changes with migration tools. The common trap is a tidy repository method that triggers many hidden queries. A careful engineer reads the SQL that the code produces, adds the right indexes and knows when to step outside the object mapper. For heavy data work, see how our Hadoop developers handle very large datasets.
Android with Java
Many Android apps were first written in Java and are still in use. A Java developer can fix crashes, update libraries and add features to those apps. For new Android code most teams now choose Kotlin, and the two languages can live in the same project. A good engineer can read both and move one screen or module at a time. If you are weighing a move, our Kotlin developers can tell you what it would involve.
Moving old Java applications forward
Some applications still run on an old Java version, an old framework or a server nobody wants to touch. Moving them forward is a project of its own. The usual order is to add tests around what the system does today, update the build, raise the Java version in steps and replace the libraries that no longer receive fixes. Doing it in small releases keeps the business running while the code gets safer. Ask candidates about an upgrade they have done and what went wrong along the way.
Testing and quality
Java has a mature set of testing tools. JUnit and Mockito cover unit tests, and Testcontainers can start a real database in a container for integration tests. A good developer writes tests that are quick, check what the code does and survive a refactor. Maven or Gradle then run those tests on every change, so a break shows up in minutes.
Freelance Java developer or a dedicated one
Many people search for a freelance Java developer, and for a one-off script that can be a fine choice. For a product you will run for years, the picture changes. A freelancer has to be found, checked and managed, and may leave when a bigger job appears. With DigiWorks you get a dedicated remote engineer who works for your team, full time or part-time from 20 hours a week. We vet the candidates and handle the contract and pay, and you choose who starts and what they work on.
Why teams look for Java help
The reasons vary. One team needs a new service built beside a product that already earns money. Another has lost the only person who understood a Java system. A third wants an old application raised to a current Java version, and a fourth just needs more hands before a launch. Each of these asks for a slightly different engineer, so say which one is yours.
When a Java developer makes sense
- You run a business system that must stay correct and available.
- You need REST APIs or integrations with other software.
- You have a Java application that needs updates, tests or a new owner.
- You want a Spring Boot service built with a clear structure.
- You have an Android app that is still written in Java.
For a simple brochure site or a quick prototype, a lighter stack is often cheaper to build and run. An engineer who tells you so up front is on your side.
Reading a Java resume
Pick one project on the page and dig in. What did the system do, how many people depended on it and what went wrong in production? Ask the candidate to walk a request from the browser through the code to the database and back. Frameworks on a list prove little, because anyone can write Spring in a skills box. Real experience shows when a person can describe an outage in detail and the fix that kept it from coming back.
Interview questions worth asking
- How would you find out why a Spring Boot service has become slow?
- When do you choose a queue over a direct call between two services?
- How do you stop an object mapper from running too many queries?
- How would you move an old Java application to a current Java version without a long freeze?
- How do you decide what to fake and what to run for real in a test?
Listen for reasons and real stories. A person who can name every annotation but cannot explain how the code reaches production is a warning sign.
Try a small paid job
Give each finalist the same small piece of your own work. It could be a failing test, one new endpoint or a review of a class you worry about. Pay for their time. Afterwards, compare the code, the tests, the questions they asked and how clearly they explained what they did.
Setting up for the long run
Agree early on how code is reviewed, how releases go out and who answers when an alert fires. A one-page note on the layout of the app and the command that runs the tests saves hours later. Keep the repository, servers and database accounts in your company name, each person with their own login, so access is easy to change.
What to expect in week one
Hand over repository access, the build instructions and a staging copy of the app. Agree a weekly call and one shared task list. Raise the awkward corners at once, such as a class that everyone avoids or a test that fails now and then. A Java specialist is most useful there.
Mistakes to avoid
- Choosing on a framework list alone, with no sign of running a live system.
- Skipping tests because a change looks small.
- Leaving an old Java version in place until it can no longer be patched.
- Hiring someone for a quick task and expecting long-term ownership.
Related help: our software engineers suit wider product teams, and our API developers suit work where the interface comes first.