A backend receives requests, applies business rules and reads or writes data. Java backend work also includes tests, error handling, authorization and operational visibility.
Before you begin
Be comfortable with variables, conditions, loops and basic methods. Use a small local project with a recorded JDK version and keep the input data fictional.
Work through the idea
Write the expected behavior before implementing the exercise. Keep the first version small enough to trace manually, then change one input or requirement. Record both the successful path and an invalid or empty-input case so that the result demonstrates reasoning rather than a copied output.
- Trace a request across layers
- Separate business logic from transport
- Define data and error contracts
Practice task
Design a fictional library lending endpoint with a clear unavailable-book response.
Check your result
Show the request, validation, business rule, database operation and response.
A mistake to avoid
Do not treat a controller containing all logic as the only possible architecture.
Keep a review note
Save the inputs or scenario, your reasoning and the result you checked. Explain one assumption and one case that needs more work. Revise the exercise after feedback and distinguish what you demonstrated from what remains untested.
Official reference for further study
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