Choose one user journey
A full-stack feature connects browser interaction, server-side rules and persisted data. Start with a narrow workflow—such as creating and listing tasks—rather than trying to build an entire product at once. Write down what a user does, what data the application needs and what should happen when something goes wrong.
Agree on the API contract before wiring the UI: route, HTTP method, request fields, response fields and expected status codes. This contract lets the React and Spring Boot portions be implemented and tested independently, then integrated with fewer surprises.
Implement the backend behavior
In Spring Boot, define request and response DTOs. Validate user input at the boundary, apply business rules in a service and persist records through a repository. Return a useful status for success and known failure cases. Keep authorization checks on the server; a disabled button in the browser is not a security boundary.
Write tests for the service rule and the endpoint contract. Include invalid input and missing-resource cases. For database-backed behavior, an integration test can verify that records are actually saved and retrieved as expected.
Implement the React interaction
Build reusable components for the form and result list. Track the values needed to render the page, and avoid maintaining redundant state that can disagree. When the user submits, send JSON using the documented API contract and prevent confusing repeated submissions where appropriate.
Every asynchronous operation should account for loading, success, empty and error states. Show validation feedback near the relevant field. If the server rejects a request, preserve user input and provide a clear next step. Test keyboard navigation and responsive layout as part of feature completion.
Integrate and debug systematically
Use browser developer tools to inspect the request URL, headers, payload and response. Check the Spring logs for the corresponding request and trace errors from the boundary inward. A cross-origin issue may require a carefully configured development setup; do not solve it by allowing every origin in production.
Test one end-to-end scenario: load the list, submit valid data, see the new record, then test invalid data and a server error. Ensure the UI does not report a successful save when the API failed.
Keep the result understandable
Document how to start both applications, configure the database and run tests. Never put passwords or API secrets in frontend code or commit them to the repository. A well-scoped feature with a clear README and explainable trade-offs is a strong building block for a larger portfolio capstone.