REST API course with Java: design contracts that others can use and maintain
Learn HTTP before hiding it behind abstractions, turn business rules into consistent resources and demonstrate each contract through tests and documentation.
- HTTP and JSON
- OpenAPI
- Security and testing
How do I learn to build REST APIs in Java?
Start with a resource, its HTTP operations and the JSON your client needs. Specify successful and invalid requests, then implement and test them in Spring Boot. Add persistence and access rules in small steps so that you can explain every response.
Design the contract before writing the controller
For a task-list API, write down three interactions: create a task, retrieve it and mark it complete. Decide which fields are required, what a missing task means and which updates are allowed. These decisions give your tests something precise to check.
A useful review covers both content and behaviour. Receiving JSON is not enough if an invalid request creates a record or a caller can alter another user’s data. The linked Spring examples give a starting point for a small service and web-layer testing; the task-list scenario here is an independent practice suggestion.
- Test missing fields and invalid values alongside the normal request.
- Check that a failed operation leaves existing data unchanged.
- Document example requests and responses so another developer can try the API.
Reference material: Spring: building a RESTful web service · Spring: testing the web layer
An API is a contract, not a collection of URLs
Before writing a controller, you will study HTTP methods, status codes, headers, JSON representation, idempotency and caching. This will help you distinguish a protocol decision from an aesthetic preference.
The exercises involve real business resources, relationships and operations. You will need to choose routes, verbs, bodies, responses and errors, and explain what would happen if the same request arrived twice.
- Clear resource names and hierarchies.
- HTTP status codes consistent with the outcome.
- Explicit input and output DTOs.
- Pagination and sorting with defensive limits.
Validation does not mean trusting
Structural validation stops incomplete inputs, but an application also needs business rules and authorisation. You will learn where to place each check and how to return a uniform error format without leaking internal details.
Global exception handling connects predictable failures with useful responses. Stack traces stay in protected logs; the client receives an identifier, a safe message and the fields they can correct.
Security for every resource
Authenticating a request is not enough. You will review authorisation by role and resource ownership, excessive data exposure, usage limits, file uploads, secrets and configuration. The exercises include flaws inspired by OWASP categories, using original scenarios and code.
You will also practise testing 401, 403 and 404 responses without revealing which resources exist, and keeping an operation that changes several tables consistent.
- Roles and permissions with positive and negative tests.
- JWT without sensitive data and with verifiable expiry.
- Rate limiting at points exposed to abuse.
- Logs without passwords, tokens or banking details.
Documentation and testing as part of development
OpenAPI describes operations, schemas, responses and security. The documentation is checked against real requests using a collection included with each project.
Controller, service, repository and integration tests have different purposes. You will learn to choose the smallest scope that provides sufficient evidence and to include edge cases before considering an endpoint complete.
A process you can repeat for every challenge
Understanding, implementing and checking are parts of the same task.
- 01
Model
Identify resources, relationships and rules.
- 02
Define the contract
Define HTTP, JSON, statuses and errors.
- 03
Protect
Apply authentication, permissions and limits.
- 04
Verify
Test and publish the OpenAPI specification.
Frequently asked questions
Specific answers about this learning pathway.
Do I need to know HTTP before starting?
No. The course explains it from the fundamentals and connects it with the behaviour you will observe in Spring MVC and the testing tools.
Is Postman used?
The projects include a portable request collection. You can use Postman or another compatible tool; alternatives using HTTP files or the command line are also explained.
Does it include OpenAPI documentation?
Yes. You will learn to describe operations, schemas, responses, errors and security, and every relevant project includes OpenAPI documentation.
Are the endpoints tested?
Yes. There are web and integration tests, covering validation, authorisation, errors and persistence. Request collections complement automated tests but do not replace them.
Can the AI tutor test my API?
No. It can review snippets and help you interpret a response or error you paste, but it does not run your project. You must check it locally using its tests and requests.
Is an API finished once GET and POST return JSON?
No. Check validation, missing resources, error responses and permissions as well as successful requests. Add repeatable tests and documentation. A working demonstration is a starting point; those checks make its behaviour easier to trust and maintain.
Sources and further reading
- Spring: building a RESTful web service — A small HTTP endpoint and JSON response in Spring. Checked 2026-09-15.
- Spring: testing the web layer — Examples of testing a Spring application and its web layer. Checked 2026-09-15.
Develop this skill in the full Java backend course
Follow the programme, exercises and projects at your own pace. Review the current price and twelve-month access terms before enrolling.
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Content updated: 2026-09-15.