Spring Boot: Developer — Lesson 2: REST controllers, request mapping, validation, exception handling, serialization, DTOs, service layers, API design, documentation, and integration testing

Learning Objectives

• Translate a realistic infrastructure or application requirement into an executable approach for REST controllers, request mapping, validation, exception handling, serialization, DTOs, service layers, API design, documentation, and integration testing.
• Use tested REST API and error-response contract to verify configuration, connectivity, security, and expected behavior.
• Explain how to recover safely when invalid input returning an internal error instead of a stable client response occurs.

Detailed Topics

• REST controllers
• Request mapping
• Validation
• Exception handling
• Serialization
• DTOs
• Service layers
• API design
• Documentation
• And integration testing
• Decision ownership, prerequisites, and acceptance evidence for REST controllers, request mapping, validation, exception handling, serialization, DTOs, service layers, API design, documentation, and integration testing
• Relevant access, security, capacity, dependency, performance, recovery, and support considerations

Instructor Demonstration

Using realistic infrastructure, identities, and workloads, the instructor demonstrates REST controllers, request mapping, validation, exception handling, serialization, DTOs, service layers, API design, documentation, and integration testing. Checkpoints are captured in tested REST API and error-response contract, with discussion of alternatives, side effects, and acceptance conditions.

Hands-On Exercise

Work through a role-based scenario involving REST controllers, request mapping, validation, exception handling, serialization, DTOs, service layers, API design, documentation, and integration testing. Validate the expected path, test “invalid input returning an internal error instead of a stable client response,” choose the safest corrective action, and capture the reasoning and outcome in tested REST API and error-response contract.

1. Define the requirement and identify dependencies before changing the environment.
2. Create a baseline result that can be compared with later changes.
3. Reproduce the exception and test one hypothesis at a time.
4. Complete the evidence record and obtain peer or instructor review.

Scenario Analysis

• Clarify the service trigger, affected components and roles, prerequisites, and acceptable result for REST controllers, request mapping, validation, exception handling, serialization, DTOs, service layers, API design, documentation, and integration testing.
• Compare at least two implementation or correction choices and identify which evidence would distinguish them.
• Decide how tested REST API and error-response contract should be reviewed, approved, retained, and handed to the next owner.

Troubleshooting Guidance

For a failure in REST controllers, request mapping, validation, exception handling, serialization, DTOs, service layers, API design, documentation, and integration testing, separate access, configuration, compute, network, storage, integration, and timing causes. Compare the observed sequence with tested REST API and error-response contract; if “invalid input returning an internal error instead of a stable client response” is confirmed, document why broader changes were rejected.

Validation Checklist

• Configuration and source state used for REST controllers, request mapping, validation, exception handling, serialization, DTOs, service layers, API design, documentation, and integration testing are versioned or otherwise traceable.
• Tested rest api and error-response contract shows both baseline and accepted result.
• Security, performance, dependency, and resilience side effects are considered where relevant.
• Recovery steps and handover notes are usable by an operations practitioner.

Lesson Outcome

Learners can apply REST controllers, request mapping, validation, exception handling, serialization, DTOs, service layers, API design, documentation, and integration testing, explain the decisions made, and defend the result with tested REST API and error-response contract.