Week 4 - Rest APIs

Java Annotations

Introduction to REST

Spring Boot Setup

Writing Endpoints

Message Formats

Input Validation

Practice

Assignment

• Teachers

Back end Track

Content

Let’s get practical

<aside> 💭

Practice exercises are optional and do not need to be submitted

</aside>

For Exercises 1 and 2, use a small Spring Boot project with Spring Web, Lombok, and Validation if needed. You may create a fresh project for each exercise, or keep each exercise in its own feature package inside one practice project.

Exercise 1 - Design a REST API

Choose a simple resource that is either:

• An intangible resource:
  • Digital asset: e-books, music, images, or similar files
  • Information resource: weather-data, event-info, or similar data
• A tangible resource: books, clothes, tickets, or similar items

Create a markdown file named API_DESIGN.md and design the API you would build for that resource.

Requirements:

• At least four endpoints with resource-oriented URIs.
• The HTTP method and successful response status code for each endpoint.
• One example request body and one example response body.
• One example error response for invalid input or a missing resource.

Exercise 2 - Build a Service+Controller Combo

Choose one pair of resources:

• Book – Author
• Product – Category
• Task – Project

For one resource, start by writing the controller first:

• Avoid writing any business logic.
• Make an outline of your service by creating an unimplemented interface, or a class with all its methods throwing UnsupportedOperationException.
• Then implement your controller against the service interface/class.
• Test your controller through Postman.
• When the controller is working, implement the methods in your service layer.

For the other resource, start by writing the service first:

• Write your business logic and methods.
• Unit test the service component.
• When the service is working, implement the controller on top of the service layer.

API Endpoints

Limit each resource to three endpoints: GET all items, POST add a new item, and DELETE delete an item.

Reflection Questions

After implementing both approaches, answer the following:

1. Which approach let you get a working HTTP endpoint faster? Why?
2. What challenges did you come across in either approach?
3. Which approach felt more maintainable, and why?

Exercise 3.1 - Find and Handle Exceptions

Go back to the Categories API you built in Writing Endpoints. Remove any exception handlers except the handler for MethodArgumentNotValidException that we implemented in Input Validation.

Then, from Postman, try sending bad inputs to find more unhandled exceptions. Hint: There are a few.

How many can you find? Can you handle them? What would be an appropriate message?

<aside> 💡

Run your application without debug mode. This makes it easier to see thrown exceptions either in the Postman response or in the application console, near Spring Boot's startup message.

</aside>

Exercise 3.2 - More Validations

While working through the previous exercise, did you find validation scenarios that were missing?

Think in terms of:

• Long strings
• Negative numbers
• Incorrect types
• Typos
• Other intentional or accidental bad input

List them and implement the missing validations.

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