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Module 2: Request Bodies & JSON (The Order Form)

📚 Module 2: Request Bodies & JSON

Focus: Moving from “Searching” to “Submitting.”

When a user wants to create a new Product, they don’t just send an ID in the URL. They send a whole packet of information (Name, Price, Description). We call this a Request Body.

🏗️ Step 1: The Request Body (The “Order Form”)

To accept complex data, we use the @RequestBody annotation.

🧩 The Analogy: The Paper Order Form

  • A customer doesn’t just shout “Product!”
  • They fill out a Form with their name, address, and credit card number.
  • They hand this form to the Waiter (The Controller).

In Code:

@PostMapping
public Product createProduct(@RequestBody Product newProduct) {
    // Spring converts the JSON into this Java object automatically!
    return productRepository.save(newProduct);
}

🏗️ Step 2: JSON (The “Digital Ink”)

The “Form” is written in JSON (JavaScript Object Notation). It’s a simple text format that looks like a Java object.

🧩 The Analogy: The Shipping Label

  • Name: “Blue Shoes”
  • Price: 49.99
  • In JSON, it looks like this:
{
  "name": "Blue Shoes",
  "price": 49.99
}

🏗️ Step 3: Response Entities (The “Feedback”)

When you finish an order, you don’t just walk away. You give the customer a Receipt and a Status.

  • 200 OK: “Here is your data.”
  • 201 Created: “I successfully built your new item.”
  • 404 Not Found: “I couldn’t find what you asked for.”
  • 500 Error: “The kitchen is on fire!”

In Code:

@GetMapping("/{id}")
public ResponseEntity<Product> getProduct(@PathVariable Long id) {
    return productRepository.findById(id)
        .map(product -> ResponseEntity.ok(product)) // Return 200
        .orElse(ResponseEntity.notFound().build()); // Return 404
}

🥅 Module 2 Review

  1. @RequestBody: Accepting a whole object from a user.
  2. JSON: The text format for sharing data.
  3. ResponseEntity: Controlling the “Status Code” of your answer.
  4. Automatic Conversion: Spring (using a tool called Jackson) turns JSON text into Java Objects instantly.