Request mapping by method and path in Spring Boot - Mini Project: Build & Apply

Request Mapping by Method and Path in Spring Boot

📖 Scenario: You are building a simple web service for a bookstore. The service needs to respond differently based on the HTTP method and the URL path.

🎯 Goal: Create a Spring Boot controller that maps requests by HTTP method and path. You will define a controller class, configure a base path, add methods to handle GET and POST requests at specific paths, and complete the controller with proper annotations.

📋 What You'll Learn

Create a controller class named BookController

Add a base request mapping path /books to the controller

Add a method to handle GET requests at path /list

Add a method to handle POST requests at path /add

Use correct Spring annotations for request mapping by method and path

💡 Why This Matters

🌍 Real World

Web services often need to respond differently based on HTTP method and URL path. This project shows how to set up those mappings in Spring Boot.

💼 Career

Understanding request mapping is essential for backend developers working with Spring Boot to build REST APIs.

1

Create the controller class

Create a public class named BookController annotated with @RestController.

Spring Boot

@RestController
public class BookController {
    // Your code here
}

Hint

Use @RestController above the class to make it a REST controller.

2

Add base request mapping path

Add a class-level @RequestMapping annotation with the path /books to the BookController class.

Spring Boot

@RestController
@RequestMapping("/books")
public class BookController {
    // Your code here
}

Hint

Use @RequestMapping("/books") above the class to set the base path.

3

Add GET method for listing books

Inside BookController, add a public method named listBooks that returns a String. Annotate it with @GetMapping("/list").

Spring Boot

@RestController
@RequestMapping("/books")
public class BookController {
    // Your code here
}

Hint

Use @GetMapping("/list") to map GET requests to /books/list.

4

Add POST method for adding a book

Inside BookController, add a public method named addBook that returns a String. Annotate it with @PostMapping("/add").

Spring Boot

@RestController
@RequestMapping("/books")
public class BookController {
    @GetMapping("/list")
    public String listBooks() {
        return "Listing all books";
    }
    // Your code here
}

Hint

Use @PostMapping("/add") to map POST requests to /books/add.

Practice

1. What does the @RequestMapping annotation do in Spring Boot?

easy

A. It styles the HTML page returned by the controller.

B. It creates a new database connection automatically.

C. It links a URL path and HTTP method to a specific method in a controller.

D. It schedules background tasks to run periodically.

Solution

1. Step 1: Understand the purpose of @RequestMapping

   @RequestMapping is used to connect web requests to controller methods in Spring Boot.

2. Step 2: Identify what it links

   It links both the URL path and the HTTP method (GET, POST, etc.) to the method that should handle the request.

3. Final Answer:

   It links a URL path and HTTP method to a specific method in a controller. -> Option C

4. Quick Check:

   @RequestMapping links URL and method [OK]

Hint: Remember: @RequestMapping connects URL + HTTP method to code [OK]

Common Mistakes:

• Thinking @RequestMapping styles HTML output
• Confusing it with database or scheduling annotations
• Assuming it only maps URL without HTTP method

2. Which of the following is the correct way to map a GET request to path "/home" using @RequestMapping?

easy

A. @RequestMapping(route = "/home", method = GET)

B. @RequestMapping(path = "/home", method = RequestMethod.GET)

C. @RequestMapping(value = "/home", type = "GET")

D. @RequestMapping(method = "GET", url = "/home")

Solution

1. Step 1: Recall correct @RequestMapping syntax

   The correct syntax uses 'path' or 'value' for URL and 'method' with RequestMethod enum for HTTP method.

2. Step 2: Match options with syntax

   @RequestMapping(path = "/home", method = RequestMethod.GET) uses path and method=RequestMethod.GET correctly. Others use invalid attribute names or wrong types.

3. Final Answer:

   @RequestMapping(path = "/home", method = RequestMethod.GET) -> Option B

4. Quick Check:

   Correct syntax [OK]

Hint: Use 'path' and RequestMethod.GET for GET mapping [OK]

Common Mistakes:

• Using 'url' instead of 'path' or 'value'
• Passing HTTP method as string instead of RequestMethod enum
• Using wrong attribute names like 'route' or 'type'

3. Given this controller method:

@RequestMapping(path = "/test", method = RequestMethod.POST)
public String test() {
    return "Success";
}

What happens when a client sends a GET request to "/test"?

medium

A. The server crashes with an exception.

B. The method runs and returns "Success".

C. Spring returns a 404 Not Found error.

D. Spring returns a 405 Method Not Allowed error.

Solution

1. Step 1: Identify the mapped HTTP method

   The method is mapped only to POST requests at path "/test".

2. Step 2: Understand what happens on GET request

   A GET request to the same path is not handled, so Spring returns 405 Method Not Allowed.

3. Final Answer:

   Spring returns a 405 Method Not Allowed error. -> Option D

4. Quick Check:

   GET to POST-only path = 405 error [OK]

Hint: GET request to POST-only path causes 405 error [OK]

Common Mistakes:

• Assuming GET runs the POST method
• Thinking it returns 404 Not Found instead
• Believing server crashes on wrong method

4. What is wrong with this mapping?

@RequestMapping(path = "/data", method = "POST")
public String saveData() {
    return "Saved";
}

medium

A. The method attribute should use RequestMethod.POST, not a string.

B. The path attribute cannot be used with @RequestMapping.

C. The method must return void, not String.

D. The method name must be saveDataPost, not saveData.

Solution

1. Step 1: Check method attribute type

   The method attribute expects a RequestMethod enum value, not a string.

2. Step 2: Identify correct usage

   Using method = "POST" is invalid; it should be method = RequestMethod.POST.

3. Final Answer:

   The method attribute should use RequestMethod.POST, not a string. -> Option A

4. Quick Check:

   method attribute needs RequestMethod enum [OK]

Hint: Use RequestMethod.POST enum, not string "POST" [OK]

Common Mistakes:

• Passing HTTP method as string instead of enum
• Thinking path attribute is invalid
• Assuming return type or method name causes error

5. You want to create two methods in a controller: one handles GET requests at "/items" and another handles POST requests at the same path "/items". Which is the best way to do this?

hard

A. Use two methods with @RequestMapping(path = "/items", method = RequestMethod.GET) and @RequestMapping(path = "/items", method = RequestMethod.POST).

B. Use one method with @RequestMapping(path = "/items") and check HTTP method inside the method manually.

C. Use @RequestMapping(path = "/items") on both methods without specifying method attribute.

D. Use @RequestMapping(method = RequestMethod.GET) on one method and @RequestMapping(method = RequestMethod.POST) on the other without path.

Solution

1. Step 1: Understand how to map same path with different methods

   Spring allows multiple methods mapped to the same path but different HTTP methods using method attribute.

2. Step 2: Evaluate options

   Use two methods with @RequestMapping(path = "/items", method = RequestMethod.GET) and @RequestMapping(path = "/items", method = RequestMethod.POST). correctly uses two methods with same path but different HTTP methods. Use one method with @RequestMapping(path = "/items") and check HTTP method inside the method manually. is less clean and error-prone. Use @RequestMapping(path = "/items") on both methods without specifying method attribute. causes ambiguity. Use @RequestMapping(method = RequestMethod.GET) on one method and @RequestMapping(method = RequestMethod.POST) on the other without path. misses path, so won't map correctly.

3. Final Answer:

   Use two methods with @RequestMapping(path = "/items", method = RequestMethod.GET) and @RequestMapping(path = "/items", method = RequestMethod.POST). -> Option A

4. Quick Check:

   Separate methods with same path, different HTTP methods [OK]

Hint: Map same path with different methods by specifying method attribute [OK]

Common Mistakes:

• Not specifying method attribute causing conflicts
• Checking HTTP method manually inside one method
• Omitting path attribute causing mapping errors