Handling path variables and query params together in Spring Boot - Mini Project: Build & Apply

Handling path variables and query params together in Spring Boot

📖 Scenario: You are building a simple Spring Boot web service for a bookstore. You want to create an endpoint that takes a book category as a path variable and an optional filter as a query parameter.This will help users get books from a specific category and optionally filter them by author name.

🎯 Goal: Build a Spring Boot controller with a method that handles a path variable category and an optional query parameter author. The method should return a string message showing the received category and author filter.

📋 What You'll Learn

Create a Spring Boot controller class named BookController

Add a GET mapping method named getBooksByCategory

Use @PathVariable to get the category from the URL path

Use @RequestParam to get the optional author query parameter with default value "all"

Return a string message showing the category and author filter values

💡 Why This Matters

🌍 Real World

Web services often need to get data from both the URL path and query parameters to filter or customize responses.

💼 Career

Understanding how to handle path variables and query parameters is essential for backend developers building REST APIs with Spring Boot.

1

Create the controller class and method signature

Create a public class named BookController annotated with @RestController. Inside it, create a public method named getBooksByCategory that returns a String. Add a @GetMapping annotation with the path "/books/{category}".

Spring Boot

@RestController
public class BookController {
    
    // Create getBooksByCategory method with @GetMapping("/books/{category}")
    // Your code here
}

Need a hint?

Use @RestController on the class. Use @GetMapping("/books/{category}") on the method. The method should return a String.

2

Add the path variable parameter

Modify the getBooksByCategory method to accept a String parameter named category annotated with @PathVariable.

Spring Boot

@RestController
public class BookController {
    
    @GetMapping("/books/{category}")
    public String getBooksByCategory(@PathVariable String category) {
        // Your code here
        return "";
    }
}

Need a hint?

Add @PathVariable String category as a parameter to the method.

3

Add the optional query parameter

Add a second parameter to getBooksByCategory named author of type String. Annotate it with @RequestParam with required = false and defaultValue = "all".

Spring Boot

@RestController
public class BookController {
    
    @GetMapping("/books/{category}")
    public String getBooksByCategory(@PathVariable String category, @RequestParam(required = false, defaultValue = "all") String author) {
        // Your code here
        return "";
    }
}

Need a hint?

Use @RequestParam(required = false, defaultValue = "all") String author as the second parameter.

4

Return a message showing category and author

In the getBooksByCategory method, return a string formatted as "Category: {category}, Author filter: {author}" using string concatenation or String.format.

Spring Boot

@RestController
public class BookController {
    
    @GetMapping("/books/{category}")
    public String getBooksByCategory(@PathVariable String category, @RequestParam(required = false, defaultValue = "all") String author) {
        // Your code here
        return "";
    }
}

Need a hint?

Use return String.format("Category: %s, Author filter: %s", category, author); to create the message.