Problem Details for standard error format in Spring Boot - Mini Project: Build & Apply

Problem Details for Standard Error Format in Spring Boot

📖 Scenario: You are building a Spring Boot REST API for a bookstore. When a client requests a book that does not exist, you want to return a clear and standard error response using the Problem Details format (RFC 7807).

🎯 Goal: Create a Spring Boot controller that returns a ProblemDetail response with a standard error format when a book is not found.

📋 What You'll Learn

Create a simple data structure to hold book information

Add a configuration variable for the error message

Implement a controller method that returns a ProblemDetail error when the book is missing

Complete the controller with proper annotations and response type

💡 Why This Matters

🌍 Real World

APIs often need to return clear, standardized error messages so clients can understand what went wrong. Using Problem Details format helps with this clarity.

💼 Career

Knowing how to implement standard error responses in Spring Boot is a valuable skill for backend developers building REST APIs.

1

DATA SETUP: Create a Map of books

Create a Map<String, String> called books with these exact entries: "123" mapped to "Spring Boot Guide" and "456" mapped to "Java Basics".

Spring Boot

// Create a Map called books with two entries
// Your code here

Need a hint?

Use Map.of() to create an immutable map with the given entries.

2

CONFIGURATION: Add an error message variable

Create a String variable called errorMessage and set it to "Book not found".

Spring Boot

Map books = Map.of(
    "123", "Spring Boot Guide",
    "456", "Java Basics"
);

// Create a String variable errorMessage with value "Book not found"
// Your code here

Need a hint?

Just assign the exact string to the variable errorMessage.

3

CORE LOGIC: Create a method to get a book or return ProblemDetail error

Create a method getBookById that takes a String id parameter. Use books.get(id) to find the book. If the book is null, return a ProblemDetail with status 404, title set to errorMessage, and detail set to "Book with id " + id + " not found". Otherwise, return the book title.

Spring Boot

Map books = Map.of(
    "123", "Spring Boot Guide",
    "456", "Java Basics"
);

String errorMessage = "Book not found";

// Create a method getBookById(String id) that returns Object
// Return ProblemDetail with status 404 if book not found
// Your code here

Need a hint?

Use ProblemDetail.forStatus(HttpStatus.NOT_FOUND) to create the error response.

4

COMPLETION: Add Spring Boot annotations to the controller method

Annotate the class with @RestController. Annotate the getBookById method with @GetMapping("/books/{id}") and add a @PathVariable String id parameter. Ensure the method returns Object.

Spring Boot

@RestController
public class BookController {

    Map books = Map.of(
        "123", "Spring Boot Guide",
        "456", "Java Basics"
    );

    String errorMessage = "Book not found";

    @GetMapping("/books/{id}")
    public Object getBookById(@PathVariable String id) {
        String book = books.get(id);
        if (book == null) {
            ProblemDetail problem = ProblemDetail.forStatus(HttpStatus.NOT_FOUND);
            problem.setTitle(errorMessage);
            problem.setDetail("Book with id " + id + " not found");
            return problem;
        }
        return book;
    }

    // Your code here
}

Need a hint?

Use @RestController on the class and @GetMapping with @PathVariable on the method.