Problem Details for standard error format in Spring Boot

Introduction

Problem Details provide a simple, consistent way to show errors in web APIs. It helps clients understand what went wrong without confusion.

When your API needs to tell clients about errors clearly.

When you want to follow a common standard for error messages.

When you want to include details like error type, message, and status code.

When you want to make debugging easier for API users.

When you want to support automatic error handling in clients.

Syntax

Spring Boot

HTTP/1.1 400 Bad Request
Content-Type: application/problem+json

{
  "type": "https://example.com/probs/out-of-credit",
  "title": "You do not have enough credit.",
  "status": 400,
  "detail": "Your current balance is 30, but that costs 50.",
  "instance": "/account/12345/transactions/abc"
}

The Content-Type must be application/problem+json to follow the standard.

Fields like type, title, status, detail, and instance help describe the error clearly.

Examples

A typical JSON response showing a problem with credit balance.

Spring Boot

{
  "type": "https://example.com/probs/out-of-credit",
  "title": "You do not have enough credit.",
  "status": 400,
  "detail": "Your current balance is 30, but that costs 50.",
  "instance": "/account/12345/transactions/abc"
}

Example for a 'not found' error using the standard format.

Spring Boot

{
  "type": "https://example.com/probs/not-found",
  "title": "Resource not found.",
  "status": 404,
  "detail": "The requested item was not found in the database.",
  "instance": "/items/999"
}

Sample Program

This Spring Boot controller returns a problem detail error when the item is not found. It uses the standard format to describe the error.

Spring Boot

package com.example.demo;

import org.springframework.http.HttpStatus;
import org.springframework.http.ProblemDetail;
import org.springframework.http.ResponseEntity;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RestController;
import java.net.URI;

@RestController
public class ItemController {

    @GetMapping("/items/{id}")
    public ResponseEntity<?> getItem(@PathVariable int id) {
        if (id != 1) {
            ProblemDetail problem = ProblemDetail.forStatus(HttpStatus.NOT_FOUND);
            problem.setType(URI.create("https://example.com/probs/not-found"));
            problem.setTitle("Resource not found.");
            problem.setDetail("Item with id " + id + " was not found.");
            problem.setInstance(URI.create("/items/" + id));
            return ResponseEntity.status(HttpStatus.NOT_FOUND).body(problem);
        }
        return ResponseEntity.ok("Item 1 details");
    }
}

Important Notes

Spring Boot 3+ supports ProblemDetail class to create standard error responses easily.

Always set the Content-Type header to application/problem+json for clients to recognize the format.

Use meaningful type URIs to help clients find more info about the error.

Summary

Problem Details standardize error messages in APIs for clarity.

Use fields like type, title, status, detail, and instance.

Spring Boot provides built-in support to create these error responses easily.

Practice

1. What is the main purpose of using Problem Details in Spring Boot APIs?

easy

A. To standardize error messages for better clarity and consistency

B. To speed up API response times

C. To encrypt API responses for security

D. To generate API documentation automatically

Solution

1. Step 1: Understand the role of Problem Details

   Problem Details format is designed to provide a consistent structure for error messages in APIs.

2. Step 2: Identify the main benefit

   This standardization helps clients understand errors clearly and handle them properly.

3. Final Answer:

   To standardize error messages for better clarity and consistency -> Option A

4. Quick Check:

   Standard error format = clarity [OK]

Hint: Problem Details = clear, consistent error messages [OK]

Common Mistakes:

• Thinking it improves speed
• Confusing with security features
• Assuming it auto-generates docs

2. Which of the following fields is NOT part of the standard Problem Details JSON format?

easy

A. type

B. title

C. timestamp

D. status

Solution

1. Step 1: Recall standard Problem Details fields

   The standard fields include type, title, status, detail, and instance.

2. Step 2: Identify the incorrect field

   Timestamp is not part of the official Problem Details specification.

3. Final Answer:

   timestamp -> Option C

4. Quick Check:

   Standard fields exclude timestamp [OK]

Hint: Remember standard fields: type, title, status, detail, instance [OK]

Common Mistakes:

• Confusing timestamp with instance
• Assuming all error info fields are standard
• Mixing with custom fields

3. Given this Spring Boot controller snippet, what will be the HTTP status code in the Problem Details response when ResourceNotFoundException is thrown?

@RestController
public class MyController {
  @GetMapping("/item/{id}")
  public Item getItem(@PathVariable String id) {
    throw new ResourceNotFoundException("Item not found");
  }
}

medium

A. 404 Not Found

B. 200 OK

C. 500 Internal Server Error

D. 400 Bad Request

Solution

1. Step 1: Understand exception mapping in Spring Boot

   ResourceNotFoundException typically maps to HTTP 404 status to indicate missing resource.

2. Step 2: Confirm standard error status for not found

   Spring Boot's default error handling returns 404 for resource not found exceptions.

3. Final Answer:

   404 Not Found -> Option A

4. Quick Check:

   Resource missing = 404 [OK]

Hint: Resource not found usually means 404 status [OK]

Common Mistakes:

• Assuming 200 OK on exception
• Confusing 400 with 404
• Thinking all exceptions return 500

4. You wrote a custom exception handler to return Problem Details but the API returns a plain error message instead. What is the most likely cause?

medium

A. The exception class does not extend RuntimeException

B. The controller method is not annotated with @GetMapping

C. The application.properties file is missing

D. The handler method is missing @ExceptionHandler annotation

Solution

1. Step 1: Check exception handler setup

   Custom handlers must use @ExceptionHandler to catch exceptions and format responses.

2. Step 2: Identify missing annotation impact

   Without @ExceptionHandler, Spring Boot won't invoke the handler, so default error response is sent.

3. Final Answer:

   The handler method is missing @ExceptionHandler annotation -> Option D

4. Quick Check:

   @ExceptionHandler missing = no custom error [OK]

Hint: Always add @ExceptionHandler to custom error methods [OK]

Common Mistakes:

• Thinking controller mapping affects exception handling
• Assuming properties file controls error format
• Believing exception must extend RuntimeException

5. How can you customize the type field in a Problem Details response for a specific exception in Spring Boot?

hard

A. Override the toString() method of the exception class

B. Create a @ControllerAdvice with @ExceptionHandler and build a ProblemDetail with custom type URI

C. Set a property in application.properties named error.type.custom

D. Add a @RequestMapping with produces = "application/problem+json" on the controller

Solution

1. Step 1: Use @ControllerAdvice and @ExceptionHandler

   To customize error details, define a global handler that catches the exception.

2. Step 2: Build ProblemDetail with custom type URI

   Inside the handler, create a ProblemDetail object and set the type field to a custom URI describing the error.

3. Final Answer:

   Create a @ControllerAdvice with @ExceptionHandler and build a ProblemDetail with custom type URI -> Option B

4. Quick Check:

   Custom type = @ExceptionHandler + ProblemDetail [OK]

Hint: Use @ExceptionHandler to customize ProblemDetail fields [OK]

Common Mistakes:

• Trying to override toString() for error format
• Expecting properties file to set type field
• Using @RequestMapping alone to customize error