json_annotation_tools 0.0.1

Transform cryptic JSON parsing errors into crystal-clear, actionable error messages. Debug JSON issues in seconds, not hours. Perfect companion to json_annotation and json_serializable.

JSON Annotation Tools 🛠️

Stop wrestling with cryptic JSON parsing errors! This package provides powerful debugging tools and safe parsing utilities that make JSON deserialization errors crystal clear and easy to fix.

[Error Comparison Demo] Before vs After: See how error messages transform from cryptic to crystal clear

🎯 Why You Need This

Ever seen this frustrating error?

type 'String' is not a subtype of type 'int'

And spent hours figuring out which field in your JSON caused it? Those days are over.

Before vs After

❌ Before (Standard JSON parsing):

// Unclear error: "type 'String' is not a subtype of type 'int'"
// Which field? What value? Who knows! 🤷‍♂️
User.fromJson(json);

✅ After (With JSON Annotation Tools):

// Crystal clear error message:
// "❌ Error parsing key 'age': expected int, but got String. Value: "25""
User.fromJsonSafe(json);

[Complete Demo Flow] 🎬 See the complete debugging experience in action

🚀 Features

• 🔍 Pinpoint Error Location: Know exactly which JSON field caused the parsing error
• 📝 Detailed Error Messages: See the expected type, actual type, and problematic value
• 🛡️ Type Safety: Catch type mismatches before they crash your app
• 🚫 Missing Field Detection: Clear warnings for missing required fields
• 🔄 Seamless Integration: Works perfectly with json_annotation and json_serializable
• ⚡ Zero Performance Impact: Only active during parsing errors

📱 Interactive Demo App

Experience the power of enhanced error messages with our interactive demo app:

[Demo App Home]

Try all features live on Android, iOS, or Web!

What You'll See:

• 🚨 Real Error Comparisons: Before vs after side-by-side
• 🔧 Copy-Paste Solutions: Ready-to-use code fixes
• 🎯 Smart Suggestions: AI-powered field name matching
• 🔍 Advanced Diagnostics: Property mapping analysis
• ⚡ Live Testing: Try different JSON scenarios instantly

📦 Installation

Add to your pubspec.yaml:

dependencies:
  json_annotation_tools: ^0.0.1
  json_annotation: ^4.9.0

🎮 Quick Start

1. Import the package

import 'package:json_annotation_tools/json_annotation_tools.dart';

2. Use in your JSON models

Traditional approach (error-prone):

@JsonSerializable()
class User {
  final int id;
  final String name;
  final int age;
  
  User({required this.id, required this.name, required this.age});
  
  factory User.fromJson(Map<String, dynamic> json) => _$UserFromJson(json);
}

Enhanced approach (bulletproof):

@JsonSerializable()
class User {
  final int id;
  final String name;
  final int age;
  
  User({required this.id, required this.name, required this.age});
  
  // Original method (keep for compatibility)
  factory User.fromJson(Map<String, dynamic> json) => _$UserFromJson(json);
  
  // Enhanced method with detailed error reporting
  factory User.fromJsonSafe(Map<String, dynamic> json) {
    return User(
      id: json.getSafe('id', (v) => v as int),
      name: json.getSafe('name', (v) => v as String),
      age: json.getSafe('age', (v) => v as int),
    );
  }
}

3. Handle problematic JSON gracefully

final problematicJson = {
  'id': 123,
  'name': 'John Doe',
  'age': '25', // Oops! String instead of int
};

try {
  final user = User.fromJsonSafe(problematicJson);
} catch (e) {
  print(e);
  // Output: ❌ Error parsing key 'age': expected int, but got String. Value: "25"
  // Now you know exactly what to fix!
}

🎯 Real-World Examples

API Response Debugging

// When your API suddenly returns unexpected data types
final apiResponse = {
  'user_id': '12345',    // Should be int, but API returned string
  'balance': 'null',     // Should be double, but got string "null"
  'premium': 1,          // Should be bool, but got int
};

// Get clear, actionable error messages:
try {
  final user = User.fromJsonSafe(apiResponse);
} catch (e) {
  // ❌ Error parsing key 'user_id': expected int, but got String. Value: "12345"
  // Now you can immediately contact the backend team with specific details!
}

Nullable Fields Made Easy

factory User.fromJsonSafe(Map<String, dynamic> json) {
  return User(
    id: json.getSafe('id', (v) => v as int),
    name: json.getSafe('name', (v) => v as String),
    age: json.getSafe('age', (v) => v as int),
    // Optional fields with safe parsing
    email: json.getNullableSafe('email', (v) => v as String),
    phoneNumber: json.getNullableSafe('phone', (v) => v as String),
  );
}

Complex Type Parsing

// Parse nested objects and lists safely
factory Order.fromJsonSafe(Map<String, dynamic> json) {  
  return Order(
    id: json.getSafe('id', (v) => v as String),
    items: json.getSafe('items', (v) => 
      (v as List).map((item) => OrderItem.fromJsonSafe(item)).toList()
    ),
    totalAmount: json.getSafe('total', (v) => (v as num).toDouble()),
    createdAt: json.getSafe('created_at', (v) => DateTime.parse(v as String)),
  );
}

🔧 Advanced Usage

Custom Parser Functions

// Create reusable parsers for common patterns
T parseEnum<T>(List<T> values, dynamic value) {
  final stringValue = value as String;
  return values.firstWhere(
    (e) => e.toString().split('.').last == stringValue,
    orElse: () => throw FormatException('Invalid enum value: $stringValue'),
  );
}

// Use in your models
factory UserStatus.fromJsonSafe(Map<String, dynamic> json) {
  return UserStatus(
    status: json.getSafe('status', (v) => parseEnum(StatusType.values, v)),
  );
}

Debugging Production Issues

// Add logging to track parsing issues in production
factory User.fromJsonSafe(Map<String, dynamic> json) {
  try {
    return User(
      id: json.getSafe('id', (v) => v as int),
      name: json.getSafe('name', (v) => v as String),
      age: json.getSafe('age', (v) => v as int),
    );
  } catch (e) {
    // Log the error with full context for debugging
    FirebaseCrashlytics.instance.recordError(
      e, 
      null, 
      fatal: false,
      information: ['JSON: ${jsonEncode(json)}'],
    );
    rethrow;
  }
}

🎨 Best Practices

1. Keep Both Methods: Maintain both fromJson and fromJsonSafe for backward compatibility
2. Use in Development: Use fromJsonSafe during development and testing
3. Production Strategy: Consider using fromJsonSafe in production for critical models
4. Error Handling: Always wrap safe parsing in try-catch blocks
5. Logging: Log parsing errors with full context for debugging

🔗 Works Great With Your Stack

Perfect integration with Dio, Retrofit, and json_annotation - use the same safe parsing methods with your existing API client setup.

🤝 Migration Guide

From Standard JSON Serialization

1. Keep existing code working: Your current fromJson methods continue to work
2. Add safe alternatives: Create fromJsonSafe methods alongside existing ones
3. Test thoroughly: Use fromJsonSafe in tests to catch issues early
4. Gradual adoption: Migrate critical models first, then expand usage

📊 Performance Impact

• Zero overhead during successful parsing
• Minimal impact during errors (only when you need the debugging info)
• Same memory usage as standard parsing
• Compatible with all existing JSON serialization patterns

🐛 Troubleshooting

Common Issues

Q: "I'm getting errors about missing keys"

// Use getNullableSafe for optional fields
email: json.getNullableSafe('email', (v) => v as String),

Q: "How do I handle nested objects?"

// Parse nested objects recursively
address: json.getSafe('address', (v) => Address.fromJsonSafe(v as Map<String, dynamic>)),

Q: "Can I use this with existing json_serializable models?"

// Yes! Add safe methods alongside generated ones
factory User.fromJson(Map<String, dynamic> json) => _$UserFromJson(json); // Generated
factory User.fromJsonSafe(Map<String, dynamic> json) { /* Your safe implementation */ }

🤝 Contributing

We welcome contributions! Please see our Contributing Guide for details.

📄 License

This project is licensed under the MIT License - see the LICENSE file for details.

🙏 Acknowledgments

• Built to complement the excellent json_annotation and json_serializable packages
• Inspired by the need for better JSON debugging in Flutter development
• Thanks to the Flutter community for feedback and suggestions

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Made with ❤️ for the Flutter community

Stop debugging JSON parsing errors in the dark - see exactly what's wrong and fix it fast!