What is System.Text.Json?

System.Text.Json is the high-performance, built-in JSON library for the .NET platform, offering robust capabilities for efficiently converting data between .NET objects and JavaScript Object Notation (JSON) text. It provides the essential functionality for serializing to and deserializing from JSON, making it a cornerstone for modern .NET applications dealing with data exchange.

At its core, System.Text.Json excels at two primary operations:

Understanding Serialization and Deserialization

Serialization: This is the process of converting a .NET object (like a C# class instance) into a JSON string. As the reference explains, serialization is "the process of converting the state of an object, that is, the values of its properties, into a form that can be stored or transmitted."
- Example: Imagine you have a Product object in C# with properties like Id, Name, and Price. System.Text.Json can transform this object into a JSON string such as {"Id": 123, "Name": "Wireless Mouse", "Price": 25.99}. This JSON string can then be sent over a network, stored in a file, or logged.
Deserialization: This is the reverse process, where a JSON string is parsed and converted back into a .NET object.
- Example: If your application receives the JSON string {"Id": 456, "Name": "Mechanical Keyboard", "Price": 120.00}, System.Text.Json can take this string and construct a Product object in your C# code, populating its properties with the values found in the JSON.

Key Features and Advantages

System.Text.Json was introduced with .NET Core 3.0 as a modern alternative to existing JSON libraries, focusing on performance, security, and standards compliance.

Exceptional Performance: Designed for speed and memory efficiency, it often outperforms other JSON libraries, especially in high-throughput scenarios.
Integrated into .NET: Being part of the .NET framework, it requires no external dependencies for basic usage, simplifying project setup and deployment.
Security by Default: Emphasizes secure practices, such as strict adherence to JSON standards and sensible default behaviors to prevent common vulnerabilities.
Standards Compliance: Fully compliant with the JSON specification, ensuring interoperability across different systems and platforms.
Flexible API: Offers various ways to work with JSON:
- JsonSerializer: For straightforward object-to-JSON and JSON-to-object conversions.
- JsonDocument: Provides a read-only Document Object Model (DOM) for efficient, partial access to JSON data without deserializing the entire structure.
- Utf8JsonReader and Utf8JsonWriter: High-performance, forward-only readers and writers for advanced, low-level JSON manipulation.
Asynchronous Support: Optimized for modern asynchronous programming patterns (async/await), crucial for non-blocking I/O operations in web applications.
Customization: Supports custom converters for handling complex types, specific serialization logic, or types not directly supported by default.

When to Use System.Text.Json

System.Text.Json is the recommended default for most new .NET applications requiring JSON processing due to its performance and integration. Common use cases include:

Web APIs (ASP.NET Core): It's the default JSON serializer for ASP.NET Core applications, handling the automatic conversion of request bodies to .NET objects and .NET objects to JSON responses.
Configuration Files: Reading and writing application configurations stored in JSON format.
Inter-Service Communication: Exchanging data between microservices or other distributed systems.
Client-Server Data Transfer: Facilitating data communication between a .NET backend and a JavaScript-based frontend.
Data Persistence: Storing application data in JSON files or databases that support JSON columns.

Core Components and Their Roles

Component	Primary Use
`JsonSerializer`	The simplest and most common entry point for serializing .NET objects to JSON strings or streams, and deserializing JSON strings or streams back into .NET objects. Ideal for scenarios where you want to convert an entire object graph.
`JsonDocument`	Provides a read-only, in-memory representation of a JSON document. Useful when you need to parse a JSON payload and access specific elements without knowing the full schema or deserializing the entire document into an object. It's more memory efficient for partial access than full deserialization.
`Utf8JsonReader`	A low-level, forward-only reader that can parse UTF-8 encoded JSON. It's highly performant and allocation-efficient, suitable for scenarios requiring maximum control over the parsing process or when dealing with very large JSON payloads that can't fit entirely into memory.
`Utf8JsonWriter`	A low-level, forward-only writer that generates UTF-8 encoded JSON. It offers precise control over JSON output and is highly efficient, making it ideal for creating JSON directly, especially in performance-critical applications or when constructing complex JSON structures programmatically.

For more detailed information and code examples, refer to the official Microsoft documentation for System.Text.Json.