# JSON 序列化概述

The Kotlin serialization library allows you to easily convert Kotlin objects to JSON and back. The [Json](https://kotlinlang.org/api/kotlinx.serialization/kotlinx-serialization-json/kotlinx.serialization.json/-json/) class is the primary tool for this, offering flexibility in how JSON is generated and parsed. You can configure `Json` instances to handle specific JSON behaviors or use its default instance for basic tasks.

With the `Json` class, you can:

* Serialize Kotlin objects to JSON strings using the [encodeToString()](https://kotlinlang.org/api/kotlinx.serialization/kotlinx-serialization-json/kotlinx.serialization.json/-json/encode-to-string.html) function.

* Deserialize JSON strings back to Kotlin objects with the [decodeFromString()](https://kotlinlang.org/api/kotlinx.serialization/kotlinx-serialization-json/kotlinx.serialization.json/-json/decode-from-string.html) function.

* [Work directly with the JsonElement](serialization-json-elements.html) when handling complex JSON structures using the [encodeToJsonElement()](https://kotlinlang.org/api/kotlinx.serialization/kotlinx-serialization-json/kotlinx.serialization.json/encode-to-json-element.html) and the [decodeFromJsonElement()](https://kotlinlang.org/api/kotlinx.serialization/kotlinx-serialization-json/kotlinx.serialization.json/decode-from-json-element.html) functions.

* Use [Experimental](components-stability.html#stability-levels-explained) extension functions to [serialize and deserialize I/O sources](serialization-json-io-sources.html) without creating intermediate strings, including JVM streams as well as [kotlinx-io](https://github.com/Kotlin/kotlinx-io) and [Okio](https://square.github.io/okio/) types.

Before you start, import the following declarations from the serialization library:

```KOTLIN
import kotlinx.serialization.*
import kotlinx.serialization.json.*
```

Here's a simple example that uses the default `Json` instance to show how JSON serialization works in Kotlin:

```KOTLIN
// Imports declarations from the serialization library
import kotlinx.serialization.*
import kotlinx.serialization.json.*

//sampleStart
@Serializable
data class User(val name: String, val age: Int)

fun main() {
    // Uses the default Json instance
    val json = Json

    // Creates a User object
    val user = User("Alice", 30)

    // Converts the User object to a JSON string
    val jsonString = json.encodeToString(user)
    println(jsonString)
    // {"name":"Alice","age":30}

    // Converts the JSON string back to a User object
    val deserializedUser = json.decodeFromString<User>(jsonString)
    println(deserializedUser)
    // User(name=Alice, age=30)
//sampleEnd
}
```

In addition to using the default configuration, you can [customize the Json instance](serialization-json-configuration.html) for specific use cases, such as ignoring unknown keys:

```KOTLIN
// Imports declarations from the serialization library
import kotlinx.serialization.*
import kotlinx.serialization.json.*

//sampleStart
@Serializable
data class Project(val name: String)

// Configures a Json instance to ignore unknown keys
val customJson = Json {
    ignoreUnknownKeys = true
}

fun main() {
    val data = customJson.decodeFromString<Project>("""
        {"name":"kotlinx.serialization","language":"Kotlin"}
    """)
    println(data)
    // Project(name=kotlinx.serialization)
}
//sampleEnd
```

## What's next

* Learn how to [customize Json instances](serialization-json-configuration.html) to address different use cases for serialization and deserialization.

* Explore [advanced JSON element handling](serialization-json-elements.html) to manipulate and work with JSON data before it is parsed or serialized.

* Discover how to [transform JSON during serialization and deserialization](serialization-transform-json.html) for more control over your data.