1. Prepare

If your project uses kotlin, you can use the Fastjson-Kotlin module, and use the characteristics of kotlin.

1.1 Download

Maven:

<dependency>
    <groupId>com.alibaba.fastjson2</groupId>
    <artifactId>fastjson2-kotlin</artifactId>
    <version>2.0.57</version>
</dependency>

Add standard library(kotlin-stdlib) and reflection library(kotlin-reflect) as appropriate. If the data class is used or the parameters are passed in through constructor, then add reflection library.

<dependency>
    <groupId>org.jetbrains.kotlin</groupId>
    <artifactId>kotlin-stdlib</artifactId>
    <version>${kotlin-version}</version>
</dependency>

<dependency>
    <groupId>org.jetbrains.kotlin</groupId>
    <artifactId>kotlin-reflect</artifactId>
    <version>${kotlin-version}</version>
</dependency>

• Kotlin Gradle:

dependencies {
    implementation("com.alibaba.fastjson2:fastjson2-kotlin:2.0.57")
}

dependencies {
    implementation("org.jetbrains.kotlin:kotlin-stdlib:$kotlin_version")
    implementation("org.jetbrains.kotlin:kotlin-reflect:$kotlin_version")
}

1.2 Import functions

Whenever the function in the Fastjson-Kotlin, you need to complete the import functions work, otherwise it will be prompted that the corresponding function will not be found.

E.g:

import com.alibaba.fastjson2.to
import com.alibaba.fastjson2.into

If you use a lot of functions, you can use batch import.

import com.alibaba.fastjson2.*

2. Usage

We have unified function names to and into.

• Use to to use ::class.java, suitable for categories without generic Class.
• Use into to use the TypeReference, which is suitable for genetic Class.

First define a User class

class User(
    var id: Int,
    var name: String
)

2.1 Parse JSON into JSONObject

val text = "..." // String
val data = text.parseObject()

val bytes = ... // ByteArray
val data = bytes.parseObject() // JSONObject

2.2 Parse JSON into JSONArray

Kotlin:

val text = "..." // String
val data = text.parseArray() // JSONArray

2.2 Create the Typereference of specified Class

val refer = reference<User>()

2.3 Parse JSON into an Object

No generic:

val text = "..." // String
val data = text.to<User>() // User

Including generic:

val text = "..." // String
val data = text.into<List<User>>() // List<User>
val data = text.into<Map<String, User>>() // Map<String, User>

2.4 Serialization Object to JSON

Serialization as a string:

val data = "..." // Any
val text = data.toJSONString() // String

Serialization as a ByteArray:

val data = "..." // Any
val bytes = data.toJSONByteArray() // ByteArray

2.5 Use JSONObject、JSONArray

2.5.1 Get simple property

val text = "..."
val data = JSON.parseObject(text) // JSONObject

val id = data.getIntValue("id") // Int
val name = data.getString("name") // String

2.5.2 Get Bean Object

No generic:

val obj = ... // JSONObject
val array = ... // JSONArray

val user = array.to<User>(0)
val user = obj.to<User>("key")

Including generic:

val obj = ... // JSONObject
val array = ... // JSONArray

val user = array.into<List<User>>(0)
val user = obj.into<List<User>>("key")

2.5.3 Convert to Bean Object

No generic:

val obj = ... // JSONObject
val array = ... // JSONArray

val user = obj.to<User>() // User
val users = array.toList<User>() // List<User>

Including generic:

val obj = ... // JSONObject
val array = ... // JSONArray

val user = obj.into<HashMap<String, User>>() // HashMap<String, User>
val users = array.into<ArrayList<User>>() // ArrayList<User>

2.5 Convert URL、InputStream to Bean Object

No generic:

val url = ... // URL
val data = url.to<User>()

val input = ... // InputStream
val data = input.to<User>()

Including generic:

val url = ... // URL
val data = url.into<List<User>>()

val input = ... // InputStream
val data = input.into<List<User>>()

3. Advanced usage

3.1 Use JSONPath

3.1.1 Use JSONPath to read specified data

val text = "..."
val path = "$.id".toPath() // JSONPath

val parser = JSONReader.of(text)
val result = path.extract(parser)