https://www.runoob.com/kotlin/kotlin-tutorial.html Kotlin serialization是由kotlin官方提供,可将kotlin对象序列化和反序列化的插件,支持序列化格式包括:JSON, Protobuf, CBOR, Hocon 和Properties serialization使用非常简单: //序列化 val data = Project("kotlinx.serialization", "Kotlin") val json = Json.encodeToString(data) //反序列化 val obj = Json.decodeFromString<Project>(json) 一、添加serialization依赖 在module build.gradle里添加 plugins { id 'kotlin-android' id 'kotlinx-serialization' id 'kotlin-kapt' } dependencies { implementation "org.jetbrains.kotlinx:kotlinx-serialization-json:1.3.0" } 在project build.gradle里添加 buildscript { ext.kotlin_version = '1.5.31' repositories { mavenCentral() } dependencies { classpath "org.jetbrains.kotlin:kotlin-serialization:$kotlin_version" } } 二、Kotlin 序列化指南 1、序列化操作 @Serializable class Project(val name: String, val language: String) fun main() { val data = Project("kotlinx.serialization", "Kotlin") println(Json.encodeToString(data)) } 1、可以被序列化的字段 只有具有支持字段的类的属性会被序列化,因此具有 getter/setter 且没有支持字段和委托属性的属性不会被序列化,如下例所示。 @Serializable class Project( // name带有支持字段属性,可以被序列化 var name: String ) { var stars: Int = 0 // 带有支持字段属性,可以被序列化 val path: String //未带字段,不会被序列化 get() = "kotlin/$name" var id by ::name //代理属性,不会被序列化 } fun main() { val data = Project("kotlinx.serialization").apply { stars = 9000 } println(Json.encodeToString(data)) } //print:{"name":"kotlinx.serialization","stars":9000} 2、默认值操作 默认情况下,默认值不会参与编码: @Serializable data class Project(val name: String, val language: String = "Kotlin") fun main() { val data = Project("kotlinx.serialization") println(Json.encodeToString(data)) } //print:{"name":"kotlinx.serialization"} 如果需要默认值参与序列化,可设置encodeDefaults属性: @Serializable class Project( val name: String, val language: String = "Kotlin", val website: String? = null) fun main() { val data = Project("kotlinx.serialization") println(Json { encodeDefaults = true }.encodeToString(data)) } //print:{"name":"kotlinx.serialization","language":"Kotlin","website":null} 如果不希望null参与序列化,explicitNulls可设置为false 3、强制安全类型 serialization执行Kotlin语言的类型安全,如果json里面有null,而对应属性没有标记为可空,则会报异常 @Serializable data class Project(val name: String, val language: String = "Kotlin") fun main() { val data = Json.decodeFromString<Project>(""" {"name":"kotlinx.serialization","language":null}""") println(data) } 报错:Unexpected JSON token at offset 52: Expected string literal but 'null' literal was found. Use 'coerceInputValues = true' in 'Json {}` builder to coerce nulls to default values. 如果希望json为null时,使用默认值,则设置coerceInputValues = true @Serializable data class Project(val name: String, val language: String = "Kotlin") fun main() { val data = Json { coerceInputValues = true }.decodeFromString<Project>(""" {"name":"kotlinx.serialization","language":null} """) println(data) } //print:Project(name=kotlinx.serialization, language=Kotlin) 4、序列字段名称 默认情况下,编码表示中使用的属性名称(在我们的示例中为 JSON)与它们在源代码中的名称相同。用于序列化的名称称为序列名称,可以使用@SerialName注释进行更改 @Serializable class Project(val name: String, @SerialName("lang") val language: String) fun main() { val data = Project("kotlinx.serialization", "Kotlin") println(Json.encodeToString(data)) } //print:{"name":"kotlinx.serialization","lang":"Kotlin"} 2、反序列化操作 @Serializable class Project(val name: String, val language: String) fun main() { val data = Project("kotlinx.serialization", "Kotlin") println(Json.encodeToString(data)) } 1、可选属性 只有在序列中存在对象的所有属性时,才能反序列化对象。例如: @Serializable data class Project(val name: String, val language: String) fun main() { val data = Json.decodeFromString<Project>("""{"name":"kotlinx.serialization"}""") println(data) } 由于json中没有language属性,会报异常:Exception in thread "main" kotlinx.serialization.MissingFieldException: Field 'language' is required for type with serial name 'example.exampleClasses04.Project', but it was missing 可以通过向属性添加默认值来修复此问题,如: @Serializable data class Project(val name: String, val language: String = "Kotlin") fun main() { val data = Json.decodeFromString<Project>("""{"name":"kotlinx.serialization"}""") println(data) } //print:Project(name=kotlinx.serialization, language=Kotlin) 2、必需属性 在反序列化,如果你希望json必需包含指定的属性名,可以使用@Required注解 @Serializable data class Project(val name: String, @Required val language: String = "Kotlin") fun main() { val data = Json.decodeFromString<Project>(""" {"name":"kotlinx.serialization"} """) println(data) } 例子中,由于json未包含被标记为@Required的language属性,会报异常Field 'language' is required for type with serial name 'example.exampleClasses07.Project', but it was missing 3、JSON属性设置 Json { prettyPrint = true //json格式化 isLenient = true //宽松解析,json格式异常也可解析,如:{name:"小红",age:"18"} + Person(val name:String,val age:Int) ->Person("小红",18) ignoreUnknownKeys = true //忽略未知键,如{"name":"小红","age":"18"} ->Person(val name:String) coerceInputValues = true //强制输入值,如果json属性与对象格式不符,则使用对象默认值,如:{"name":"小红","age":null} + Person(val name:String = "小绿",val age:Int = 18) ->Person("小红",18) encodeDefaults = true //编码默认值,默认情况下,默认值的属性不会参与序列化,通过设置encodeDefaults = true,可让默认属性参与序列化(可参考上述例子) explicitNulls = true //序列化时是否忽略null allowStructuredMapKeys = true //允许结构化映射(map的key可以使用对象) allowSpecialFloatingPointValues = true //特殊浮点值:允许Double为NaN或无穷大 } 1、格式化 @Serializable data class Person(val name:String,val age:Int) val json = Json { prettyPrint = true //是否格式化,默认false prettyPrintIndent = " " //除首行外各行缩进,默认四个空格 } println(json.encodeToString(Person("小明",18))) //print: { "name": "小明", "age": 18 } 2、宽松解析 val json = "{name:小明,age:\"18\"}" //这是一条格式有问题的json val person = Json { isLenient = true //json格式有问题,也有可能解析成功,默认false }.decodeFromString<Person>(json) println(person) //print:Person(name=小明, age=18) 3、忽略未知键 默认情况下,json和实例化对像键值需要一一对应,但实际案例中,json和对象参数名可能无法一一对应,这种情况可以忽略未使用的键 @Serializable data class Person(val name:String) val json = """{"name":"小明","age":18}""" println(Json{ ignoreUnknownKeys = true }.decodeFromString<Person>(json)) //print:Person(name=小明) 4、强制输入值 json的值类型和实例化对象类型不一致时,使用对象的默认值 @Serializable data class Person(val name:String = "小明",val age:Int = 18) val json = """{"name":"小红","age":null}""" println(Json{ coerceInputValues = true //默认false }.decodeFromString<Person>(json)) //print:Person(name=小红, age=18) 5、编码默认值 序列化时,对象默认值参与序列化 @Serializable data class Person(val name:String = "小明",val age:Int = 18) println(Json{ encodeDefaults = false }.encodeToString(Person(name = "小红"))) //plint:{"name":"小红"} println(Json{ encodeDefaults = true }.encodeToString(Person(name = "小红"))) //plint:{"name":"小红","age":18} 6、序列化时忽略null @Serializable data class Person(val name:String = "小明",val age:Int? = null) println(Json{ encodeDefaults = true explicitNulls = false }.encodeToString(Person(name = "小红",age = null))) //print:{"name":"小红"} //explicitNulls = true时,值为null也会参与序列化 println(Json{ encodeDefaults = true explicitNulls = true }.encodeToString(Person(name = "小红",age = null)))kotlin serialization 使用指南