Serialization/deserialization library for TOML configuration files. Supports various data types, including nested structures, partial deserialization, and file-based operations. Configurable parsing and serialization options.
Fully Native and Multiplatform Kotlin serialization library for serialization/deserialization of toml format.
Uses native kotlinx.serialization, provided by Kotlin. This library contains no Java code and no Java dependencies.
We believe that TOML is actually the most readable and user-friendly configuration file format.
So we decided to support this format for the kotlinx serialization library.
As this project is needed by the Kotlin community, we need your help.
We will be glad if you will test ktoml or contribute to this project.
In case you don't have much time for this - at least spend 5 seconds to give us a star to attract other contributors!
Thanks! :pray: :partying_face:
Special thanks to those awesome developers who give us great suggestions, help us to maintain and improve this project: @NightEule5, @bishiboosh, @Peanuuutz, @petertrr, @nulls, @Olivki, @edrd-f, @BOOMeranGG, @aSemy, @thomasgalvin
All the code is written in Kotlin common module. This means that it can be built for each and every Kotlin native platform. However, to reduce the scope, ktoml now supports only the following platforms:
js(LEGACY) is not supportedOther platforms could be added later on the demand (just create a corresponding issue) or easily built by users on their machines.
:globe_with_meridians: ktoml supports Kotlin 2.2.0
:heavy_exclamation_mark: Please note, that TOML standard does not define Java-like types: Char, Short, etc.
You can check types that are supported in TOML standard here.
However, in Ktoml, our goal is to comprehensively support all primitive types offered by Kotlin.
General
We are still developing and testing this library, so it has several limitations:
:white_check_mark: deserialization (with some parsing limitations)
:white_check_mark: serialization (with tree-related limitations)
:white_check_mark: Table sections (single and dotted) :white_check_mark: Key-value pairs (single and dotted) :white_check_mark: Long/Integer/Byte/Short types :white_check_mark: Unsigned integer types :white_check_mark: Double/Float types :white_check_mark: Basic Strings :white_check_mark: Literal Strings :white_check_mark: Char type :white_check_mark: Boolean type :white_check_mark: Simple Arrays :white_check_mark: Comments :white_check_mark: Inline Tables :white_check_mark: Offset Date-Time (to of ) :white_check_mark: Local Date-Time (to of ) :white_check_mark: Local Date (to of ) :white_check_mark: Local Time (to of ) :white_check_mark: Multiline Strings :white_check_mark: Arrays (including multiline and nested arrays) :white_check_mark: Maps (for anonymous key-value pairs) :white_check_mark: Nested Inline Tables :white_check_mark: Array of Tables :white_check_mark: Inline Array of Tables :x: Arrays: of Different Types
The library is hosted on the Maven Central.
To import ktoml library you need to add following dependencies to your code:
<dependency>
<groupId>com.akuleshov7</groupId>
<artifactId>ktoml-core</artifactId>
<version>0.7.1</version>
</dependency>
<dependency>
<groupId>com.akuleshov7</groupId>
<artifactId>ktoml-file</artifactId>
<version>0.7.1</version>
</dependency>
implementation 'com.akuleshov7:ktoml-core:0.7.1'
implementation 'com.akuleshov7:ktoml-file:0.7.1'
implementation("com.akuleshov7:ktoml-core:0.7.1")
implementation("com.akuleshov7:ktoml-file:0.7.1")
:heavy_exclamation_mark: as TOML is a foremost language for config files, we have also supported the deserialization from file.
However, we are using okio to read the file, so it will be added as a dependency to your
project if you will import ktoml-file.
Same about okio Source (for example if you need Streaming): ktoml-source.
For basic scenarios of decoding strings you can simply use ktoml-core.
:heavy_exclamation_mark: don't forget to add the serialization plugin kotlin("plugin.serialization") to your project.
Otherwise, @Serialization annotation won't work properly.
Deserialization:
Partial Deserialization can be useful when you would like to deserialize only table and you do not want to reproduce whole object structure in your code.
Serialization:
// add extensions from 'kotlinx' lib to your project:
import kotlinx.serialization.encodeToString
// add com.akuleshov7:ktoml-core to your project:
import com.akuleshov7.ktoml.Toml
@Serializable
data class MyClass(/* your fields */)
val toml = Toml.encodeToString(MyClass(/* ... */))
// add com.akuleshov7:ktoml-file to your project
import com.akuleshov7.ktoml.file.TomlFileWriter
TomlFileWriter.encodeToFile<MyClass>(serializer(), /* file path to toml file */)
Parser to AST:
import com.akuleshov7.ktoml.parsers.TomlParser
import com.akuleshov7.ktoml.TomlConfig
/* ========= */
var tomlAST = TomlParser(TomlInputConfig()).parseStringsToTomlTree(/* list with toml strings */)
tomlAST = TomlParser(TomlInputConfig()).parseString(/* the string that you want to parse */)
tomlAST.prettyPrint()
Ktoml parsing and deserialization was made configurable to fit all the requirements from users. We have created a special configuration class that can be passed to the decoder method:
Toml(
inputConfig = TomlInputConfig(
// allow/prohibit unknown names during the deserialization, default false
ignoreUnknownNames = false,
// allow/prohibit empty values like "a = # comment", default true
allowEmptyValues = true,
// allow/prohibit null values like "a = null", default true
allowNullValues = ,
allowEscapedQuotesInLiteralStrings = ,
allowEmptyToml = ,
ignoreDefaultValues = ,
),
outputConfig = TomlOutputConfig(
indentation = Indentation.FOUR_SPACES,
)
).decodeFromString<MyClass>(
tomlString
)
:heavy_exclamation_mark: You can check how below examples work in decoding ReadMeExampleTest and encoding ReadMeExampleTest.
Ktoml may generate various exceptions when encountering invalid input. It's important to note that certain strict checks
can be enabled or disabled (refer to the Configuration section in this readme). We have intentionally exposed only
two top-level exceptions, namely TomlDecodingException and TomlEncodingException, for public use. You can catch
these exceptions in your code, as all other exceptions inherit from one of these two and will not be publicly accessible.
ktoml is tested against the toml-lang/toml-test suite (TOML 1.0). Known failures are tracked with upstream issues.
See TomlTestBaseline.kt for the full baseline, failure categories, and linked issues.
InstantLocalDateTimeLocalDateLocalTime// add extensions from 'kotlinx' lib to your project:
import kotlinx.serialization.decodeFromString
import kotlinx.serialization.serializer
// add com.akuleshov7:ktoml-core to your project:
import com.akuleshov7.ktoml.deserialize
data class MyClass(/* your fields */)
// to deserialize toml input in a string format (separated by newlines '\n')
// no need to provide serializer() explicitly if you will use extension method from
// <kotlinx.serialization.decodeFromString>
val resultFromString = Toml.decodeFromString<MyClass>(/* string with a toml input */)
val resultFromList = Toml.decodeFromString<MyClass>(serializer(), /* sequence with lines of strings with a toml input */)
// If you need to deserialize only some part of the toml - provide the full name of the toml table.
// The deserializer will work only with this table and it's children.
// For example if you have the following toml, but you want only to decode [c.d.e.f] table:
// [a]
// b = 1
// [c.d.e.f]
// d = "5"
val result = Toml.partiallyDecodeFromString<MyClassOnlyForTable>(serializer(), /* string with a toml input */, "c.d.e.f")
val result = Toml.partiallyDecodeFromString<MyClassOnlyForTable>(serializer(), /* list with toml strings */, "c.d.e.f")
// add com.akuleshov7:ktoml-file to your project
import com.akuleshov7.ktoml.file
val resultFromString = TomlFileReader.decodeFromFile<MyClass>(serializer(), /* file path to toml file */)
val resultFromList = TomlFileReader.partiallyDecodeFromFile<MyClass>(serializer(), /* file path to toml file */, /* table name */)
:heavy_exclamation_mark: toml-file is only one of the example for reading the data from source.
For your particular case you can implement your own source provider based on
okio.Source.
For this purpose we have prepared toml-source module and implemented an
example
with java streams for JVM target.
// add com.akuleshov7:ktoml-source to your project
import com.akuleshov7.ktoml.source
val resultFromString = TomlFileReader.decodeFromSource<MyClass>(serializer(), /* your source */)
val resultFromList = TomlFileReader.partiallyDecodeFromSource<MyClass>(serializer(), /* your source */, /* table name */)
libs.versions.toml)Any existing TOML config is just a TOML file, so ktoml can decode it straight into your own
@Serializable classes — no special support needed. A Gradle version catalog is a good example:
it uses maps of version / library / plugin declarations, [bundles], inline version = { ... }
objects, and the dotted version.ref key.
@Serializable
data class GradleVersionCatalog(
val versions: Map<String, VersionDeclaration> = emptyMap(),
val libraries: Map<String, LibraryDeclaration> = emptyMap(),
val bundles: Map<String, List<String>> = emptyMap(),
val plugins: Map<String, PluginDeclaration> = emptyMap(),
)
// LibraryDeclaration has e.g. `module`, an inline `@SerialName("version")` object,
// and the dotted `@SerialName("version.ref")` key.
val catalog = Toml(inputConfig = TomlInputConfig(ignoreUnknownNames = true))
.decodeFromString<GradleVersionCatalog>(/* contents of libs.versions.toml */)
See GradleVersionCatalogTest
for a complete, runnable example (including the version.ref and inline-table cases).
someBooleanProperty = true
# inline tables in gradle 'libs.versions.toml' notation
gradle-libs-like-property = { id = "org.jetbrains.kotlin.jvm", version.ref = "kotlin" }
[table1]
# null is prohibited by the TOML spec, but allowed in ktoml for nullable types
# so for 'property1' null value is ok. Use: property1 = null
property1 = 100
property2 = 6
[myMap]
a = "b"
c = "d"
[table2]
someNumber = 5
[table2."akuleshov7.com"]
name = 'this is a "literal" string'
# empty lists are also supported
configurationList = ["a", "b", "c"]
# such redeclaration of table2
# is prohibited in toml specification;
# but ktoml is allowing it in non-strict mode:
[table2]
otherNumber = 5.56
# use single quotes
charFromString = 'a'
charFromInteger = 123
can be deserialized to MyClass:
@Serializable
data class MyClass(
val someBooleanProperty: Boolean,
val table1: Table1,
val table2: Table2,
@SerialName("gradle-libs-like-property")
val kotlinJvm: GradlePlugin,
val myMap: Map<String, String>
)
@Serializable
data class Table1(
// nullable property, from toml input you can pass "null"/"nil"/"empty" value (no quotes needed) to this field
val property1: Long?,
// please note, that according to the specification of toml integer values should be represented with Long,
// but we allow to use Int/Short/etc. Just be careful with overflow
val property2: Byte,
// no need to pass this value in the input as it has the default value and so it is NOT REQUIRED
val property3: Short = 5
)
@Serializable
data class Table2(
val someNumber: Long,
@SerialName("akuleshov7.com")
val inlineTable: NestedTable,
val otherNumber: Double,
// Char in a manner of Java/Kotlin is not supported in TOML, because single quotes are used for literal strings.
// However, ktoml supports reading Char from both single-char string and from it's integer code
val charFromString: Char,
val charFromInteger: Char
)
@Serializable
data class NestedTable(
val name: String,
@SerialName("configurationList")
val overriddenName: List<String?>
)
@Serializable
data class GradlePlugin(val id: String, val version: Version)
@Serializable
data class Version(val ref: String)
with the following code:
Toml.decodeFromString<MyClass>(/* your toml string */)
Translation of the example above to json-terminology:
{
"someBooleanProperty": true,
"gradle-libs-like-property": {
"id": "org.jetbrains.kotlin.jvm",
"version": {
"ref": "kotlin"
}
},
"table1": {
"property1": 100,
"property2": 5
},
"table2": {
"someNumber": 5,
"otherNumber": 5.56,
"akuleshov7.com": {
"name": "my name",
"configurationList": [
"a",
"b",
"c"
]
}
}
}
someBooleanProperty = true
# inline tables in gradle 'libs.versions.toml' notation
gradle-libs-like-property = { id = "org.jetbrains.kotlin.jvm", version.ref = "kotlin" }
[table1]
# null is prohibited by the TOML spec, but allowed in ktoml for nullable types
# so for 'property1' null value is ok. Use: property1 = null.
# Null can also be prohibited with 'allowNullValues = false'
property1 = 100
property2 = 6
[table2]
someNumber = 5
[table2."akuleshov7.com"]
name = 'this is a "literal" string'
# empty lists are also supported
configurationList = ["a", "b", "c"]
# such redeclaration of table2
# is prohibited in toml specification;
# but ktoml is allowing it in non-strict mode:
[table2]
otherNumber = 5.56
# use single quotes
charFromString = 'a'
charFromInteger = 123
can be serialized from MyClass:
@Serializable
data class MyClass(
val someBooleanProperty: Boolean,
@TomlComments(
"Comments can be added",
"More comments can also be added"
)
val table1: Table1,
val table2: Table2,
@SerialName("gradle-libs-like-property")
val kotlinJvm: GradlePlugin
)
@Serializable
data class Table1(
@TomlComments(inline = "At the end of lines too")
// nullable values, represented as "null" in toml. For more strict behavior,
// null values can be ignored with the ignoreNullValues config property.
val property1: Long?,
// please note, that according to the specification of toml integer values should be represented with Long
val property2: Long,
// Default values can be ignored with the ignoreDefaultValues config property.
val property3: Long = 5
)
@Serializable
data class Table2(
// Integers can be formatted in hex, binary, etc. Currently only decimal is
// supported.
@TomlInteger(IntegerRepresentation.DECIMAL)
val someNumber: Long,
@SerialName("akuleshov7.com")
@TomlInlineTable // Can be on the property
val inlineTable: InlineTable,
@TomlComments(
"Properties always appear before sub-tables, tables aren't redeclared"
)
val otherNumber: Double
)
@Serializable
data class InlineTable(
@TomlLiteral
val name: String,
@SerialName("configurationList")
val overriddenName: List<String?>
)
@Serializable
@TomlInlineTable // ...or the class
data class GradlePlugin(
val id: String,
// version is "collapsed": single member inline tables become dotted pairs.
val version: Version
)
@Serializable
@TomlInlineTable
data class Version(val ref: String)
with the following code:
Toml.encodeToString<MyClass>(/* your encoded object */)
Certainly. In such cases, you can decode all your key-values into a Map. Even though your schema isn't strictly
defined, you need to provide type-safe structure, for example:
[a]
b = 42
c = "String"
[a.innerTable]
d = 5
[a.otherInnerTable]
d = "String"
If you try to decode it using Toml.decodeFromString<MyClass>(data):
@Serializable
data class MyClass(
val a: Map<String, Map<String, String>>
)
This will result in a TomlDecodingException because types of b and innerTable.d are not a String.
Also, it's possible to have a map of objects:
[coins.bitcoin]
scale = 8
default_volume = 0.1
skip_in_orderbook = 0.00001
[coins.ethereum]
scale = 8
default_volume = 0.2
skip_in_orderbook = 0.00001
[coins.tether]
scale = 2
default_volume = 100.0
skip_in_orderbook = 0.0001
You can decode this structure using Toml.decodeFromString<CoinsConfiguration>(data) where:
@Serializable
data class Coin(
val scale: Long,
@SerialName("default_volume")
val defaultVolume: Double,
@SerialName("skip_in_orderbook")
val skipInOrderbook: Double,
)
@Serializable
data class CoinsConfiguration(
val coins: Map<String, Coin>
)
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