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June 29, 2022

Groovy Goodness: Reading TOML Configuration

Since Groovy 4 we can parse TOML configuration data into a Map. Once the TOML data is transformed into the Map we can use all possibilities in Groovy to lookup keys and their values in maps. For example we can use GPath expressions to easily get the value of a (nested) key. To parse TOML configuration data we must use the TomlSlurper class that is in the groovy.toml package. We can use the parse method when we have a file, reader or stream with our configuration. To parse a String value with TOML configuration we use the parseText method.

In the following example we define our configuration using TOML syntax and use the parseText method to transform it into a Map. We use different ways with GPath expressions to read the configuration data:

import groovy.toml.TomlSlurper

// Configuration in TOML syntax.
def config = ''' = "Groovy TOML"
application.version = "1.0.0"
application.ports = [80, 443]

# Set to true for debugging
debug.enabled = false

jdk = 'openjdk version "17.0.3" 2022-04-19'
time = "2022-06-29T07:32:00Z"

name = "dev"
host = "localhost"
port = 8080

name = "uat"
host = "cloud-acc"
port = 80

// We get back a Map with all configuration.
def toml = new TomlSlurper().parseText(config)
// To read data from files, readers or streams we can use overloaded
// versions of the method TomlSlurper#parse.

// We can reference the properties using GPath expressions.
assert == "Groovy TOML"
assert toml.application.version == "1.0.0"
// TOML array is transformed to ArrayList.
assert toml.application.ports == [80, 443]
assert toml.application.ports.class == java.util.ArrayList
assert toml.application == [name: "Groovy TOML", version: "1.0.0", ports: [80, 443]]

// TOML boolean is transformed to boolean.
assert !toml.debug.enabled

assert == /openjdk version "17.0.3" 2022-04-19/
assert == "2022-06-29T07:32:00Z"
// Dates are not parsed, but we get them as String value.
assert == java.lang.String

// Array of tables in TOML are also supported by the TomlSlurper.
assert toml.servers.size() == 2

def developmentConfig = toml.servers.find { s -> == "dev" }
assert == "localhost"
assert developmentConfig.port == 8080

def uatConfig = toml.servers.find { s -> == "uat" }
assert == "cloud-acc"
assert uatConfig.port == 80

assert toml.servers*.name == ["dev", "uat"]

Written with Groovy 4.0.3.