json-logic-kotlin

This is a pure Kotlin implementation of JsonLogic http://jsonlogic.com rule engine. JsonLogic is documented extensively at JsonLogic.com, including examples of every supported operation.

This is a fork of the implementation done by Advantage FSE. It includes a few differences to the original:

• JsonLogic.apply returns Any? instead of String. Therefore, you can work with native objects, e.g. a rule might actually return a boolean or numeric value. We also got rid of all unnecessary conversions to and from strings during evaluation.

• If you use custom operators recursively, the order of evaluation is matched to the JavaScript and Python implementations.

• JSON parsing is handled by Jackson instead of GSON.

• The official JsonLogic.com test suite is bundled instead of loaded dynamically, making test runs more reliable.

Installation

Gradle

allprojects {
  repositories {
    maven { url 'https://jitpack.io' }
  }
}

dependencies {
  implementation 'com.github.pretix:json-logic-kotlin:1.0.0'
}

Examples

Typically jsonLogic will be called with a rule object and optionally a data object. Both parameters can either be JSON formatted strings or Any Kotlin objects.

Simple

This is a simple test, equivalent to 1 == 1

JsonLogic().apply("""{"==":[1,1]}""")
//true

Compound

An example with nested rules as strings

val jsonLogic = JsonLogic()
jsonLogic.apply("""
    { "and" : [
        { ">" : [3,1] },
        { "<" : [1,3] }
    ] }
""")
//true

An example with nested rules as objects

val jsonLogic = JsonLogic()
val logic = mapOf(
    "and" to listOf(
        mapOf(">" to listOf(3, 1)),
        mapOf("<" to listOf(1, 3))
    )
)
jsonLogic.apply(logic)
//true

Data-Driven

You can use the var operator to get attributes of the data object

val jsonLogic = JsonLogic()
val rule = mapOf("var" to listOf("a"))
val data = mapOf("a" to 1, "b" to 2)
jsonLogic.apply(rule, data)
//1

or with json string parameters

val jsonLogic = JsonLogic()
jsonLogic.apply(
    """{ "var" : ["a"] }""", // Rule
    "{ a : 1, b : 2 }" // Data
)
//1

You can also use the var operator to access an array by numeric index

JsonLogic().apply(
    """{"var" : 1 }""", // Rule
    """[ "apple", "banana", "carrot" ]""" // Data
)
//banana

Customization

Adding custom operations is also supported.

val jsonLogic = JsonLogic()
jsonLogic.addOperation("sqrt") { l, _ ->
    try {
        if (l != null && l.size > 0) Math.sqrt(l[0].toString().toDouble())
        else null
    } catch (e: Exception) {
        null
    }
}
jsonLogic.apply("""{"sqrt":"9"}""")
//3

An example passing object parameters

val jsonLogic = JsonLogic()
jsonLogic.addOperation("pow") { l, _ ->
    try {
        if (l != null && l.size > 1) Math.pow(l[0].toString().toDouble(), l[1].toString().toDouble())
        else null
    } catch (e: Exception) {
        null
    }
}
jsonLogic.apply(mapOf("pow" to listOf(3,2)))
//9

Compatibility

This implementation is as close as it gets to the JS implementation and passes all the official Unit Tests.