GsonPointer

Adds JSON Pointer (RFC 6901) support to Google Gson library. Source code is written in Kotlin by literally importing and modifying original fork by John Lombardo.

Usage

This library provides a simple lookup implementation, that tries to always provide a valid Kotlin object for quick and easy dereferencing and direct usage of JSON pointers to read values from Gson's JsonParser when you don't want to keep making specific Kotlin data classes for one off use cases or specific error handling. By using the provided safeX extension properties on JsonElement, you can rest assured that you'll always get a good value back instead of an Exception at runtime.

Parse JSON using Gson

Consider a JSON error response that you're receiving from your API like this:

{
    "email": [
        "Enter a valid email address."
    ]
}

Instead of using Gson().fromJson() we use Gson's JsonParser class to get a JsonElement pointing to the root of the JSON tree, like this:

    import com.google.gson.JsonParser
    import com.traversient.gsonpointer.pointer

    //body is inside a `use` closure from OKHTTP response
    val element = JsonParser().parse(body!!.charStream())
    // element is JsonElement

Access and read value using a JsonPointer

Once you have a JsonElement you can get a JsonPointer with it as root, using the convenient Kotlin extension function provided by this library.

    val pointer = element.pointer
    //pointer is JsonPointer    

Once you have a JsonPointer, you can directly access a JsonPointer anywhere in the whole JSON tree using pointer syntax:

    val message = pointer.at("/email/0").safeString
    //message is the first error String, "Enter a valid email address"

Safe value retreival

The at() function always returns a valid JsonElement, even when there is no match. You can use the standard isJsonPrimitive or other similar methods to determine what you got back. You can more easily use the provided convenience get properties to get either the actual value at the node or a default value that you can check and flow against.

• JsonElement.safeNumber returns any Number found at the pointer, or a 0
• JsonElement.safeString returns any String found at the pointer, or a ""
• JsonElement.safeBoolean returns any Boolean found at the pointer, or a false
• JsonElement.safeJsonObject returns any JsonObject found at the pointer, or a JsonObject(), which works out to an empty JSON object: {}
• JsonElement.safeJsonArray returns any JsonArray found at the pointer, or a JsonArray(), which works out to an empty JSON Array, []

Installation

GsonPointer uses JitPack.io to distribute the library. Add the Jitpack repository to your root project level build.gradle with:

allprojects {
    repositories {
        jcenter()
        maven {
            url "https://jitpack.io"
        }
        google()
    }
}

and to your app gradle:

dependencies {
    implementation 'com.github.dhiraj:gsonpointer:0.2'
}