[Android] Convert Map to JSON using GSON in Kotlin and Java


GSON is a JSON parsing library provided by Google. You can convert Java objects and JSON, but Kotlin can. This time, I could easily convert it with Kotlin's MutableMap, so I would like to share it.

How to use GSON

Write the following in Android Studio.


dependencies {
    implementation 'com.google.code.gson:gson:*.*.*'

"*. *. *" Describe the latest version. Check the latest version from the following. https://github.com/google/gson

After writing the above, click "Sync Now" on Android Studio and you're ready to go.

スクリーンショット 2018-07-03 3.12.37.png

GSON is now available in your project.

JSON conversion of Java Map

I implemented the JSON conversion process as follows.


public void test(){
    ArrayMap<String, String> map = new ArrayMap<>();
    map.put("a1", "A1");
    map.put("a2", "A2");
    map.put("a3", "A3");

    Gson gson = new Gson();
    String jsonString = gson.toJson(map);
    Log.d("Java", jsonString);

    Type type = new TypeToken<ArrayMap<String, String>>(){}.getType();
    ArrayMap<String, String> map2 = gson.fromJson(jsonString, type);
    for (String mapValue : map2.values()) {
        Log.d("Java", mapValue);

When you check the log

D/Java: {"a1":"A1","a2":"A2","a3":"A3"} D/Java: A1   A2   A3

become that way. It was confirmed that JSON conversion is possible. Up to this point, it's been done before, so there's nothing new.

JSON conversion of Kotlin Map

The main subject is from here. Implement the above Java implementation in Kotlin. Map uses Kotlin's MutableMap.


fun test(){
    val map : MutableMap<String, String> = mutableMapOf()
    map.put("a1", "A1")
    map.put("a2", "A2")
    map.put("a3", "A3")

    val gson = Gson()
    val jsonString : String = gson.toJson(map)
    Log.d("Kotlin", jsonString)
    val type : Type = object : TypeToken<MutableMap<String, String>>() {}.type

    val map2 : MutableMap<String, String> = gson.fromJson(jsonString, type)
    for (mapValue in map2.values) {
        Log.d("Kotlin", mapValue)

When you check the log

D/Kotlin: {"a1":"A1","a2":"A2","a3":"A3"} D/Kotlin: A1      A2      A3

become that way. It was confirmed that JSON conversion can be performed in the same way as Java.

At the end

The ease of use of Kotlin is GOOD!

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