How to serialize an Object to Map by Moshi

Question

I want to serialize an Object to Map by Moshi.Here is my codes by Gson

    public static Map<String, String> toMap(Object obj, Gson gson) {
    if (gson == null) {
        gson = new Gson();
    }
    String json = gson.toJson(obj);
    Map<String, String> map = gson.fromJson(json, new TypeToken<Map<String, String>>() {
    }.getType());
    return map;
}

And how to write by Moshi ?

See https://stackoverflow.com/questions/47114344/moshi-in-android-kotlin-enum-as-mutablemap-key-being-converted-to-string-when/47114650#47114650 — Erlang Parasu, Jun 30 '20 at 21:24

Eric Cochran · Answer 1 · 2017-11-03T17:03:23.330

11

Here's one way. Check out the toJsonValue doc here.

Moshi moshi = new Moshi.Builder().build();

JsonAdapter<Object> adapter = moshi.adapter(Object.class);

Object jsonStructure = adapter.toJsonValue(obj);
Map<String, Object> jsonObject = (Map<String, Object>) jsonStructure;

If you know the type of obj, it'd be better to look up the adapter of that type, rather than of Object. (The Object JsonAdadpter has to look up the runtime type on every toJson call.

edited Nov 03 '17 at 17:03

answered Nov 03 '17 at 16:10

Eric Cochran

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Works fine. I will apply your solution. – Nano Java8 Nov 07 '17 at 01:41
@NanoJava8 you should mark this answer as the correct one. – lagos Aug 05 '21 at 11:41

farhan patel · Answer 2 · 2019-07-31T10:19:05.727

7

@NanoJava8 solution crashes but can be made to work with a minor change using Map instead of HashMap

Type type = Types.newParameterizedType(Map.class, String.class, String.class);

JsonAdapter<Map<String,String>> adapter = moshi.adapter(type);

Map<String,String> map = adapter.fromJson(json);

As stated by Jesse in the answer Moshi support fields as Map but not HashMap.

edited Jul 31 '19 at 10:19

answered Feb 20 '19 at 14:09

farhan patel

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score 3 · Answer 3 · answered Feb 09 '22 at 15:32

In Kotlin:

val type = Types.newParameterizedType(
            MutableMap::class.java,
            String::class.java,
            String::class.java
        )
        val adapter: JsonAdapter<Map<String, String>> = moshi.adapter(type)
        val map: Map<String, String> = adapter.fromJson(responseJson)

score 1 · Answer 4 · answered Nov 02 '17 at 03:07

1

Type type = Types.newParameterizedType(HashMap.class, String.class, String.class);

JsonAdapter<Map<String,String>> adapter = moshi.adapter(type);

Map<String,String> map = adapter.fromJson(json);

answered Nov 02 '17 at 03:07

Nano Java8

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1

Moshi should crash here, preventing you from creating a JsonAdapter for a platform HashMap. If it doesn't, please let me know! – Eric Cochran Nov 02 '17 at 22:14
Yeah, this correctly fails with an IllegalArgumentException. – Eric Cochran Nov 03 '17 at 18:10
It doesn't crash – Nano Java8 Nov 06 '17 at 09:56
@EricCochran It doesn't crash and works as i expect. Version 1.5.0 – Nano Java8 Nov 06 '17 at 10:00
1

Unless you are registering a JsonAdapter for HashMap, you will get: `java.lang.IllegalArgumentException: Platform java.util.HashMap annotated [] requires explicit JsonAdapter to be registered`. Moshi doesn't allow you to hurt yourself by relying on the implementation of platform types. – Eric Cochran Nov 06 '17 at 19:34

score 1 · Answer 5 · answered Apr 27 '20 at 12:36

class HashMapJsonAdapter<K, V>(
  private val keyAdapter: JsonAdapter<K>,
  private val valueAdapter: JsonAdapter<V>
) : JsonAdapter<HashMap<K, V>>() {

  @Throws(IOException::class)
  override fun toJson(writer: JsonWriter, map: HashMap<K, V>?) {
    writer.beginObject()
    for ((key, value) in map ?: emptyMap<K, V>()) {
      if (key == null) {
        throw JsonDataException("Map key is null at ${writer.path}")
      }
    keyAdapter.toJson(writer, key)
    valueAdapter.toJson(writer, value)
    }
    writer.endObject()
  }

  @Throws(IOException::class)
  override fun fromJson(reader: JsonReader): HashMap<K, V>? {
    val result = linkedMapOf<K, V>()
    reader.beginObject()
    while (reader.hasNext()) {
      val name = keyAdapter.fromJson(reader)
      val value = valueAdapter.fromJson(reader)
      val replaced = result.put(name!!, value!!)
      if (replaced != null) {
        throw JsonDataException("Map key '$name' has multiple values at path ${reader.path} : $replaced and value")
      }
    }
    reader.endObject()
    return result
  }

  override fun toString(): String = "JsonAdapter($keyAdapter=$valueAdapter)"

  companion object
}

Any idea how to fix: Caused by: java.lang.IllegalArgumentException: Expected at least one `@ToJson` or `@FromJson` method on ...HashMapJsonAdapter — GuilhE, May 19 '20 at 17:01

How to serialize an Object to Map by Moshi

5 Answers5