How to convert JSON fields into a JAVA map using GSON

Question

I have a JSON data which looks like this:

{
 "status": "status",
 "date": "01/10/2019",
 "time": "10:30 AM",
 "labels": {
     "field1": "value1",
     "field2": "value2",
     ...
     "field100": "value100"
 }
 "description": "some description"
}

In my Java code, I have two classes:

Alerts class which has the following fields - status, date, time, description and Labels class.
The inner Labels class which is supposed to hold all the fields from field1 through field100 (and more)

I'm parsing this JSON into GSON like this:

Alerts myAlert = gson.fromJson(alertJSON, Alert.class);

The above code parses the JSON into the Alert object and the Labels object.

Question: Instead of mapping the fields (field1, field2, etc) inside Labels object as individual String fields, how can I parse them into a map?

For example, the Labels object would look like this:

public class Labels {

   // I want to parse all the fields (field1, field2, etc) into 
   // this map
   Map<String, String> fields = new HashMap<>(); 

}

How do I do this?

Akceptor · Accepted Answer · 2019-01-10 15:12:50Z

4

Declaring Alert object like this:

public class Alert {
    private String description;
    private String status;
    private Map<String, String> labels;
    ...
}

works for me and this code

Alert myAlert = gson.fromJson(alertJSON, Alert.class);
System.out.println(myAlert.getLabels());

prints the map as {field1=value1, field2=value2, field100=value100}

So that no intermediate object is required

answered Jan 10, 2019 at 15:12

Akceptor

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Comments

sovas · Accepted Answer · 2019-01-10 15:09:44Z

3

You can use TypeToken to directly specify labels.

import java.lang.reflect.Type;
import com.google.gson.reflect.TypeToken;

Type mapType = new TypeToken<Map<String, String>>(){}.getType();
Map<String, String> myMap = gson.fromJson("{'field1':'value1','field2':'value2'}", mapType);

answered Jan 10, 2019 at 15:09

sovas

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Comments

Hellomr · Accepted Answer · 2019-01-10 15:53:01Z

For general cases - some more flexible way: gson can register type adapters:

Gson gson = new GsonBuilder().registerTypeAdapter(Labels.class, new LabelsDeserializer()).create();

And deserializer for your case is:

public class LabelsDeserializer implements JsonDeserializer<Labels>
{
    @Override
    public Labels deserialize(JsonElement jsonElement, Type type, JsonDeserializationContext jsonDeserializationContext) throws JsonParseException
    {
        if (!jsonElement.isJsonNull())
        {
            Labels label = new Labels();
            jsonElement.getAsJsonObject().entrySet().forEach(entry -> label.getFields().put(entry.getKey(), entry.getValue().getAsString()));

            return label;
        }
        else
        {
            return null;
        }
    }
}

For serlializing it's needed to implement JsonSerializer<...>

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