Deserializing a Map<String, Object> field with Gson

I have a User object with this structure:
class User {
    private String id;
    private String name;
    private Map<String, Object> properties;

    // GETTERS & SETTERS
}

I have a JSON String with this structure:
{
    "user": {
        "id:"123456789",
        "name:"azerty",
        "emailHash":"123456789", // not used in User class
        "properties": {
            "p1":1,
            "p2":"test",
            "p3":[1, 2, 3, 4],
            "p4":{
               etc...
            }
        }
    }
}

Properties' keys are String, Properties' values can be a String, int, Array, boolean, Map etc.

I try to deserialize this JSON string with Gson like that:
JsonParser parser = new JsonParser();
JsonElement element = parser.parse(jsonString);
JsonObject object = element.getAsJsonObject();

GsonBuilder builder = new GsonBuilder();
builder.setFieldNamingPolicy(FieldNamingPolicy.LOWER_CASE_WITH_UNDERSCORES);
Gson gson = builder.create();
User user = (User) gson.fromJson(object.get("user"), new TypeToken<User>() {}.getType());

Fields 'id' and 'name' are correctly injected but the field 'properties' stays null.

Do you know what I'm doing wrong? Thanks in advance for your help!

java json gson

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edited Jan 11 '13 at 8:21

asked Jan 10 '13 at 16:53

 
Franck Yapadesouci Anso
153110
 
 
 

      
 
I would suggest having properties as JsonObject and then converting the JSON directly to Map<String,Object>. – Srinivas Jan 10 '13 at 16:58
 

      
 
Your code works perfectly fine with one small problem: you seem to have created a GsonBuilder named builder but are then using one named gsonBuilder. If that's actually compiling then you have another GsonBuilder you previously created and are using it by mistake. Other than that ... it deserializes fine on my machine. – Brian Roach Jan 11 '13 at 3:12 
 

      
 
gsonBuilder is an error when I write the topic. It's builder that I use in my code. I'll edit my topic for correction. The properties field is correctly injected in your test? It's very strange it stays to null for me... – Franck Yapadesouci Anso Jan 11 '13 at 8:20 
 

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For me this code:
public class Main {
    public static void main(String[] args) throws IOException {
    GsonBuilder builder = new GsonBuilder();
    builder.setFieldNamingPolicy(FieldNamingPolicy.LOWER_CASE_WITH_UNDERSCORES);
    Gson gson = builder.create();
    FileInputStream inputStream = new FileInputStream(new File("bobi.json"));
    InputStreamReader reader = new InputStreamReader(inputStream);
    User user = gson.fromJson(reader, User.class);
    System.out.println(user.getName());
    System.out.println(user.getId());
    for (String property : user.getProperties().keySet()) {
        System.out.println("Key: " + property + " value: " + user.getProperties().get(property));
    }
    reader.close();
}

Prints this:
azerty
123456789
Key: p1 value: 1.0
Key: p2 value: test
Key: p3 value: [1.0, 2.0, 3.0, 4.0]
Key: p4 value: {}

However, keep in mind that I have stripped the wrapping json object in the file I parse. The file is:
{
        "id":"123456789",
        "name" : "azerty",
        "emailHash":"123456789",
        "properties": {
            "p1":1,
            "p2":"test",
            "p3":[1, 2, 3, 4],
            "p4":{

            }
        }
}

Also I added closing double quote for name and id, which you did not have in your sample.

The User class as requested by the OP. I have added getters and setters for the reason of printing:
import java.util.Map;

class User {
    private String id;
    private String name;
    private Map<String, Object> properties;
    public String getId() {
        return id;
    }
    public void setId(String id) {
        this.id = id;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public Map<String, Object> getProperties() {
        return properties;
    }
    public void setProperties(Map<String, Object> properties) {
        this.properties = properties;
    }
}