JSON GSON.fromJson Java Objects

Question

I am trying to load my Json into my class

public User() {
    this.fbId = 0;
    this.email = "";
    this.name = "";
    this.thumb = "";
    this.gender = "";
    this.location = "";
    this.relationship = null;
    this.friends = new ArrayList();
}

{
    users:{
        user:{
            name:'the name',
            email:'[email protected]',
            friends:{
                user:{
                    name:'another name',
                    email:'[email protected]',
                    friends:{
                        user:{
                            name:'yet another name',
                            email:'[email protected]'
                        }
                    }
                }
            }
        }
    }
}

I am struggling to get GSON to load the user details into the above Java object with the following code

User user = gson.fromJson(this.json, User.class);

That's XML, not JSON, mate. ...okay, you edited your question. Show us the JSON! Also, that's a constructor, not a class. — Matt Ball
– Matt Ball, Commented Mar 15, 2011 at 16:33
right i'm their never had problems like that before lol sorry guys thanks for the quick replies and sorry for messing you about — Deviland
– Deviland, Commented Mar 15, 2011 at 16:37
its the constructor from the class with all the attributes of the class, thought it might be helpful to match the Json with the class in the example :) — Deviland
– Deviland, Commented Mar 15, 2011 at 16:38

BalusC · Accepted Answer · 2011-03-15 16:50:08Z

44

The JSON is invalid. A collection is not to be represented by {}. It stands for an object. A collection/array is to be represented by [] with commaseparated objects.

Here's how the JSON should look like:

{
    users:[{
        name: "name1",
        email: "email1",
        friends:[{
            name: "name2",
            email: "email2",
            friends:[{
                name: "name3",
                email: "email3"
            },
            {
                name: "name4",
                email: "email4"
            }]
        }]
    }]
}

(note that I added one more friend to the deepest nested friend, so that you understand how to specify multiple objects in a collection)

Given this JSON, your wrapper class should look like this:

public class Data {
    private List<User> users;
    // +getters/setters
}

public class User {
    private String name;
    private String email;
    private List<User> friends;
    // +getters/setters
}

and then to convert it, use

Data data = gson.fromJson(this.json, Data.class);

and to get the users, use

List<User> users = data.getUsers();

edited Mar 15, 2011 at 16:50

answered Mar 15, 2011 at 16:44

BalusC

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3 Comments

Deviland Over a year ago

Thanks Balus C you I used a tool to convert my test data from XML to JSON this is a lesson I have to learn don't trust third party sites to do the work I should be doing.

Piscean Over a year ago

Hi everyone used this in solution: gson.fromJson(this.json, User.class); I want to know whats this.json. Is it a json object or what? if it is a hard-coded json object then where should we create that object to access it with this.json?

BalusC Over a year ago

@Piscean: it's just the input JSON string. See also the original question and the Gson manual. If you can't figure it, just press Ask Question button on right top.

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