How to parse JSON using GSON in android

Question

I am developing an application where I want to hit the web services and get the data. I am using Google Volley to hit the web service. I am doing it all right but unable to parse JSON using GSON. I am unable to understand where I am doing it wrong.

Here is the URL of Web Services

Here is what I am doing

    RequestQueue requestQueue = Volley.newRequestQueue(this);
    JsonObjectRequest jsonObjectRequest = new JsonObjectRequest(
            Request.Method.GET,
            "https://api.github.com/repos/crashlytics/secureudid/issues",
            null,
            new MyListner(),
            new MyErrorListner()
    );

    requestQueue.add(jsonObjectRequest);

}

class MyListner implements Response.Listener<JSONObject>
{
    @Override
    public void onResponse(JSONObject response) {

        Gson gson = new Gson();
        Results results = gson.fromJson(response.toString(), Results.class);

        for(Test t : results.getmResults())
        {
            Log.e("Tag", t.toString());
        }


    }
}

class MyErrorListner implements Response.ErrorListener
{
    @Override
    public void onErrorResponse(VolleyError error) {
        Log.e("Error", error.getMessage());
    }
}

The other classes are given below

public class Results {


private ArrayList<Test> mResults;

public void setResults(ArrayList<Test> results)
{
    mResults = results;
}

public ArrayList<Test> getmResults()
{
    return mResults;
}
}

public class Test {

@SerializedName("title")
private String mTitle;

@SerializedName("user")
private User mUser;

@SerializedName("created_at")
private String mCreatedAt;

@SerializedName("body")
private String mBody;

@SerializedName("updated_at")
private String mUpdatedAt;

public String getmBody() {
    return mBody;
}

public void setmBody(String mBody) {
    this.mBody = mBody;
}

public String getmUpdatedAt() {
    return mUpdatedAt;
}

public void setmUpdatedAt(String mUpdatedAt) {
    this.mUpdatedAt = mUpdatedAt;
}

public String getmCreatedAt() {
    return mCreatedAt;
}

public void setmCreatedAt(String mCreatedAt) {
    this.mCreatedAt = mCreatedAt;
}

public User getmUser() {
    return mUser;
}

public void setmUser(User mUser) {
    this.mUser = mUser;
}

public String getmTitle() {
    return mTitle;
}

public void setmTitle(String mTitle) {
    this.mTitle = mTitle;
}

@Override
public String toString() {
    return mTitle + " " + mBody + " " + mCreatedAt + " " + mUpdatedAt + " " + mUser.getmLogin() + " ";
}
}


public class User {

@SerializedName("login")
private String mLogin;

public String getmLogin() {
    return mLogin;
}

public void setmLogin(String mLogin) {
    this.mLogin = mLogin;
}
}

Here is the error what I am getting

org.json.JSONException:  Value [{"url":"https:\/\/api.github.com\/repos\/crashlytics\/secureudid\/issues\/28","repository_url":"https:\/\/api.github.com\/repos\/crashlytics\/secureudid","labels_url":"https:\/\/api.github.com\/repos\/crashlytics\/secureudid\/issues\/28\/labels{\/name}","comments_url":"https:\/\/api.github.com\/repos\/crashlytics\/secureudid\/issues\/28\/comments","events_url":"https:\/\/api.github.com\/repos\/crashlytics\/secureudid\/issues\/28\/events","html_url":"https:\/\/github.com\/crashlytics\/secureudid\/pull\/28","id":222258999,"number":28,"title":"Fix broken headings in Markdown files","user":{"login":"bryant1410","id":3905501,"avatar_url":"https:\/\/avatars3.githubusercontent.com\/u\/3905501?v=4","gravatar_id":"","url":"https:\/\/api.github.com\/users\/bryant1410","html_url":"https:\/\/github.com\/bryant1410","followers_url":"https:\/\/api.github.com\/users\/bryant1410\/followers","following_url":"https:\/\/api.github.com\/users\/bryant1410\/following{\/other_user}","gists_url":"https:\/\/api.github.com\/users\/bryant1410\/gists{\/gist_id}","starred_url":"https:\/\/api.github.com\/users\/bryant1410\/starred{\/owner}{\/repo}","subscriptions_url":"https:\/\/api.github.com\/users\/bryant1410\/subscriptions","organizations_url":"https:\/\/api.github.com\/users\/bryant1410\/orgs","repos_url":"https:\/\/api.github.com\/users\/bryant1410\/repos","events_url":"https:\/\/api.github.com\/users\/bryant1410\/events{\/privacy}","received_events_url":"https:\/\/api.github.com\/users\/bryant1410\/received_events","type":"User","site_admin":false},"labels":[],"state":"open","locked":false,"assignee":null,"assignees":[],"milestone":null,"comments":0,"created_at":"2017-04-17T23:26:47Z","updated_at":"2017-04-17T23:26:47Z","closed_at":null,"author_association":"NONE","pull_request":{"url":"https:\/\/api.github.com\/repos\/crashlytics\/secureudid\/pulls\/28","html_url":"https:\/\/github.com\/crashlytics\/secureudid\/pull\/28","diff_url":"https:\/\/github.com\/crashlytics\/secureudid\/pull\/28.diff","patch_url":"https:\/\/github.com\/crashlytics\/secureudid\/pull\/28.patch"},"body":"GitHub changed the way Markdown headings are parsed, so this change fixes it.\n\nSee [bryant1410\/readmesfix](https:\/\/github.com\/bryant1410\/readmesfix) for more information.\n\nTackles bryant1410\/readmesfix#1\n"},{"url":"https:\/\/api.github.com\/repos\/crashlytics\/secureudid\/issues\/13","repository_url":"https:\/\/api.github.com\/repos\/crashlytics\/secureudid","labels_url":"https:\/\/api.github.com\/repos\/crashlytics\/secureudid\/issues\/13\/labels{\/name}","comments_url":"https:\/\/api.github.com\/repos\/crashlytics\/secureudid\/issues\/13\/comments","events_url":"https:\/\/api.github.com\/repos\/crashlytics\/secureudid\/issues\/13\/events","html_url":"https:\/\/github.com\/crashlytics\/secureudid\/issues\/13","id":3923240,"number":13,"title":"Not working with ARC","user":{"login":"SaschaMoellering","id":1321549,"avatar_url":"https:\/\/avatars0.githubusercontent.com\/u\/1321549?v=4","gravatar_id":"","url":"https:\/\/api.github.com\/users\/SaschaMoellering","html_url":"https:\/\/github.com\/SaschaMoellering","followers_url":"https:\/\/api.github.com\/users\/SaschaMoellering\/followers","following_url":"https:\/\/api.github.com\/users\/SaschaMoellering\/following{\/other_user}","gists_url":"https:\/\/api.github.com\/users\/SaschaMoellering\/gists{\/gist_id}","starred_url":"https:\/\/api.github.com\/users\/SaschaMoellering\/starred{\/owner}{\/repo}","subscriptions_url":"https:\/\/api.github.com\/users\/SaschaMoellering\/subscriptions","organizations_url":"https:\/\/api.github.com\/users\/SaschaMoellering\/orgs","repos_url":"https:\/\/api.github.com\/users\/SaschaMoellering\/repos","events_url":"https:\/\/api.github.com\/users\/SaschaMoellering\/events{\/privacy}","received_events_url":"https:\/\/api.github.com\/users\/SaschaMoellering\/received_events","type":"User","site_admin":false},"labels":[],"state":"open","locked":false,"assignee":null,"assignees":[],"milestone":null,"comments":10,"created_at":"20

Your exception's message should have more text than that. Please post the whole thing. — Hovercraft Full Of Eels
– Hovercraft Full Of Eels, Commented Sep 23, 2017 at 15:09
Consider reading the official tutorial on using GSON with Volley instead of parsing then unparsing then parsing the response on the UI thread.... developer.android.com/training/volley/request-custom.html — EpicPandaForce
– EpicPandaForce, Commented Sep 23, 2017 at 18:11

Gaëtan Maisse · Accepted Answer · 2017-09-24 15:09:12Z

1

You are trying to parse an array of object (from your webservices) to an object containing a property mResults which is an array of object (Test);

Instead of using Results class during parsing you need to directly use an ArrayList of Test:

Results results = gson.fromJson(response.toString(), Results.class);

should be

ArrayList<Test> results = gson.fromJson(response.toString(), new TypeToken<ArrayList<Test>>(){}.getType());

As ArrayList is a generic it's not possible to use ArrayList<Test>.class to get a representation of the data type, we must use TypeToken. What is TypeToken?

TypeToken represents a generic type T. Java doesn't yet provide a way to represent generic types, so this class does. Forces clients to create a subclass of this class which enables retrieval the type information even at runtime.

getType returns the type of the class used to build TypeToken and so we can use it in gson fromJson() parsing method.

--

Second problem:

Your are using JsonObjectRequest but server response is a Json array so you need to use JsonArrayRequest and so update MyListner to use JSONArray instead of JSONObject.

BUT

As your are parsing server response manually you can use StringRequest and so avoid parsing step of Volley.

StringRequest jsonObjectRequest = new StringRequest(
    Request.Method.GET,
    "https://api.github.com/repos/crashlytics/secureudid/issues",
    new MyListner(),
    new MyErrorListner()
);

and MyListner is now directly using String:

class MyListner implements Response.Listener<String> {
    @Override
    public void onResponse(String response) {
        Gson gson = new Gson();
        ArrayList<Test> results = gson.fromJson(response, new TypeToken<ArrayList<Test>>() {}.getType());

        for (Test t : results) {
            Log.e("Tag", t.toString());
        }
    }
}

edited Sep 24, 2017 at 15:09

answered Sep 23, 2017 at 16:04

Gaëtan Maisse

12.4k9 gold badges47 silver badges48 bronze badges

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5 Comments

Vaibhav More Over a year ago

Hey, thanks for the answer but still could not solve the error. I think there is problem with results class

Gaëtan Maisse Over a year ago

@AkshayNaik Indeed there was another mistake, I update my answer. It's must be ok now (I try it on a playground project and it's working ;))

Vaibhav More Over a year ago

Maisse Hey, thanks for solution I solved it I just need one more help can you tell me what new TypeToken<Arraylist<Object>>(){}.getType() do in particular

Gaëtan Maisse Over a year ago

@AkshayNaik , answer completed and also updated JsonObjectRequest pb related part. Is it ok ?

Vaibhav More Over a year ago

Yes the answer is complety fine. It worked thanks for the same.

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