如何在Android中使用GSON解析JSON

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

Answer 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());
        }
    }
}