如何在Android中使用GSON解析JSON

Question

我正在開發一個應用程序，我想在該應用程序上訪問Web服務並獲取數據。 我正在使用Google Volley來訪問Web服務。 我做的很好，但是無法使用GSON解析JSON 。 我無法理解我在哪里做錯了。

這是Web服務的URL

這是我在做什么

    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());
    }
}

其他課程如下

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;
}
}

這是我得到的錯誤

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

您正在嘗試將對象數組（來自Web服務）解析為包含屬性mResults的對象，該屬性是對象數組（ Test ）；

代替在解析過程中使用Results類，您需要直接使用Test的ArrayList ：

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

應該

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

由於ArrayList是泛型，因此無法使用 ArrayList<Test>.class來獲取數據類型的表示形式，因此必須使用TypeToken 。 什么是TypeToken？

TypeToken表示通用類型T。Java尚未提供表示通用類型的方法，因此此類可以。 強制客戶端創建此類的子類，即使在運行時也可以檢索類型信息。

getType返回用於構建TypeToken的類的類型，因此我們可以在gson fromJson()解析方法中使用它。

-

第二個問題：

您正在使用JsonObjectRequest但是服務器響應是一個Json數組，因此您需要使用JsonArrayRequest並更新MyListner以使用JSONArray而不是JSONObject 。

但

當您手動解析服務器響應時，可以使用StringRequest ，因此避免了Volley解析步驟。

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

MyListner現在直接使用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());
        }
    }
}