解析来自 Wikipedia 的 JSON 响应时遇到问题

Question

所以我正在制作一个搜索 mediawiki api 以获取有关某些名人的简短信息的 Android 应用程序。

这个想法是您可以输入任何名称，它会提供 mediawiki api 关于该名称/人的信息，但现在我只是坚持使用一个名称，直到我弄清楚如何正确解析 JSON。

我需要从这个 json 响应中提取字段： JSON response

这是我目前所拥有的，我认为问题出在 Query 类中，我只是不知道该类需要什么来确保只返回提取字段。当我运行程序时，onResponse() 方法的输出为空。感谢您的帮助。

好的，我做了建议的更改，这是我更新的代码：

;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.TextView;

import com.android.volley.Request;
import com.android.volley.RequestQueue;
import com.android.volley.Response;
import com.android.volley.VolleyError;
import com.android.volley.toolbox.StringRequest;
import com.android.volley.toolbox.Volley;

import com.google.gson.Gson;
import com.google.gson.GsonBuilder;

import java.util.Map;


public class game extends AppCompatActivity {

private static final String ENDPOINT = "https://en.wikipedia.org/w/api.php?    format=json&action=query&prop=extracts&exintro=&explaintext=&titles=Harry%20Potter";

private RequestQueue requestQueue;

private Gson gson;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_game);

    requestQueue = Volley.newRequestQueue(this);

    GsonBuilder gsonBuilder = new GsonBuilder();
    gson = gsonBuilder.create();
}

public void fetchPerson(View view)
{
    fetchPosts();
}
private void fetchPosts() {
    StringRequest request = new StringRequest(Request.Method.GET, ENDPOINT, onPostsLoaded, onPostsError);

    requestQueue.add(request);
}

private final Response.Listener<String> onPostsLoaded = new Response.Listener<String>() {
    @Override
    public void onResponse(String response) {
        final TextView text = (TextView) findViewById(R.id.textView);

        Page page = gson.fromJson(response, Page.class);

        text.setText(page.extract);

    }
};

private final Response.ErrorListener onPostsError = new Response.ErrorListener() {
    @Override
    public void onErrorResponse(VolleyError error) {
        Log.e("PostActivity", error.toString());
    }
};
public class Root {
    String batchcomplete;
    Query  query;
}
public class Query {
    Map<String, Page> pages;
}
public class Page {
    int    pageid;
    int    ns;
    String title;
    String extract;
}

}

Answer 1

我认为问题出在Query 类中

你是对的。

JSON 数据如下所示：

{
  "batchcomplete": "",
  "query": {
    "pages": {
      "23140032": {
        "pageid": 23140032,
        "ns": 0,
        "title": "Frodo Baggins",
        "extract": "Frodo Baggins is a fictional character in J. R. R. Tolkien's legendarium, and the main protagonist of The Lord of the Rings. Frodo is a hobbit of the Shire who inherits the One Ring from his cousin Bilbo Baggins and undertakes the quest to destroy it in the fires of Mount Doom. He is also mentioned in Tolkien's posthumously published works, The Silmarillion and Unfinished Tales."
      }
    }
  }
}

根对象有 2 个字段：batchcomplete 和 query。

您尝试解析为具有以下字段的对象：extract 和 title。

你看到那里的差异吗？

如果你想使用 Gson，你需要所有对象的类。

class Root {
    String batchcomplete;
    Query  query;
}
class Query {
    Map<String, Page> pages;
}
class Page {
    int    pageid;
    int    ns;
    String title;
    String extract;
}

---

更新

您需要将 JSON 解析为 Root 对象。

示例代码：

String json = "{\n" +
              "  \"batchcomplete\": \"\",\n" +
              "  \"query\": {\n" +
              "    \"pages\": {\n" +
              "      \"23140032\": {\n" +
              "        \"pageid\": 23140032,\n" +
              "        \"ns\": 0,\n" +
              "        \"title\": \"Frodo Baggins\",\n" +
              "        \"extract\": \"Frodo Baggins is a fictional character in J. R. R. Tolkien's legendarium, and the main protagonist of The Lord of the Rings. Frodo is a hobbit of the Shire who inherits the One Ring from his cousin Bilbo Baggins and undertakes the quest to destroy it in the fires of Mount Doom. He is also mentioned in Tolkien's posthumously published works, The Silmarillion and Unfinished Tales.\"\n" +
              "      }\n" +
              "    }\n" +
              "  }\n" +
              "}";
Root root = new Gson().fromJson(json, Root.class);
for (Page page : root.query.pages.values()) {
    System.out.println(page.title);
    System.out.println("  " + page.extract);
}

输出

Frodo Baggins
  Frodo Baggins is a fictional character in J. R. R. Tolkien's legendarium, and the main protagonist of The Lord of the Rings. Frodo is a hobbit of the Shire who inherits the One Ring from his cousin Bilbo Baggins and undertakes the quest to destroy it in the fires of Mount Doom. He is also mentioned in Tolkien's posthumously published works, The Silmarillion and Unfinished Tales.