如果一个 api 返回 null 值，则调用另一个 api

Question

我正在构建一个用于销售图书的 Android 应用。我有一个集成的条形码扫描仪，我的用户可以使用它扫描他们想要出售的图书的条形码。

我可以使用 Zxing 图书馆从条形码中获取图书的 ISBN 号。我正在使用这个 ISBN 号从 openlibrary.org API 获取数据。

现在的问题是，如果 openlibrary 没有该图书数据，我想调用 Google Books API。

尽管 openlibrary 的数据不如 Google 多，但我仍然使用它们的原因是它们提供了高质量的书籍封面图片。 Google 没有可用的数据。

所以现在我需要知道如果 openlibrary 的响应为空，如何调用 Google 的 API。

这是我的完整代码：

package com.example.gaayathri.barcodetest;

import android.app.Activity;
import android.content.Intent;
import android.os.AsyncTask;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.ImageView;
import android.widget.TextView;
import android.widget.Toast;

import com.bumptech.glide.Glide;
import com.bumptech.glide.request.RequestOptions;
import com.google.zxing.integration.android.IntentIntegrator;
import com.google.zxing.integration.android.IntentResult;

import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;

import java.io.IOException;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;
import java.net.URLConnection;

import okhttp3.Call;
import okhttp3.Callback;
import okhttp3.OkHttpClient;
import okhttp3.Request;
import okhttp3.Response;


public class MainActivity extends AppCompatActivity {

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

        Button button = this.findViewById(R.id.button);
        final Activity activity = this;
        button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                ImageView ivBookImage = findViewById(R.id.ivBookImage);
                ivBookImage.setImageBitmap(null);

                TextView tvTitle = findViewById(R.id.tvTitle);
                tvTitle.setText("");

                TextView tvAuthor = findViewById(R.id.tvAuthor);
                tvAuthor.setText("");


                IntentIntegrator integrator = new IntentIntegrator(MainActivity.this);
                integrator.setPrompt("Scan a barcode");
                integrator.setCameraId(0);  // Use a specific camera of the device
                integrator.setOrientationLocked(true);
                integrator.setBeepEnabled(true);
                integrator.setCaptureActivity(CaptureActivityPortrait.class);
                integrator.initiateScan();
            }
        });

    }

    @Override
    protected void onActivityResult(int requestCode, int resultCode, Intent data) {
        IntentResult result = IntentIntegrator.parseActivityResult(requestCode, resultCode, data);
        if(result != null) {
            if(result.getContents() == null) {
                Log.d("MainActivity", "Cancelled scan");
                Toast.makeText(this, "Cancelled", Toast.LENGTH_LONG).show();
            } else {
                Log.d("MainActivity", "Scanned");
                Toast.makeText(this, "Scanned: " + result.getContents(), Toast.LENGTH_LONG).show();

                final String isbn = result.getContents();

                String bookOpenApi = "https://openlibrary.org/api/books?bibkeys=ISBN:" + isbn + "&jscmd=data&format=json";

                //String bookSearchString = "https://www.googleapis.com/books/v1/volumes?q=isbn:" + isbn;

                OkHttpClient client = new OkHttpClient();

                Request request = new Request.Builder()
                        .url(bookOpenApi)
                        .build();

                client.newCall(request).enqueue(new Callback() {
                    @Override
                    public void onFailure(Call call, IOException e) {

                    }

                    @Override
                    public void onResponse(Call call, final Response response) throws IOException {
                        // ... check for failure using `isSuccessful` before proceeding

                        // Read data on the worker thread
                        final String responseData = response.body().string();

                        // Run view-related code back on the main thread
                        MainActivity.this.runOnUiThread(new Runnable() {
                            @Override
                            public void run() {

                                JSONObject resultObject = null;

                                try {

                                    resultObject = new JSONObject(responseData);

                                    JSONObject isbnObject = resultObject.getJSONObject("ISBN:" + isbn);

                                    String TitleL = isbnObject.getString("title");

                                    if (TitleL.length()!=0){

                                        Toast.makeText(MainActivity.this, "Title length = " + TitleL.length(), Toast.LENGTH_SHORT).show();

                                        try{
                                            TextView tvTitle = findViewById(R.id.tvTitle);
                                            tvTitle.setText("TITLE: "+isbnObject.getString("title"));
                                        }
                                        catch(JSONException jse){
                                            TextView tvTitle = findViewById(R.id.tvTitle);
                                            tvTitle.setText("");
                                            jse.printStackTrace();
                                        }

                                        try{

                                            JSONArray authors = isbnObject.getJSONArray("authors");
                                            JSONObject author = authors.getJSONObject(0);

                                            String authorName = author.getString("name");

                                            TextView tvAuthor = findViewById(R.id.tvAuthor);
                                            tvAuthor.setText("AUTHOR(S): "+ authorName);
                                        }
                                        catch(JSONException jse){
                                            TextView tvAuthor = findViewById(R.id.tvAuthor);
                                            tvAuthor.setText("");
                                            jse.printStackTrace();
                                        }

                                        try{

                                            JSONObject imageObject = isbnObject.getJSONObject("cover");

                                            String imageUrl = imageObject.getString("large");

                                            ImageView ivBookImage = findViewById(R.id.ivBookImage);

                                            Glide.with(MainActivity.this).load(imageUrl).into(ivBookImage);
                                        }
                                        catch(JSONException jse){

                                            Toast.makeText(MainActivity.this, "No book image available", Toast.LENGTH_SHORT).show();
                                            jse.printStackTrace();
                                        }

                                    } else {

                                        String bookSearchString = "https://www.googleapis.com/books/v1/volumes?q=isbn:" + isbn;

                                        OkHttpClient client = new OkHttpClient();

                                        Request request = new Request.Builder()
                                                .url(bookSearchString)
                                                .build();

                                        client.newCall(request).enqueue(new Callback() {
                                            @Override
                                            public void onFailure(Call call, IOException e) {

                                            }

                                            @Override
                                            public void onResponse(Call call, Response response) throws IOException {

                                                final String googleResponseData = response.body().string();

                                                MainActivity.this.runOnUiThread(new Runnable() {
                                                    @Override
                                                    public void run() {

                                                        JSONObject resultObject = null;

                                                        try {

                                                            resultObject = new JSONObject(googleResponseData);

                                                            JSONArray items = resultObject.getJSONArray("items");

                                                            JSONObject volumeInfo = items.getJSONObject(0);

                                                            JSONObject volumeObject = volumeInfo.getJSONObject("volumeInfo");

                                                            String TitleL = volumeObject.getString("title");

                                                            TextView tvTitle = findViewById(R.id.tvTitle);

                                                            tvTitle.setText(TitleL);

                                                        } catch (JSONException e) {
                                                            e.printStackTrace();
                                                        }

                                                        try {

                                                            JSONArray items = resultObject.getJSONArray("items");

                                                            JSONObject volumeInfo = items.getJSONObject(0);

                                                            JSONObject volumeObject = volumeInfo.getJSONObject("volumeInfo");

                                                            JSONArray authorsArray = volumeObject.getJSONArray("authors");

                                                            String authorName = authorsArray.getString(0);

                                                            TextView tvAuthor = findViewById(R.id.tvAuthor);
                                                            tvAuthor.setText("AUTHOR(S): "+ authorName);


                                                        } catch (JSONException e) {
                                                            e.printStackTrace();
                                                        }

                                                    }
                                                });

                                            }
                                        });

                                    }

                                } catch (JSONException e) {
                                    e.printStackTrace();
                                }

                            }
                        });
                    }
                });

            }
        } else {
            // This is important, otherwise the result will not be passed to the fragment
            super.onActivityResult(requestCode, resultCode, data);
        }
    }


}

Answer 1

好的，我通过使用EditText 字段作为关键字段解决了这个问题。所以想法是使用条形码扫描仪返回的 ISBN 号调用openlibrary API，并填充Simple drawee view、Title Edittext 和Author Edittext。

然后检查Title Edittext 字段是否已填充。如果已填充，则表示OpenLibrary API 已返回有效数据。如果Title Edittext 为空，则调用Google's books API。

OnActivityResult()函数的完整源代码如下所示：

@Override
public void onActivityResult(int requestCode, int resultCode, Intent data) {

    final IntentResult result = IntentIntegrator.parseActivityResult(requestCode, resultCode, data);
    if(result != null) {
        if(result.getContents() == null) {
            Log.d("MainActivity", "Cancelled scan");
            Toast.makeText(this, "Cancelled", Toast.LENGTH_LONG).show();
        } else {
            Log.d("MainActivity", "Scanned");
            Toast.makeText(this, "Scanned: " + result.getContents(), Toast.LENGTH_LONG).show();

            runOnUiThread(new Runnable() {
                @Override
                public void run() {
                    // This function will fetch the data from openlibrary API
                    checkinOpenLibrary(result.getContents());

                    EditText tvTitle = findViewById(R.id.etMaterialTitle);
                    if (tvTitle.getText().length() == 0) {
                        // This function will fetch the data from Google's books API
                        checkinGoogleAPI(result.getContents());
                    }

                }
            });

        }
    } else {
        // This is important, otherwise the result will not be passed to the fragment
        super.onActivityResult(requestCode, resultCode, data);
    }