java - AsyncTask 在后台方法 try/catch 中执行，两者都被执行

Question

我正在使用async任务从url获取Json数据。正如你所看到的，在日志 cat 中，我得到了 url 输出，但 catch block 仍然被执行，我无法找出错误

代码:

public class MainActivity extends AppCompatActivity {
    Scanner scanner;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        weatherTask task = new weatherTask();
        task.execute();
    }
    private class weatherTask extends AsyncTask<String,Void,String> {
        @Override
        protected String doInBackground(String... strings) {
            try{
                URL url = new URL("http://api.openweathermap.org/data/2.5/weather?lat=28.732754&lon=77.175051&appid=e6a99aef963a3e835da961d3cf9aeeb6");
                HttpURLConnection urlConnection = (HttpURLConnection) url.openConnection();
                InputStream in = urlConnection.getInputStream();
                scanner = new Scanner(in);
                scanner.useDelimiter("\\A");
                boolean has_input = scanner.hasNext();
                if(has_input){
                    Log.d("url output",scanner.next());
                    String result = scanner.next().toString();
                    return result;
                }
            }
            catch (Exception e){
//                errorText.setVisibility(View.VISIBLE);
                Log.i("inside","do in back");
//                relativeLayout.setVisibility( View.GONE);
                e.printStackTrace();
            }
            return null;
        }
    }
}

日志猫

2020-01-12 20:54:51.814 17593-17663/? D/url output: {"coord":{"lon":77.18,"lat":28.73},"weather":[{"id":711,"main":"Smoke","description":"smoke","icon":"50n"}],"base":"stations","main":{"temp":289.2,"feels_like":288.97,"temp_min":288.15,"temp_max":289.82,"pressure":1014,"humidity":67},"visibility":2200,"wind":{"speed":0.37,"deg":12},"clouds":{"all":20},"dt":1578842444,"sys":{"type":1,"id":9165,"country":"IN","sunrise":1578793526,"sunset":1578831159},"timezone":19800,"id":1269125,"name":"Jawaharnagar","cod":200}
2020-01-12 20:54:51.814 17593-17663/? I/inside: do in back
2020-01-12 20:54:51.814 17593-17663/? W/System.err: java.util.NoSuchElementException
2020-01-12 20:54:51.815 17593-17663/? W/System.err:     at java.util.Scanner.throwFor(Scanner.java:874)
2020-01-12 20:54:51.815 17593-17663/? W/System.err:     at java.util.Scanner.next(Scanner.java:1388)
2020-01-12 20:54:51.815 17593-17663/? W/System.err:     at com.tarandeepsingh.test.MainActivity$weatherTask.doInBackground(MainActivity.java:91)
2020-01-12 20:54:51.815 17593-17663/? W/System.err:     at com.tarandeepsingh.test.MainActivity$weatherTask.doInBackground(MainActivity.java:24)
2020-01-12 20:54:51.815 17593-17663/? W/System.err:     at android.os.AsyncTask$2.call(AsyncTask.java:333)
2020-01-12 20:54:51.815 17593-17663/? W/System.err:     at java.util.concurrent.FutureTask.run(FutureTask.java:266)
2020-01-12 20:54:51.815 17593-17663/? W/System.err:     at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:245)
2020-01-12 20:54:51.815 17593-17663/? W/System.err:     at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1167)
2020-01-12 20:54:51.815 17593-17663/? W/System.err:     at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:641)
2020-01-12 20:54:51.815 17593-17663/? W/System.err:     at java.lang.Thread.run(Thread.java:764)

谢谢

Answer 1

NoSuchElementException 表示没有更多可用 token 。请尝试以下

boolean has_input = scanner.hasNext();

if(has_input) {
    String result = scanner.next();

    Log.d("url output", result);

    return result;
}