從URL從.txt文件獲取內容時出錯

Question

URL scoreU = null;
    try {
        scoreU = new URL("http://m.uploadedit.com/b044/1422550899503.txt");
    } catch (MalformedURLException e) {
        e.printStackTrace();
    }
    BufferedReader in = null;
    try {
        in = new BufferedReader(
                new InputStreamReader(
                        scoreU.openStream()));
    } catch (IOException e) {
        e.printStackTrace();
    }

    String inputLine;

    try {
        while ((inputLine = in.readLine()) != null)
            System.out.println(inputLine);
    } catch (IOException e) {
        e.printStackTrace();
    }

    try {
        in.close();
    } catch (IOException e) {
        e.printStackTrace();
    }

那是我的有關從URL獲取文本的代碼。 這是我第一次這樣做，我無法理解我的錯誤。 （我必須用try / catch包圍幾乎所有內容。

錯誤：

 java.lang.RuntimeException: Unable to start activity ComponentInfo{com.wc.gap.worldcupfixture/com.wc.gap.worldcupfixture.MainActivity}: android.os.NetworkOnMainThreadException at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2298) at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360) at android.app.ActivityThread.access$800(ActivityThread.java:144) at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278) at android.os.Handler.dispatchMessage(Handler.java:102) at android.os.Looper.loop(Looper.java:135) at android.app.ActivityThread.main(ActivityThread.java:5221) at java.lang.reflect.Method.invoke(Native Method) at java.lang.reflect.Method.invoke(Method.java:372) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694) Caused by: android.os.NetworkOnMainThreadException at android.os.StrictMode$AndroidBlockGuardPolicy.onNetwork(StrictMode.java:1147) at java.net.InetAddress.lookupHostByName(InetAddress.java:418) at java.net.InetAddress.getAllByNameImpl(InetAddress.java:252) at java.net.InetAddress.getAllByName(InetAddress.java:215) at com.android.okhttp.HostResolver$1.getAllByName(HostResolver.java:29) at com.android.okhttp.internal.http.RouteSelector.resetNextInetSocketAddress(RouteSelector.java:232) at com.android.okhttp.internal.http.RouteSelector.next(RouteSelector.java:124) at com.android.okhttp.internal.http.HttpEngine.connect(HttpEngine.java:272) at com.android.okhttp.internal.http.HttpEngine.sendRequest(HttpEngine.java:211) at com.android.okhttp.internal.http.HttpURLConnectionImpl.execute(HttpURLConnectionImpl.java:373) at com.android.okhttp.internal.http.HttpURLConnectionImpl.getResponse(HttpURLConnectionImpl.java:323) at com.android.okhttp.internal.http.HttpURLConnectionImpl.getInputStream(HttpURLConnectionImpl.java:190) at java.net.URL.openStream(URL.java:470) at com.wc.gap.worldcupfixture.MainActivity.onCreate(MainActivity.java:102) at android.app.Activity.performCreate(Activity.java:5933) at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1105) at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2251)            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)            at android.app.ActivityThread.access$800(ActivityThread.java:144)            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)            at android.os.Handler.dispatchMessage(Handler.java:102)            at android.os.Looper.loop(Looper.java:135)            at android.app.ActivityThread.main(ActivityThread.java:5221)            at java.lang.reflect.Method.invoke(Native Method)            at java.lang.reflect.Method.invoke(Method.java:372)            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694) 

新的InputStreamReader（scoreU.openStream（）））;

Answer 1

使用此代碼：-

try {
        URL url = new URL("http://m.uploadedit.com/b044/1422550899503.txt");
        URLConnection urlConnection = url.openConnection();
        HttpURLConnection connection = null;
        connection = (HttpURLConnection) urlConnection;

        BufferedReader in = new BufferedReader(new InputStreamReader(
                connection.getInputStream()));
        String urlString = "";
        String current;
        while ((current = in.readLine()) != null) {
            urlString += current;
        }
        System.out.println(urlString);
    } catch (IOException e) {
        e.printStackTrace();
    }

Answer 2

Android不允許在主線程上發出網絡請求，因為它可能導致UI無響應。 相反，您必須在后台線程上進行工作，但是使用AsyncTask可以非常輕松地進行此操作，例如：

public class MainActivity extends Activity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        // ...

        // Start the task here
        new URLDataLoader().execute(theURL);
    }

    private class URLDataLoader extends AsyncTask<URL, Void, String> {
        @Override
        protected String doInBackground(URL... params) {
            URL theURL = params[0];
            // Do your network stuff here to get the data
            return theData;
        }

        @Override
        protected void onPostExecute(String data) {
            // Use the data here
        }
    }
}