Question

我现在正试图使用API;第一次使用API，第一次尝试在Android上做某事，所以我不确定我在做什么。

首先，我有这个：

InputStream in = null;


        try {

            URL url = new URL(urlGetTerm);


            HttpURLConnection urlConnection = (HttpURLConnection) url.openConnection();


            in = new BufferedInputStream(urlConnection.getInputStream());


        } catch (Exception e ) {

            System.out.println(e.getMessage());

            return lst;

        }

我发现它在in = newBufferedInputStream（url.Connection.getInputStream（））中崩溃了; 将日志消息放到各处后。

为什么会崩溃？当我连接＆＃39;使用urlConnection到API网址，不应该让getInputStream给我json响应吗？正确访问urlGetTerm的url会将我带到一个带有json响应的页面，因此实际的url没有任何问题。

日志：

10-18 14:58:20.356  30708-30708/com.example.naomikoo.classalert E/AndroidRuntime﹕ FATAL EXCEPTION: main
    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.naomikoo.classalert/com.example.naomikoo.classalert.MainActivity}: java.lang.NullPointerException
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2180)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230)
            at android.app.ActivityThread.access$600(ActivityThread.java:141)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234)
            at android.os.Handler.dispatchMessage(Handler.java:99)
            at android.os.Looper.loop(Looper.java:137)
            at android.app.ActivityThread.main(ActivityThread.java:5039)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:511)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
            at dalvik.system.NativeStart.main(Native Method)
     Caused by: java.lang.NullPointerException
            at com.android.internal.os.LoggingPrintStream.println(LoggingPrintStream.java:298)
            at com.example.naomikoo.classalert.uwApi.getResult(uwApi.java:50)
            at com.example.naomikoo.classalert.MainActivity.onCreate(MainActivity.java:75)
            at android.app.Activity.performCreate(Activity.java:5104)
            at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1080)
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2144)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230)
            at android.app.ActivityThread.access$600(ActivityThread.java:141)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234)
            at android.os.Handler.dispatchMessage(Handler.java:99)
            at android.os.Looper.loop(Looper.java:137)
            at android.app.ActivityThread.main(ActivityThread.java:5039)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:511)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
            at dalvik.system.NativeStart.main(Native Method)

Answer 1

删除System.out.println(e.getMessage());。 e.getMessage()为null。

您无法在主线程上进行网络操作当应用程序尝试在其主线程上执行网络操作时，将抛出异常（NetworkOnMainThreadException）。

使用以下代码来避免此错误，或者在线程或AsyncTask中调用您的网络操作。

    if (android.os.Build.VERSION.SDK_INT > 9)
    {
        StrictMode.ThreadPolicy policy = new StrictMode.ThreadPolicy.Builder().permitAll().build();
        StrictMode.setThreadPolicy(policy);
    }

试图使用api; bufferedinputstream导致崩溃？

1 个答案: