String response = getResultForRequest(url);
其中'url'是JSON格式的，使用http GET方法返回数据束。
public static String getResultForRequest(String urlString)
throws IOException {
URL url = new URL(urlString);
HttpURLConnection urlConnection = (HttpURLConnection) url
.openConnection();
urlConnection.setRequestMethod("GET");
urlConnection.setDoInput(true);
urlConnection.setDoOutput(true);
urlConnection.connect();
InputStream is = urlConnection.getInputStream();
if (is == null)
return null;
StringBuffer sb = new StringBuffer();
BufferedReader br = new BufferedReader(new InputStreamReader(is));
String line = null;
try {
while ((line = br.readLine()) != null)
sb.append(line);
} finally {
br.close();
is.close();
}
return sb.toString();
}
我无法从我在getResultForRequest（url）方法中传递的'url'获取JSON格式的数据。我在 urlConnection.connect（）; 中出错。 AndroidManifest.xml文件中也提供了Internet权限。
这是我的日志。
10-09 13:27:35.264: E/AndroidRuntime(9984): FATAL EXCEPTION: main
10-09 13:27:35.264: E/AndroidRuntime(9984): java.lang.RuntimeException: Unable to start activity ComponentInfo{}: android.os.NetworkOnMainThreadException
10-09 13:27:35.264: E/AndroidRuntime(9984): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2100)
10-09 13:27:35.264: E/AndroidRuntime(9984): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2125)
10-09 13:27:35.264: E/AndroidRuntime(9984): at android.app.ActivityThread.access$600(ActivityThread.java:140)
10-09 13:27:35.264: E/AndroidRuntime(9984): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1227)
10-09 13:27:35.264: E/AndroidRuntime(9984): at android.os.Handler.dispatchMessage(Handler.java:99)
10-09 13:27:35.264: E/AndroidRuntime(9984): at android.os.Looper.loop(Looper.java:137)
10-09 13:27:35.264: E/AndroidRuntime(9984): at android.app.ActivityThread.main(ActivityThread.java:4898)
10-09 13:27:35.264: E/AndroidRuntime(9984): at java.lang.reflect.Method.invokeNative(Native Method)
10-09 13:27:35.264: E/AndroidRuntime(9984): at java.lang.reflect.Method.invoke(Method.java:511)
10-09 13:27:35.264: E/AndroidRuntime(9984): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1008)
10-09 13:27:35.264: E/AndroidRuntime(9984): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:775)
10-09 13:27:35.264: E/AndroidRuntime(9984): at dalvik.system.NativeStart.main(Native Method)
10-09 13:27:35.264: E/AndroidRuntime(9984): Caused by: android.os.NetworkOnMainThreadException
10-09 13:27:35.264: E/AndroidRuntime(9984): at android.os.StrictMode$AndroidBlockGuardPolicy.onNetwork(StrictMode.java:1118)
10-09 13:27:35.264: E/AndroidRuntime(9984): at java.net.InetAddress.lookupHostByName(InetAddress.java:385)
10-09 13:27:35.264: E/AndroidRuntime(9984): at java.net.InetAddress.getAllByNameImpl(InetAddress.java:236)
10-09 13:27:35.264: E/AndroidRuntime(9984): at java.net.InetAddress.getAllByName(InetAddress.java:214)
10-09 13:27:35.264: E/AndroidRuntime(9984): at libcore.net.http.HttpConnection.<init>(HttpConnection.java:70)
10-09 13:27:35.264: E/AndroidRuntime(9984): at libcore.net.http.HttpConnection.<init>(HttpConnection.java:50)
10-09 13:27:35.264: E/AndroidRuntime(9984): at libcore.net.http.HttpConnection$Address.connect(HttpConnection.java:340)
10-09 13:27:35.264: E/AndroidRuntime(9984): at libcore.net.http.HttpConnectionPool.get(HttpConnectionPool.java:87)
10-09 13:27:35.264: E/AndroidRuntime(9984): at libcore.net.http.HttpConnection.connect(HttpConnection.java:128)
10-09 13:27:35.264: E/AndroidRuntime(9984): at libcore.net.http.HttpEngine.openSocketConnection(HttpEngine.java:315)
10-09 13:27:35.264: E/AndroidRuntime(9984): at libcore.net.http.HttpsURLConnectionImpl$HttpsEngine.makeSslConnection(HttpsURLConnectionImpl.java:461)
10-09 13:27:35.264: E/AndroidRuntime(9984): at libcore.net.http.HttpsURLConnectionImpl$HttpsEngine.connect(HttpsURLConnectionImpl.java:433)
10-09 13:27:35.264: E/AndroidRuntime(9984): at libcore.net.http.HttpEngine.sendSocketRequest(HttpEngine.java:289)
10-09 13:27:35.264: E/AndroidRuntime(9984): at libcore.net.http.HttpEngine.sendRequest(HttpEngine.java:239)
10-09 13:27:35.264: E/AndroidRuntime(9984): at libcore.net.http.HttpURLConnectionImpl.connect(HttpURLConnectionImpl.java:80)
10-09 13:27:35.264: E/AndroidRuntime(9984): at libcore.net.http.HttpsURLConnectionImpl.connect(HttpsURLConnectionImpl.java:165)
10-09 13:27:35.264: E/AndroidRuntime(9984): at com.csoft.foursquare.FoursquareService.getResultForRequest(Service.java:564)
10-09 13:27:35.264: E/AndroidRuntime(9984): at com.csoft.foursquare.FoursquareService.getUserDetails(Service.java:376)
10-09 13:27:35.264: E/AndroidRuntime(9984): at com.csoft.checkin.CheckinHistoryActivity.onCreate(HistoryActivity.java:52)
10-09 13:27:35.264: E/AndroidRuntime(9984): at android.app.Activity.performCreate(Activity.java:5206)
10-09 13:27:35.264: E/AndroidRuntime(9984): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1094)
10-09 13:27:35.264: E/AndroidRuntime(9984): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2064)
10-09 13:27:35.264: E/AndroidRuntime(9984): ... 11 more
先谢谢。
答案 0 :(得分：28)
在onCreate（）中添加：
StrictMode.ThreadPolicy policy = new StrictMode.ThreadPolicy.Builder().permitAll().build();
StrictMode.setThreadPolicy(policy);
使用以上作为临时解决方案。否则使用线程或asynctask。
答案 1 :(得分：12)
您正在尝试在主（UI）线程上建立网络连接。这在Android中是不允许的，因为在您从服务器获得响应之前它将暂停整个UI。
尝试使用AsyncTask，或在单独的线程上执行连接。
希望这有帮助。
答案 2 :(得分：2)
NetworkOnMainThreadException：应用程序尝试在其主线程上执行网络操作时引发的异常。
你应该在asynctask上调用方法然后只有代码才能工作。要避免它，你应该在另一个线程上调用它。因此asynctask更好。
http://android-developers.blogspot.in/2009/05/painless-threading.html
http://android-er.blogspot.in/2012/04/androidosnetworkonmainthreadexception.html
http://www.lucazanini.eu/2012/android/the-android-os-networkonmainthreadexception-exception/?lang=en
这里是说明如何使用asynctask
的链接