Android -从URL下载json数据

Question

我正在使用Google Directions API获取到达位置之间的时间，并尝试将URL中的数据转换为JSON对象，以便我可以解析它以获取所需的数据。URL为：

http://maps.googleapis.com/maps/api/directions/json?origin=Chicago,IL&destination=Los+Angeles,CA&waypoints=Joplin,MO|Oklahoma+City,OK&sensor=false

我使用一个意图转到这个URL。

String url = "http://maps.googleapis.com/maps/api/directions/json?origin=Chicago,IL&destination=Los+Angeles,CA&waypoints=Joplin,MO|Oklahoma+City,OK&sensor=false"
Intent intent = new Intent(android.content.Intent.ACTION_VIEW, Uri.parse(url));
startActivity(intent);

这将在浏览器中显示json数据，我想将其放入一个json对象中，这样我就可以使用以下命令获取所需的任何数据：

JSONObject durationObject = null; 
durationObject = jsonObject.getJSONObject("duration");

我已经在网上查过了，但我尝试的所有东西都以崩溃或不工作而告终。下面是我试过的一些代码，但不起作用。因为执行了if语句，所以没有任何东西最终被写入字符串结果。

InputStream is = null;
String result = "";
JSONObject jsonObject = null;
try {   
    HttpClient httpclient = new DefaultHttpClient(); // for port 80 requests!
    HttpPost httppost = new HttpPost(url);
    HttpResponse response = httpclient.execute(httppost);
    HttpEntity entity = response.getEntity();
    is = entity.getContent();

    // Read response to string
    BufferedReader reader = new BufferedReader(new InputStreamReader(is,"utf-8"),1024);
    StringBuilder sb = new StringBuilder();
    String line = "";
    while ((line = reader.readLine()) != null) {
    sb.append(line + "\n");
    }
    is.close();
    result = sb.toString(); 


    if (result.isEmpty()) { 
        result = "nothing"; 
        Toast msg = Toast.makeText(getBaseContext(), result, Toast.LENGTH_LONG);
    msg.show();
    }
 // Convert string to object

    jsonObject = new JSONObject(result);

这是logcat的输出：

04-16 18:38:42.965: W/dalvikvm(9331): threadid=1: thread exiting with uncaught exception (group=0x40c371f8)
04-16 18:38:42.975: E/AndroidRuntime(9331): FATAL EXCEPTION: main
04-16 18:38:42.975: E/AndroidRuntime(9331): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.test/com.example.test.MainActivity}: android.os.NetworkOnMainThreadException
04-16 18:38:42.975: E/AndroidRuntime(9331):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1968)
04-16 18:38:42.975: E/AndroidRuntime(9331):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1993)
04-16 18:38:42.975: E/AndroidRuntime(9331):     at android.app.ActivityThread.access$600(ActivityThread.java:127)
04-16 18:38:42.975: E/AndroidRuntime(9331):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1159)
04-16 18:38:42.975: E/AndroidRuntime(9331):     at android.os.Handler.dispatchMessage(Handler.java:99)
04-16 18:38:42.975: E/AndroidRuntime(9331):     at android.os.Looper.loop(Looper.java:137)
04-16 18:38:42.975: E/AndroidRuntime(9331):     at android.app.ActivityThread.main(ActivityThread.java:4507)
04-16 18:38:42.975: E/AndroidRuntime(9331):     at java.lang.reflect.Method.invokeNative(Native Method)
04-16 18:38:42.975: E/AndroidRuntime(9331):     at java.lang.reflect.Method.invoke(Method.java:511)
04-16 18:38:42.975: E/AndroidRuntime(9331):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:790)
04-16 18:38:42.975: E/AndroidRuntime(9331):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:557)
04-16 18:38:42.975: E/AndroidRuntime(9331):     at dalvik.system.NativeStart.main(Native Method)
04-16 18:38:42.975: E/AndroidRuntime(9331): Caused by: android.os.NetworkOnMainThreadException
04-16 18:38:42.975: E/AndroidRuntime(9331):     at android.os.StrictMode$AndroidBlockGuardPolicy.onNetwork(StrictMode.java:1099)
04-16 18:38:42.975: E/AndroidRuntime(9331):     at java.net.InetAddress.lookupHostByName(InetAddress.java:391)
04-16 18:38:42.975: E/AndroidRuntime(9331):     at java.net.InetAddress.getAllByNameImpl(InetAddress.java:242)
04-16 18:38:42.975: E/AndroidRuntime(9331):     at java.net.InetAddress.getAllByName(InetAddress.java:220)
04-16 18:38:42.975: E/AndroidRuntime(9331):     at org.apache.http.impl.conn.DefaultClientConnectionOperator.openConnection(DefaultClientConnectionOperator.java:137)
04-16 18:38:42.975: E/AndroidRuntime(9331):     at org.apache.http.impl.conn.AbstractPoolEntry.open(AbstractPoolEntry.java:164)
04-16 18:38:42.975: E/AndroidRuntime(9331):     at org.apache.http.impl.conn.AbstractPooledConnAdapter.open(AbstractPooledConnAdapter.java:119)
04-16 18:38:42.975: E/AndroidRuntime(9331):     at org.apache.http.impl.client.DefaultRequestDirector.execute(DefaultRequestDirector.java:360)
04-16 18:38:42.975: E/AndroidRuntime(9331):     at org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:555)
04-16 18:38:42.975: E/AndroidRuntime(9331):     at org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:487)
04-16 18:38:42.975: E/AndroidRuntime(9331):     at org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:465)
04-16 18:38:42.975: E/AndroidRuntime(9331):     at com.example.test.MainActivity.onCreate(MainActivity.java:93)
04-16 18:38:42.975: E/AndroidRuntime(9331):     at android.app.Activity.performCreate(Activity.java:4465)
04-16 18:38:42.975: E/AndroidRuntime(9331):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1052)
04-16 18:38:42.975: E/AndroidRuntime(9331):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1932)
04-16 18:38:42.975: E/AndroidRuntime(9331):     ... 11 more

我正在研究它，它似乎与启用严格模式有关。任何关于如何解决这个问题的帮助都将是很好的。

Answer 1

这里发生的事情很常见，你试图在你的应用程序的主线程上执行一些长时间运行的操作。

这意味着，主线程负责更新UI，以增强流畅的体验，如果android检测到您正在执行一些将被阻塞的长时间运行的操作，它将强制关闭应用程序，让您知道这是错误的。

有许多替代解决方案，例如AsynTask或IntentService。

IntentService是一个在您向其发送意图时运行的服务：

public class NetworkHandler extends IntentService {
    @Override
    protected void onHandleIntent(Intent intent) {
         //Do what Saeid Farivar is saying here
    }
}

要激活IntentService，只需执行以下操作：

Intent intent = new Intent(mContext, NetworkHandler.class);
startService(intent);

Answer 2

这是我正在使用的工作代码

    private DefaultHttpClient httpclient = new DefaultHttpClient();

    public JSONObject getObjectInfo(String requestURL) throws Exception {

    JSONObject responseObject = null;
    Log.d(getClass().getSimpleName(), "HttpClient: getObjectInfo: "
            + requestURL);
    HttpGet httpget = new HttpGet(requestURL);
    HttpResponse response;
    try {
        response = httpclient.execute(httpget);
        HttpEntity entity = response.getEntity();
        Log.d(getClass().getSimpleName(), "HttpClient: getObjectInfo: "
                + "respondreceived");
        if (entity != null) {
            InputStream instream = entity.getContent();
            Log.d("httpclient",
                    "HttpClient: getObjectInfo: converting to string");
            String jsonObjectString = Conversion
                    .convertStreamToString(instream);

            try {
                responseObject = new JSONObject(jsonObjectString);
            } catch (JSONException e) {
                e.printStackTrace();
            }
        }
    } catch (IOException e) {
        e.printStackTrace();
    } catch (IllegalStateException e1) {
        e1.printStackTrace();
    } finally {

    }
    return responseObject;
}

将流转换为字符串的方法：

    public static String convertStreamToString(java.io.InputStream is) {

    try {
        return new java.util.Scanner(is).useDelimiter("\\A").next();
    } catch (java.util.NoSuchElementException e) {
        return "";
    }
}

也就是说，我建议使用Jakson库从接收到的json对象创建一个类，here就是一个使用Jakson库的例子。