我正在开发一个应用程序，其中从服务器获取数据的过程是
步骤1：使用Http POST将请求发布到具有特定标题内容的url。
第2步：作为回报，我将获得一个链接的一部分，我必须构建一个完整的URL
Strp 3：现在，使用Http GET方法传递此URL以获取数据。
现在我正在尝试使用以下代码实现此目的，
@Override
protected String doInBackground(String... params)
{
try
{
/** Performing POST method to url to obtain link for data**/
HttpClient httpClient = HttpClientConstant.getThreadSafeClient();
HttpPost httpPost = new HttpPost(CHANNEL_LANGUAGE_SENTIMENT_URL);
httpPost.setEntity(new ByteArrayEntity(POST_URL_VALUES.toString().getBytes("UTF8")));
HttpResponse response = httpClient.execute(httpPost);
if(response!=null)
{
OBTAIN_URL_LINK = convertJsonToString(response.getEntity().getContent()).toString();
/** getting the link in OBTAIN_URL_LINK**/
System.out.println("Response: " + OBTAIN_URL_LINK);
try
{
/** Constructing the URL**/
JSONObject mainStringJSON = new JSONObject(OBTAIN_URL_LINK);
REFINED_URL_LINK = mainStringJSON.getString("poll_url");
REQUIRED_URL_LINK = PREDEFINED_URL_LINK + REFINED_URL_LINK;
System.out.println("URL to USE: " + REQUIRED_URL_LINK);
/** Performing GET method to obtain the Data**/
HttpClient channelHttpClient = HttpClientConstant.getThreadSafeClient();
HttpGet channelHttpGet = new HttpGet(REQUIRED_URL_LINK);
HttpResponse channelHttpResponse = channelHttpClient.execute(channelHttpGet);
/** Reading the JSON response and stroing in string**/
BufferedReader channelHttpReader = new BufferedReader(new InputStreamReader(channelHttpResponse.getEntity().getContent(), "UTF-8") );
CHANNEL_LANGUAGE_RESPONSE_JSON = channelHttpReader.readLine();
System.out.println(CHANNEL_LANGUAGE_RESPONSE_JSON);
if(CHANNEL_LANGUAGE_RESPONSE_JSON != null)
{
try
{
JSONObject mainJson = new JSONObject(CHANNEL_LANGUAGE_RESPONSE_JSON);
JSONObject dataJson = mainJson.getJSONObject("data");
//JSONObject dataJson = new JSONObject().getJSONObject("data");
/** Values for Channel Graphs**/
JSONObject channelJson = dataJson.getJSONObject("category");
int twitterValues = channelJson.getInt("twitter");
当我调试应用程序时，它工作正常，它显示数据。但是，当我运行应用程序时，它会崩溃并给我这个，
10-07 09:03:10.517: I/System.out(1330): org.json.JSONException: No value for data
10-07 09:03:10.517: I/System.out(1330): at org.json.JSONObject.get(JSONObject.java:354)
10-07 09:03:10.517: I/System.out(1330): at org.json.JSONObject.getJSONObject(JSONObject.java:569)
10-07 09:03:10.557: I/System.out(1330): at m_brain.m_adaptive.m_DetailActivity.ChannelsAndLanguageFilterFragment$GetChannelAndLanguageData.doInBackground(ChannelsAndLanguageFilterFragment.java:164)
10-07 09:03:10.597: I/System.out(1330): at m_brain.m_adaptive.m_DetailActivity.ChannelsAndLanguageFilterFragment$GetChannelAndLanguageData.doInBackground(ChannelsAndLanguageFilterFragment.java:1)
10-07 09:03:10.597: I/System.out(1330): at android.os.AsyncTask$2.call(AsyncTask.java:287)
10-07 09:03:10.637: I/System.out(1330): at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:305)
10-07 09:03:10.637: I/System.out(1330): at java.util.concurrent.FutureTask.run(FutureTask.java:137)
10-07 09:03:10.637: I/System.out(1330): at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:230)
10-07 09:03:10.669: I/System.out(1330): at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1076)
10-07 09:03:10.708: I/System.out(1330): at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:569)
10-07 09:03:10.747: I/System.out(1330): at java.lang.Thread.run(Thread.java:856)
10-07 09:03:10.917: I/Choreographer(1330): Skipped 35 frames! The application may be doing too much work on its main thread.
10-07 09:03:11.047: D/AndroidRuntime(1330): Shutting down VM
10-07 09:03:11.047: W/dalvikvm(1330): threadid=1: thread exiting with uncaught exception (group=0x40a13300)
10-07 09:03:11.077: E/AndroidRuntime(1330): FATAL EXCEPTION: main
10-07 09:03:11.077: E/AndroidRuntime(1330): java.lang.IndexOutOfBoundsException: Invalid index 0, size is 0
10-07 09:03:11.077: E/AndroidRuntime(1330): at java.util.ArrayList.throwIndexOutOfBoundsException(ArrayList.java:251)
10-07 09:03:11.077: E/AndroidRuntime(1330): at java.util.ArrayList.get(ArrayList.java:304)
10-07 09:03:11.077: E/AndroidRuntime(1330): at m_brain.m_adaptive.m_DetailActivity.ChannelsAndLanguageFilterFragment.generatePieDataChannels(ChannelsAndLanguageFilterFragment.java:311)
10-07 09:03:11.077: E/AndroidRuntime(1330): at m_brain.m_adaptive.m_DetailActivity.ChannelsAndLanguageFilterFragment.access$11(ChannelsAndLanguageFilterFragment.java:304)
10-07 09:03:11.077: E/AndroidRuntime(1330): at m_brain.m_adaptive.m_DetailActivity.ChannelsAndLanguageFilterFragment$GetChannelAndLanguageData.onPostExecute(ChannelsAndLanguageFilterFragment.java:270)
10-07 09:03:11.077: E/AndroidRuntime(1330): at m_brain.m_adaptive.m_DetailActivity.ChannelsAndLanguageFilterFragment$GetChannelAndLanguageData.onPostExecute(ChannelsAndLanguageFilterFragment.java:1)
10-07 09:03:11.077: E/AndroidRuntime(1330): at android.os.AsyncTask.finish(AsyncTask.java:631)
10-07 09:03:11.077: E/AndroidRuntime(1330): at android.os.AsyncTask.access$600(AsyncTask.java:177)
10-07 09:03:11.077: E/AndroidRuntime(1330): at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:644)
10-07 09:03:11.077: E/AndroidRuntime(1330): at android.os.Handler.dispatchMessage(Handler.java:99)
10-07 09:03:11.077: E/AndroidRuntime(1330): at android.os.Looper.loop(Looper.java:137)
10-07 09:03:11.077: E/AndroidRuntime(1330): at android.app.ActivityThread.main(ActivityThread.java:4745)
10-07 09:03:11.077: E/AndroidRuntime(1330): at java.lang.reflect.Method.invokeNative(Native Method)
10-07 09:03:11.077: E/AndroidRuntime(1330): at java.lang.reflect.Method.invoke(Method.java:511)
10-07 09:03:11.077: E/AndroidRuntime(1330): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
10-07 09:03:11.077: E/AndroidRuntime(1330): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
10-07 09:03:11.077: E/AndroidRuntime(1330): at dalvik.system.NativeStart.main(Native Method)
我在片段中执行此操作并在ListView中显示图形中的数据。我是初学者，所以如果我以错误的方式做这件事或需要不同的方法，请指导我。此外，由于Http请求或其他任何原因，我无法理解这是否是hapening。它显示的行指向try方法的结尾。
答案 0 :(得分：2)
您可以使用此类来处理：
import java.io.IOException;
import java.io.UnsupportedEncodingException;
import java.util.List;
import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.NameValuePair;
import org.apache.http.client.ClientProtocolException;
import org.apache.http.client.entity.UrlEncodedFormEntity;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.client.utils.URLEncodedUtils;
import org.apache.http.impl.client.DefaultHttpClient;
import org.apache.http.util.EntityUtils;
import org.json.JSONException;
import org.json.JSONObject;
import android.util.Log;
public class ServiceHandler
{
private JSONObject response = null;
public final static int GET = 1;
public final static int POST = 2;
public JSONObject makeServiceCall( String url, int method )
{
return this.makeServiceCall( url, method, null );
}
public JSONObject makeServiceCall( String url, int method, List<NameValuePair> params )
{
try
{
DefaultHttpClient httpClient = new DefaultHttpClient();
HttpEntity httpEntity = null;
HttpResponse httpResponse = null;
if( method == POST )
{
HttpPost httpPost = new HttpPost( url );
if( params != null )
{
httpPost.setEntity( new UrlEncodedFormEntity( params, "UTF-8" ) );
}
httpResponse = httpClient.execute( httpPost );
}else if( method == GET )
{
if( params != null )
{
String paramString = URLEncodedUtils.format( params, "UTF-8" );
url += "?" + paramString;
}
HttpGet httpGet = new HttpGet( url );
//Envia a URL e pega a resposta.
httpResponse = httpClient.execute( httpGet );
}
httpClient = null;
httpEntity = httpResponse.getEntity();
httpResponse = null;
String JSONString = EntityUtils.toString( httpEntity );
Log.e( "JSON", JSONString );
try
{
response = new JSONObject( JSONString );
}catch( JSONException e ) { }
httpEntity = null;
}catch( UnsupportedEncodingException e )
{
e.printStackTrace();
}catch( ClientProtocolException e )
{
e.printStackTrace();
}catch( IOException e )
{
e.printStackTrace();
}
return response;
}
}
使用方法：
ServiceHandler serviceHandler = new ServiceHandler();
JSONObject jsonObj = serviceHandler.makeServiceCall( URL, ServiceHandler.POST OR ServiceHandler.GET, PARAMS );
答案 1 :(得分：0)
http://developer.android.com/reference/org/json/JSONObject.html#getJSONObject(java.lang.String)
如果映射不存在或不是JSONObject，则抛出JSONException。
JSONObject dataJson = mainJson.getJSONObject("data");
这失败了，因为与＆＃34;数据＆＃34;相关联的对象不存在。
使用has方法确保它存在
if (mainJson.has("data"))
{
JSONObject dataJson = mainJson.getJSONObject("data");
JSONObject channelJson = dataJson.getJSONObject("category");
// [...]
}