尝试从Google Alert Feed解析时出现java.lang.NullPointerException错误

时间：2014-10-13 02:35:31

标签： java android android-asynctask rss google-alerts

我已经从Google Alerts Source制作了一个Android RSS Feed应用程序。我编译并运行后只显示空白屏幕但没有崩溃。您可以查看我的脚本中的错误，如下所示：

来自ListRSSItemsActivity.java：

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;



import android.app.ListActivity;
import android.app.ProgressDialog;
import android.content.Intent;
import android.os.AsyncTask;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemClickListener;
import android.widget.ImageButton;
import android.widget.ListAdapter;
import android.widget.ListView;
import android.widget.SimpleAdapter;
import android.widget.TextView;

public class ListRSSItemsActivity extends ListActivity {

    // Progress Dialog
    private ProgressDialog pDialog;

    // Array list for list view
    ArrayList<HashMap<String, String>> rssItemList = new ArrayList<HashMap<String,String>>();

    RSSParser rssParser = new RSSParser();

    // button add new website
    ImageButton btnAddSite;

    List<RSSItem> rssItems = new ArrayList<RSSItem>();

    RSSFeed rssFeed;

    private static String TAG_TITLE = "title";
    private static String TAG_LINK = "link";
    private static String TAG_DESRIPTION = "description";
    private static String TAG_PUB_DATE = "pubDate";
    private static String TAG_GUID = "guid"; // not used
    private String urlString = "http://www.google.com/alerts/feeds/01662123773360489091/16526224428036307178";

    @Override
     public void onCreate(Bundle paramBundle)
      {
        super.onCreate(paramBundle);
        setContentView(R.layout.rss_item_list);
        String str = urlString;
        new loadRSSFeed().execute(str);
        getListView().setOnItemClickListener(new AdapterView.OnItemClickListener()
        {
          public void onItemClick(AdapterView<?> paramAdapterView, View paramView, int paramInt, long paramLong)
          {
            Intent localIntent = new Intent(ListRSSItemsActivity.this.getApplicationContext(), DisPlayWebPageActivity.class);
            localIntent.putExtra("page_url", ((TextView)paramView.findViewById(R.id.page_url)).getText().toString());
            ListRSSItemsActivity.this.startActivity(localIntent);
          }
        });
      }

      class loadRSSFeed extends AsyncTask<String, String, String>
      {
        loadRSSFeed()
        {
        }

        protected String doInBackground(String[] paramArrayOfString)
        {
          String str1 = paramArrayOfString[0];
          ListRSSItemsActivity.this.rssFeed = ListRSSItemsActivity.this.rssParser.getRSSFeed(str1);
          Log.d("rssFeed", "rssFeed: " + ListRSSItemsActivity.this.rssFeed);
          Log.d("rssFeed", "url: " + str1);
          if (ListRSSItemsActivity.this.rssFeed != null)
          {
            Log.e("RSS URL", ListRSSItemsActivity.this.rssFeed.getTitle() + ListRSSItemsActivity.this.rssFeed.getLink() + ListRSSItemsActivity.this.rssFeed.getDescription() + ListRSSItemsActivity.this.rssFeed.getLanguage());
            WebSite localWebSite = new WebSite(ListRSSItemsActivity.this.rssFeed.getTitle(), ListRSSItemsActivity.this.rssFeed.getLink(), ListRSSItemsActivity.this.rssFeed.getRSSLink(), ListRSSItemsActivity.this.rssFeed.getDescription());
            HashMap localHashMap = new HashMap();
            localHashMap.put(ListRSSItemsActivity.TAG_TITLE, localWebSite.getTitle());
            localHashMap.put(ListRSSItemsActivity.TAG_LINK, localWebSite.getLink());
            String str2 = localWebSite.getDescription();
            if (str2.length() > 100)
              str2 = str2.substring(0, 97) + "..";
            localHashMap.put(ListRSSItemsActivity.TAG_DESRIPTION, str2);
            ListRSSItemsActivity.this.rssItemList.add(localHashMap);
          }
          ListRSSItemsActivity.this.runOnUiThread(new Runnable()
          {
            public void run()
            {
              ListRSSItemsActivity localListRSSItemsActivity = ListRSSItemsActivity.this;
              ArrayList localArrayList = ListRSSItemsActivity.this.rssItemList;
              String[] arrayOfString = new String[4];
              arrayOfString[0] = ListRSSItemsActivity.TAG_LINK;
              arrayOfString[1] = ListRSSItemsActivity.TAG_TITLE;
              arrayOfString[2] = ListRSSItemsActivity.TAG_PUB_DATE;
              arrayOfString[3] = ListRSSItemsActivity. TAG_DESRIPTION;
              SimpleAdapter localSimpleAdapter = new SimpleAdapter(localListRSSItemsActivity, localArrayList, R.layout.rss_item_list_row, arrayOfString, new int[] { R.id.page_url, R.id.title , R.id.pub_date, R.id.link  });
              ListRSSItemsActivity.this.setListAdapter(localSimpleAdapter);
            }
          });
          return null;
        }

        protected void onPostExecute(String paramString)
        {
          ListRSSItemsActivity.this.pDialog.dismiss();
        }

        protected void onPreExecute()
        {
          super.onPreExecute();
          ListRSSItemsActivity.this.pDialog = new ProgressDialog(ListRSSItemsActivity.this);
          ListRSSItemsActivity.this.pDialog.setMessage("Fetching RSS Information ...");
          ListRSSItemsActivity.this.pDialog.setIndeterminate(false);
          ListRSSItemsActivity.this.pDialog.setCancelable(false);
          ListRSSItemsActivity.this.pDialog.show();
        }
      }

}

来自RSSParser.java 

import android.text.Html;
import android.text.Spanned;
import android.util.Log;
import java.io.IOException;
import java.io.StringReader;
import java.io.UnsupportedEncodingException;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.ArrayList;
import java.util.Date;
import java.util.List;
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.ParserConfigurationException;
import org.apache.http.HttpResponse;
import org.apache.http.client.ClientProtocolException;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.DefaultHttpClient;
import org.apache.http.util.EntityUtils;
import org.w3c.dom.Document;
import org.w3c.dom.Element;
import org.w3c.dom.Node;
import org.w3c.dom.NodeList;
import org.xml.sax.InputSource;
import org.xml.sax.SAXException;

public class RSSParser
{
  private static String TAG_CHANNEL = "channel";
  private static String TAG_DESRIPTION;
  private static String TAG_GUID;
  private static String TAG_ITEM;
  private static String TAG_LANGUAGE;
  private static String TAG_LINK;
  private static String TAG_PUB_DATE;
  private static String TAG_TITLE = "title";

  static
  {
    TAG_LINK = "link";
    TAG_DESRIPTION = "content";
    TAG_LANGUAGE = "language";
    TAG_ITEM = "entry";
    TAG_PUB_DATE = "published";
    TAG_GUID = "guid";
  }

  private String setTime(String paramString)
  {
    String str1 = paramString.substring(0, 10) + " " + paramString.substring(11, 19);
    Log.d("date", str1);
    SimpleDateFormat localSimpleDateFormat = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
    try
    {
      String str2 = localSimpleDateFormat.format(new Date(25200000L + localSimpleDateFormat.parse(str1).getTime()));
      return str2;
    }
    catch (ParseException localParseException)
    {
      localParseException.printStackTrace();
    }
    return str1;
  }

  public Document getDomElement(String paramString)
  {
    DocumentBuilderFactory localDocumentBuilderFactory = DocumentBuilderFactory.newInstance();
    try
    {
      DocumentBuilder localDocumentBuilder = localDocumentBuilderFactory.newDocumentBuilder();
      InputSource localInputSource = new InputSource();
      localInputSource.setCharacterStream(new StringReader(paramString));
      Document localDocument = localDocumentBuilder.parse(localInputSource);
      return localDocument;
    }
    catch (ParserConfigurationException localParserConfigurationException)
    {
      Log.e("Error: ", localParserConfigurationException.getMessage());
      return null;
    }
    catch (SAXException localSAXException)
    {
      Log.e("Error: ", localSAXException.getMessage());
      return null;
    }
    catch (IOException localIOException)
    {
      Log.e("Error: ", localIOException.getMessage());
    }
    return null;
  }

  public final String getElementValue(Node paramNode)
  {
    if ((paramNode != null) && (paramNode.hasChildNodes()));
    for (Node localNode = paramNode.getFirstChild(); ; localNode = localNode.getNextSibling())
    {
      if (localNode == null)
        return "";
      if ((localNode.getNodeType() == 3) || (localNode.getNodeType() == 4))
        return localNode.getNodeValue();
    }
  }

  public RSSFeed getRSSFeed(String paramString)
  {
    if (paramString != null)
    {
      String str1 = getXmlFromUrl(paramString);
      if (str1 != null)
        try
        {
          Element localElement = (Element)getDomElement(str1).getElementsByTagName(TAG_CHANNEL).item(0);
          String str2 = getValue(localElement, TAG_TITLE);
          String str3 = getValue(localElement, TAG_LINK);
          RSSFeed localRSSFeed = new RSSFeed(str2, getValue(localElement, TAG_DESRIPTION), str3, paramString, getValue(localElement, TAG_LANGUAGE));
          return localRSSFeed;
        }
        catch (Exception localException)
        {
          localException.printStackTrace();
        }
    }
    return null;
  }

  public List<RSSItem> getRSSFeedItems(String paramString)
  {
    ArrayList localArrayList = new ArrayList();
    String str1 = getXmlFromUrl(paramString);
    if (str1 != null)
      try
      {
        NodeList localNodeList1 = getDomElement(str1).getElementsByTagName(TAG_ITEM);
        for (int i = 0; ; i++)
        {
          if (i >= localNodeList1.getLength())
            return localArrayList;
          Element localElement = (Element)localNodeList1.item(i);
          String str2 = Html.fromHtml(getValue(localElement, TAG_TITLE)).toString();
          NodeList localNodeList2 = localElement.getElementsByTagName(TAG_LINK);
          localElement.getAttribute("href");
          localArrayList.add(new RSSItem(str2, ((Element)localNodeList2.item(0)).getAttribute("href").split("&")[0].replace("https://www.google.com/url?q=", ""), Html.fromHtml(getValue(localElement, TAG_DESRIPTION)).toString(), setTime(getValue(localElement, TAG_PUB_DATE)), getValue(localElement, TAG_GUID)));
        }
      }
      catch (Exception localException)
      {
        localException.printStackTrace();
      }
    return localArrayList;
  }

  public String getValue(Element paramElement, String paramString)
  {
    return getElementValue(paramElement.getElementsByTagName(paramString).item(0));
  }

  public String getXmlFromUrl(String paramString)
  {
    try
    {
      String str = EntityUtils.toString(new DefaultHttpClient().execute(new HttpGet(paramString)).getEntity());
      return str;
    }
    catch (UnsupportedEncodingException localUnsupportedEncodingException)
    {
      localUnsupportedEncodingException.printStackTrace();
      return null;
    }
    catch (ClientProtocolException localClientProtocolException)
    {
      localClientProtocolException.printStackTrace();
      return null;
    }
    catch (IOException localIOException)
    {
      localIOException.printStackTrace();
    }
    return null;
  }
}

来自rss_item_list.xml 

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:orientation="vertical"
    android:background="#ffffff">

    <!-- Header -->
    <include layout="@layout/header"/>

    <ListView
        android:id="@android:id/list"
        android:layout_below="@id/layoutHeader"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:divider="#bababa"
        android:dividerHeight="1dp"
        android:listSelector="@drawable/list_selector" 
        android:background="#ffffff" 
        android:cacheColorHint="#00000000"/>

</RelativeLayout>

来自rss_item_list_row.xml 

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    android:orientation="vertical"
    android:padding="8dip" >

    <TextView android:id="@+id/page_url"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:visibility="gone"/>

    <!-- Article title -->
    <TextView
        android:id="@+id/title"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:paddingBottom="1dip"
        android:textSize="18dip"
        android:textStyle="bold"
        android:textColor="#303030" />

    <!-- published date -->
    <TextView 
        android:id="@+id/pub_date"
        android:layout_below="@id/title"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:paddingBottom="3dip"
        android:textSize="14dip"
        android:textColor="#b70400"/>

    <!-- article description -->
    <TextView android:id="@+id/link"
        android:layout_height="wrap_content"
        android:layout_width="wrap_content"
        android:paddingBottom="6dip"
        android:textSize="15dip"
        android:textColor="#8d8d8d"
        android:layout_below="@id/pub_date"/>
</RelativeLayout>

My Error Logcat：

10-12 21:29:26.353: W/System.err(1697): java.lang.NullPointerException
10-12 21:29:26.353: W/System.err(1697):     at com.a.b.RSSParser.getValue(RSSParser.java:157)
10-12 21:29:26.353: W/System.err(1697):     at com.a.b.RSSParser.getRSSFeed(RSSParser.java:116)
10-12 21:29:26.353: W/System.err(1697):     at com.a.b.ListRSSItemsActivity$loadRSSFeed.doInBackground(ListRSSItemsActivity.java:75)
10-12 21:29:26.363: W/System.err(1697):     at com.a.b.ListRSSItemsActivity$loadRSSFeed.doInBackground(ListRSSItemsActivity.java:1)
10-12 21:29:26.363: W/System.err(1697):     at android.os.AsyncTask$2.call(AsyncTask.java:288)
10-12 21:29:26.363: W/System.err(1697):     at java.util.concurrent.FutureTask.run(FutureTask.java:237)
10-12 21:29:26.363: W/System.err(1697):     at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:231)
10-12 21:29:26.363: W/System.err(1697):     at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1112)
10-12 21:29:26.363: W/System.err(1697):     at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:587)
10-12 21:29:26.363: W/System.err(1697):     at java.lang.Thread.run(Thread.java:841)
10-13 09:00:01.940: D/rssFeed(1816): rssFeed: null
10-13 09:00:01.940: D/rssFeed(1816): url: http://www.google.com/alerts/feeds/01662123773360489091/16526224428036307178

我该如何解决？

1 个答案:

答案 0 :(得分：0)

在这个方法中

public String getValue(Element paramElement, String paramString) {
    return getElementValue(paramElement.getElementsByTagName(paramString).item(0));
}

parentElement或paramElement.getElementsByTagName(paramString)为空。运行调试器来搞清楚。

修改

你正在提取

private String urlString = "http://www.google.com/alerts/feeds/01662123773360489091/16526224428036307178";

在目标xml文档中，您正在寻找通道节点

private static String TAG_CHANNEL = "channel";
// [...]
Element localElement = (Element)getDomElement(str1).getElementsByTagName(TAG_CHANNEL).item(0);

但文档中没有这样的标记。所以localElement为null（item（0）返回null）。因此，在此getValue调用中触发NullPointerException（如本文开头所述）

String str2 = getValue(localElement, TAG_TITLE);

<强> EDIT2

在getRSSFeed

中试试 
Element localElement = getDomElement(str1).getDocumentElement();
String str2 = getValue(localElement, TAG_TITLE);
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