android - 从 Web 服务获取数据时强制关闭/崩溃

Question

我在异步任务中使用以下代码，用于解析网络服务并在 map 中显示结果(在 HTCdesire s，真实设备中)..

protected Void doInBackground(Void... params) {

    try {

            /** Handling XML */
            spf = SAXParserFactory.newInstance();
            sp = spf.newSAXParser();
            xr = sp.getXMLReader();

            String response = doGet("http://www.abc.com");

                    myXMLHandler = new MyXMLHandler();
            xr.setContentHandler(myXMLHandler);
            //xr.parse(new InputSource(sourceUrl.openStream()));
            xr.parse(new InputSource(new StringReader(response)));

        }
        catch (UnknownHostException e) {
            e.printStackTrace();
            }
        catch (NullPointerException e) {
            e.printStackTrace();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (SAXException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (ParserConfigurationException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

        markerssList = MyXMLHandler.markerList;
        mapOverlays_results =mapView.getOverlays();
        mapOverlays_results.remove(itemizedOverlay);

            if(markerssList.getLatitude().size()>0)
        {
            Drawable drawable = HSLoc_tabActivity.this.getResources().getDrawable(R.drawable.flag);
            itemizedOverlay = new CustomItemizedOverlay(drawable, HSLoc_tabActivity.this);
            for (int i = 0; i < markerssList.getLatitude().size(); i++) {

                ss1 = markerssList.getLatitude().get(i);
                ss2 = markerssList.getLongitude().get(i);
                ss3 = markerssList.getName().get(i);
                ss4 = markerssList.getAddress().get(i);
                ss5 = markerssList.getCity().get(i);
                markerssList.getPostal_code().get(i);

                try
                {  
                    p = new GeoPoint((int) (Double.parseDouble(ss1) * 1E6),
                            (int) (Double.parseDouble(ss2) * 1E6));
                    overlayItem = new OverlayItem(p, " ", 
                            ""+ss3+"\n"+ss4+"\n"+ss5);
                    itemizedOverlay.addOverlay(overlayItem);

                }
                catch(NullPointerException e1)
                {

                }

            }
            mapOverlays_results.add(itemizedOverlay);
            //mapView.getOverlays().add(itemizedOverlay);
            mapController = mapView.getController();
            mapController.animateTo(p);
            mapController.setZoom(12);
            mapView.postInvalidate(); 

}

代码工作正常..但在低网络应用程序强制关闭时，我收到以下错误:

     01-02 13:41:29.222: WARN/System.err(6562): java.net.UnknownHostException: www.abc.com.au
    01-02 13:41:29.222: WARN/System.err(6562):     at java.net.InetAddress.lookupHostByName(InetAddress.java:509)
    01-02 13:41:29.232: WARN/System.err(6562):     at java.net.InetAddress.getAllByNameImpl(InetAddress.java:297)
    01-02 13:41:29.232: WARN/System.err(6562):     at java.net.InetAddress.getAllByName(InetAddress.java:256)
    01-02 13:41:29.232: WARN/System.err(6562):     at org.apache.http.impl.conn.DefaultClientConnectionOperator.openConnection(DefaultClientConnectionOperator.java:136)
    01-02 13:41:29.232: WARN/System.err(6562):     at org.apache.http.impl.conn.AbstractPoolEntry.open(AbstractPoolEntry.java:164)
    01-02 13:41:29.232: WARN/System.err(6562):     at org.apache.http.impl.conn.AbstractPooledConnAdapter.open(AbstractPooledConnAdapter.java:119)
    01-02 13:41:29.232: WARN/System.err(6562):     at org.apache.http.impl.client.DefaultRequestDirector.execute(DefaultRequestDirector.java:359

)

和

01-02 13:41:29.312: ERROR/AndroidRuntime(6562): FATAL EXCEPTION: AsyncTask #2
01-02 13:41:29.312: ERROR/AndroidRuntime(6562): java.lang.RuntimeException: An error occured while executing doInBackground()
01-02 13:41:29.312: ERROR/AndroidRuntime(6562):     at android.os.AsyncTask$3.done(AsyncTask.java:200)
01-02 13:41:29.312: ERROR/AndroidRuntime(6562):     at java.util.concurrent.FutureTask$Sync.innerSetException(FutureTask.java:274)
01-02 13:41:29.312: ERROR/AndroidRuntime(6562):     at java.util.concurrent.FutureTask.setException(FutureTask.java:125)
01-02 13:41:29.312: ERROR/AndroidRuntime(6562):     at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:308)
01-02 13:41:29.312: ERROR/AndroidRuntime(6562):     at java.util.concurrent.FutureTask.run(FutureTask.java:138)
01-02 13:41:29.312: ERROR/AndroidRuntime(6562):     at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1088)
01-02 13:41:29.312: ERROR/AndroidRuntime(6562):     at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:581)
01-02 13:41:29.312: ERROR/AndroidRuntime(6562):     at java.lang.Thread.run(Thread.java:1027)
01-02 13:41:29.312: ERROR/AndroidRuntime(6562): Caused by: java.lang.NullPointerException
01-02 13:41:29.312: ERROR/AndroidRuntime(6562):     at com.app.LocatorApp.HSLoc_tabActivity$backgroundLoadResults.doInBackground(HSLoc_tabActivity.java:545)
01-02 13:41:29.312: ERROR/AndroidRuntime(6562):     at com.app.LocatorApp.HSLoc_tabActivity$backgroundLoadResults.doInBackground(HSLoc_tabActivity.java:1)

如何处理这些错误？

Answer 1

当建立连接时出现异常时，继续后台任务可能没有什么意义。您的 catch block 可能应该返回某种错误指示。相反，它们会失败，并且 doInBackground 继续执行，导致 NullPointerException。