Android从HTML文件读取

问题描述：

我想从url源读取html文件，但我得到了nullpointerexception。这里是我的代码：Android从HTML文件读取

public class NetworkThread extends AsyncTask<String, Integer, String> { 

    URL url; 
    StringBuffer sb; 
    InputStream is; 


    @Override 
    protected String doInBackground(String... arg0) { 
     // TODO Auto-generated method stub 
     String webUrl = etUrl.getText().toString(); 
     try { 
      url = new URL(webUrl); 
      BufferedReader in = new BufferedReader(
      new InputStreamReader(url.openStream())); 
      String htmlLine; 
      while ((htmlLine = in.readLine()) != null) 
       sb.append(htmlLine); 

      in.close(); 
     } catch (MalformedURLException e) { 
      // TODO Auto-generated catch block 
      e.printStackTrace(); 
      return "Bad URL"; 
     } catch (IOException e) { 
      // TODO Auto-generated catch block 
      e.printStackTrace(); 
      return "Input/Output"; 
     } catch (NullPointerException e) { 
      e.printStackTrace(); 
      return "Null"; 
     } 
     return sb.toString(); 
    } 

    @Override 
    protected void onPostExecute(String result) { 
     // TODO Auto-generated method stub 
     super.onPostExecute(result); 
     html.setText(result); 
    } 

}

我试着在普通的Java运行这个程序 - 硬编码的URL，它运行良好。

但是，当我在android上运行它时，我在TextView中得到了“Null”消息。

LogCat说NullPointerException是从sb.append（htmlLine）;。

这里是'声明etUrl'？ – zizoujab

答

您尚未初始化StringBuffer对象：

StringBuffer sb = new StringBuffer();

你也可以试试这个代码来读取URL内容：

public class ReadWebpageAsyncTask extends Activity { 
    private TextView textView; 


/** Called when the activity is first created. */ 

    @Override 
    public void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.main); 
    textView = (TextView) findViewById(R.id.TextView01); 
    } 

    private class DownloadWebPageTask extends AsyncTask<String, Void, String> { 
    @Override 
    protected String doInBackground(String... urls) { 
     String response = ""; 
     for (String url : urls) { 
     DefaultHttpClient client = new DefaultHttpClient(); 
     HttpGet httpGet = new HttpGet(url); 
     try { 
      HttpResponse execute = client.execute(httpGet); 
      InputStream content = execute.getEntity().getContent(); 

      BufferedReader buffer = new BufferedReader(new InputStreamReader(content)); 
      String s = ""; 
      while ((s = buffer.readLine()) != null) { 
      response += s; 
      } 

     } catch (Exception e) { 
      e.printStackTrace(); 
     } 
     } 
     return response; 
    } 

    @Override 
    protected void onPostExecute(String result) { 
     textView.setText(result); 
    } 
    } 

    public void readWebpage(View view) { 
    DownloadWebPageTask task = new DownloadWebPageTask(); 
    task.execute(new String[] { "http://www.stackoverflow.com" }); 

    } 
}

是的，我以为这是一个StringBuilder，但是它是一个StringBuffer。 – Sam

感谢它现在的作品，HTML加载。 – Denizen

@Denizen欢迎您不要忘记注册或接受答案 –

答

LogCat说NullPointerException是从sb.append(htmlLine);。

sb为空，因为您从不初始化它。尝试添加：

StringBuffer sb = new StringBuffer();

Android从HTML文件读取

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