java - 我正在尝试将 Wolfram Alpha API 用于 Java 中的应用程序，但 Async 类出现问题

Question

我有所有必要的进口。如果有人能解释为什么我的 InputStream 没有被读取，那将不胜感激。我相信这是因为我的日志返回了异步类的问题，但从那以后似乎(虽然我可能是错的)输入流没有被读取为给定的 url。提前致谢。

public class MainActivity extends Activity {

String[] currency;
EditText amount1;
TextView answer;
Spinner spin1;
Spinner spin2;

private InputStream OpenHttpConnection(String urlString) throws IOException
{
    InputStream in = null;

    int response = -1;

    URL url = new URL(urlString);
    URLConnection conn = url.openConnection();

    if(!(conn instanceof HttpURLConnection))
        throw new IOException("Not an HTTP Connection");
    try
    {
        HttpURLConnection httpConn = (HttpURLConnection) conn;
        httpConn.setAllowUserInteraction(false);
        httpConn.setInstanceFollowRedirects(true);
        httpConn.setRequestMethod("GET");
        httpConn.connect();
        response = httpConn.getResponseCode();
        if(response == HttpURLConnection.HTTP_OK)
        {
            in = httpConn.getInputStream();
        }

    }
    catch(Exception ex)
    {
        Log.d("Wolf Post", ex.getLocalizedMessage());
        throw new IOException("Error Connecting");
    }
    return in;
}

//method to send information and pull back xml format response
private String wolframAnswer(int currencyVal, String firstSelect, String secondSelect)
{
    //variables are assigned based of user select
    int pos1 = spin1.getSelectedItemPosition();
    firstSelect = currency[pos1];

    int pos2 = spin2.getSelectedItemPosition();
    secondSelect = currency[pos2];

    amount1 = (EditText)findViewById(R.id.editAmount1);
    answer = (TextView)findViewById(R.id.txtResult);

    InputStream in = null;

    String strWolfReturn = "";

    try
    {
        in = OpenHttpConnection("http://www.wolframalpha.com/v2/input="+currencyVal+firstSelect+"-"+secondSelect+"&appid=J6HA6V-YHRLHJ8A8Q");
        Document doc = null;
        DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
        DocumentBuilder db;

        try
        {
            db = dbf.newDocumentBuilder();
            doc = db.parse(in);
        }
        catch(ParserConfigurationException e)
        {
            e.printStackTrace();
        }
        catch(Exception e)
        {
            e.printStackTrace();
        }

        doc.getDocumentElement().normalize();

        //retrieve the wolfram assumptions
        NodeList assumpElements = doc.getElementsByTagName("assumptions");

        //move through assumptions to correct one
        for (int i = 0; i < assumpElements.getLength(); i++)
        {
            Node itemNode = assumpElements.item(i);

            if(itemNode.getNodeType() == Node.ELEMENT_NODE)
            {
                //convert assumption to element
                Element assumpElly = (Element) itemNode;

                //get all the <query> elements under the <assumption> element
                NodeList wolframReturnVal = (assumpElly).getElementsByTagName("query");

                strWolfReturn = "";

                //iterate through each <query> element
                for(int j = 0; j < wolframReturnVal.getLength(); j++)
                {
                    //convert query node into an element
                    Element wolframElementVal = (Element)wolframReturnVal.item(j);

                    //get all child nodes under query element
                    NodeList textNodes = ((Node)wolframElementVal).getChildNodes();

                    strWolfReturn += ((Node)textNodes.item(0)).getNodeValue() + ". \n";
                }
            }

        }



    }
    catch(IOException io)
    {
        Log.d("Network activity", io.getLocalizedMessage());
    }

    return strWolfReturn;
}
//using async class to run a task similtaneously with the app without crashing it
private class AccessWebServiceTask extends AsyncTask<String, Void, String>
{
    protected String doInBackground(String... urls)
    {
        return wolframAnswer(100, "ZAR", "DOL");
    }
    protected void onPostExecute(String result)
    {
        Toast.makeText(getBaseContext(), result, Toast.LENGTH_LONG).show();
    }
}

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);


    //spinner implementation from here down
    currency = getResources().getStringArray(R.array.currencies);

    spin1 = (Spinner)findViewById(R.id.spinCurr1);
    spin2 = (Spinner)findViewById(R.id.spinCurr2);

    ArrayAdapter<String> adapter = new ArrayAdapter<String>(this,android.R.layout.simple_spinner_item, currency);

    spin1.setAdapter(adapter);
    spin2.setAdapter(adapter);

    //using httpget to send request to server.
    amount1 = (EditText)findViewById(R.id.editAmount1);
    answer = (TextView)findViewById(R.id.txtResult);

    Button convert = (Button)findViewById(R.id.btnConvert);

    convert.setOnClickListener(new Button.OnClickListener()
    {
        public void onClick(View v)
        {
            //apiSend();
            new AccessWebServiceTask().execute();
        }

    });


}

/*public void apiSend()
{
    int pos1 = spin1.getSelectedItemPosition();
    String firstSelect = currency[pos1];

    int pos2 = spin2.getSelectedItemPosition();
    String secondSelect = currency[pos2];

    amount1 = (EditText)findViewById(R.id.editAmount1);
    answer = (TextView)findViewById(R.id.txtResult);

    Toast.makeText(getBaseContext(), "Converting...", Toast.LENGTH_LONG).show();

    try
    {
        //encoding of url data
        String currencyVal = URLEncoder.encode(amount1.getText().toString(),"UTF-8");

        //object for sending request to server
         HttpClient client = new DefaultHttpClient();

         String url = "http://www.wolframalpha.com/v2/input="+currencyVal+firstSelect+"-"+secondSelect+"&appid=J6HA6V-YHRLHJ8A8Q";

         try
         {

             String serverString = "";

             HttpGet getRequest = new HttpGet(url);

             ResponseHandler<String> response = new BasicResponseHandler();

             serverString = client.execute(getRequest, response);
             Toast.makeText(getBaseContext(), "work 1work 1work", Toast.LENGTH_SHORT).show();
             answer.setText(serverString);
         }
         catch(Exception ex)
         {
             answer.setText("Fail 1");
         }
    }
    catch(UnsupportedEncodingException ex)
    {
        answer.setText("Fail 2");
    }

}*/

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.main, menu);
    return true;
}

Answer 1

我怀疑问题是你的网络连接不好。

if(response == HttpURLConnection.HTTP_OK)
{
    in = httpConn.getInputStream();
}

此时在代码中您正在设置输入流，但如果结果不是 HTTP_OK，您将返回 null，并且您没有正确处理这种可能性，既不在 OpenHttpConnection() 中，也不在 wolframAnswer() 中你调用它的地方。似乎您的连接设置代码中的某些内容未正确连接，因此您的输入流为 null 并在您尝试使用 DocumentBuilder 解析它时崩溃。