无法从Android连接到Servlet的

Question

这里是我的Java代码：

@SuppressLint({ "ParserError", "ParserError" }) 
    public class MainActivity extends Activity { 

protected void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     InputStream is=null; 
String result = ""; 
TextView tv=(TextView)findViewById(R.id.tv); 
//the year data to send 
ArrayList<NameValuePair> nameValuePairs = new ArrayList<NameValuePair>(); 
nameValuePairs.add(new BasicNameValuePair("name","shrey")); 

//http post 
try{ 
     HttpClient httpclient = new DefaultHttpClient(); 
     HttpPost httppost = new HttpPost("http://10.0.2.2:8081/onlinechat"); 
     httppost.setEntity(new UrlEncodedFormEntity(nameValuePairs)); 

     HttpResponse response = httpclient.execute(httppost); 
     HttpEntity entity = response.getEntity(); 
     is = entity.getContent(); 

} 
catch (ClientProtocolException e) { 
    // TODO Auto-generated catch block 
    e.printStackTrace(); 
} catch (IOException e) { 
    // TODO Auto-generated catch block 
    e.printStackTrace(); 
} 
//convert response to string 
try{ 
    BufferedReader reader = new BufferedReader(new InputStreamReader(is,"iso-8859-1"),8); 
     StringBuilder sb = new StringBuilder(); 
     String line = null; 
     while ((line = reader.readLine()) != null) { 
       sb.append(line + "\n"); 
     } 
     is.close(); 

     result=sb.toString(); 
     tv.setText(result); 

}catch(Exception e){ 
     Log.e("log_tag", "Error converting result "+e.toString()); 
} 

//parse json data 
    /* try{ 
      JSONArray jArray = new JSONArray(result); 
     for(int i=0;i<jArray.length();i++){ 
       JSONObject json_data = jArray.getJSONObject(i); 
       Log.i("log_tag" , "name: "+json_data.getString("user") 


       ); 
     } 

} 
catch (JSONException e) 
{ 
     Log.e("log_tag", "Error parsing data "+e.toString()); 
    } 
*/ 

} 


} 

这里是我Servlet代码：

public class android extends HttpServlet { 

/** 
* Processes requests for both HTTP 
* <code>GET</code> and 
* <code>POST</code> methods. 
* 
* @param request servlet request 
* @param response servlet response 
* @throws ServletException if a servlet-specific error occurs 
* @throws IOException if an I/O error occurs 
*/ 
protected void processRequest(HttpServletRequest request, HttpServletResponse response) 
     throws ServletException, IOException { 
    response.setContentType("text/html;charset=UTF-8"); 
    PrintWriter out = response.getWriter(); 
    String user=request.getParameter("name").toString(); 
/* BufferedReader reader = new BufferedReader(new InputStreamReader(request.getInputStream())); 
        String res = reader.readLine(); 
    while(null != res) 
        { 
             System.out.println(res); 
          res = reader.readLine(); 
        } 

        /*InputStream is = new  BufferedInputStream(request.getInputStream());  
     byte[] buf = new byte[8096]; 
      int bytesRead; 
      System.out.println("readbuf "+ is.read(buf)); 
           while((bytesRead = is.read(buf)) != -1) 
       os.write(buf, 0, bytesRead); */ 



    out.print("welcome"+user); 
    out.println("success"); 




} 

    // <editor-fold defaultstate="collapsed" desc="HttpServlet methods. Click on the + sign on the left to edit the code."> 
/** 
* Handles the HTTP 
* <code>GET</code> method. 
* 
* @param request servlet request 
* @param response servlet response 
* @throws ServletException if a servlet-specific error occurs 
* @throws IOException if an I/O error occurs 
*/ 
    @Override 
    protected void doGet(HttpServletRequest request, HttpServletResponse response) 
     throws ServletException, IOException { 
     processRequest(request, response); 
    } 

/** 
* Handles the HTTP 
* <code>POST</code> method. 
* 
* @param request servlet request 
* @param response servlet response 
* @throws ServletException if a servlet-specific error occurs 
* @throws IOException if an I/O error occurs 
*/ 
    @Override 
    protected void doPost(HttpServletRequest request, HttpServletResponse response) 
     throws ServletException, IOException { 
    processRequest(request, response); 
    } 

/** 
* Returns a short description of the servlet. 
* 
* @return a String containing servlet description 
*/ 
    @Override 
    public String getServletInfo() { 
     return "Short description"; 
    }// </editor-fold> 
    } 

我在清单中加入互联网的权限，但仍没有关系不会跑。调试器解决后，这是我的logcat

07-31 13:45:50.874: E/log_tag(666): Error converting result java.lang.NullPointerException 

Answer 1

您还没有完成setcontentView。所以我认为电视在tv.setText（结果）为空; 在Oncreate中做一个setcontentView

Answer 2

我认为你的URL只能在本地子网中工作，而不是从世界各地。检查一次。