Android的錯誤JSON數據發送到服務器

Question

我使用下面的代碼JSON數據發送到服務器

 public String POST(String url){ 
      InputStream inputStream = null; 
      String result = ""; 
      try { 

       // 1. create HttpClient 
       HttpClient httpclient = new DefaultHttpClient(); 

       // 2. make POST request to the given URL 
       HttpPost httpPost = new HttpPost(url); 

       String json = ""; 

        // 3. build jsonObject 
       JSONObject jsonObject = new JSONObject(); 
        jsonObject.accumulate("ClientId", "38"); 
       jsonObject.accumulate("FirstName", "NIRMAL"); 
      jsonObject.accumulate("SurName", "kumar"); 
       jsonObject.accumulate("Password", "123"); 
      jsonObject.accumulate("EmailId", "a@g.com"); 

        // 4. convert JSONObject to JSON to String 
       json = jsonObject.toString(); 

      // ** Alternative way to convert Person object to JSON string usin Jackson Lib 
       // ObjectMapper mapper = new ObjectMapper(); 
       // json = mapper.writeValueAsString(person); 

       // 5. set json to StringEntity 
       StringEntity se = new StringEntity(json); 

       // 6. set httpPost Entity 
       httpPost.setEntity(se); 

       // 7. Set some headers to inform server about the type of the content 
       httpPost.setHeader("Accept", "application/json"); 
       httpPost.setHeader("Content-type", "application/json"); 

       // 8. Execute POST request to the given URL 
       HttpResponse httpResponse = httpclient.execute(httpPost); 

      // 9. receive response as inputStream 
       inputStream = httpResponse.getEntity().getContent(); 

       // 10. convert inputstream to string 
       if(inputStream != null) 
       result = convertInputStreamToString(inputStream); 
      else 
        result = "Did not work!"; 

      } catch (Exception e) { 
      Log.d("InputStream", e.getLocalizedMessage()); 
      } 

      // 11. return result 
      return result; 
     } 

，但我得到以下錯誤：

04-17 22：37：42.500 ：E/AndroidRuntime（1289）：java.lang.RuntimeException：無法啓動活動ComponentInfo {com.example.demotest/com.example.demotest.MainActivity}：java.lang.NullPointerException：println需要一條消息

Answer 1

In line

Log.d（「InputStream」，e.getLocalizedMessage（））;

e.getLocalizedMessage（）給出null，因此Lod.d（）會給出異常。

只需更換

Log.d（ 「InputStream的」，e.getLocalizedMessage（））;

與

Log.d（ 「InputStream的」，e.printStackTrace（））;