HttpClient NullpointException

Question

当我建立了网络连接时，以下代码正常工作。我想从一个站点获取一个json字符串，但是当Internet无法工作或没有可用的数据连接时，无法提供适当的异常处理。你能帮我处理例外情况吗？因为，我已经尝试了很多但没有成功。提前谢谢！

public JSONObject makeHttpRequest(String url, List<NameValuePair> params) {

        try {
                DefaultHttpClient httpClient = new DefaultHttpClient();
                HttpPost httpPost = new HttpPost(url);
                httpPost.setEntity(new UrlEncodedFormEntity(params));
                HttpResponse httpResponse = null;
                try{
                  httpResponse = httpClient.execute(httpPost);}
               catch(NullPointerException e){
                Log.d("nullpoint","check");
                e.printStackTrace();
               }
                int status=httpResponse.getStatusLine().getStatusCode();
                if(status==200){
                    HttpEntity httpEntity = httpResponse.getEntity();
                    String data=EntityUtils.toString(httpEntity);
                    json=data.split("<!--")[0];
                    Log.d("Json",json);
                }
        } 
        catch (UnsupportedEncodingException e) {
            e.printStackTrace();
        } catch (ClientProtocolException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
        try {
            jObj = new JSONObject(json);
           } catch (JSONException e) {
            Log.e("JSON Parser", "Error parsing data " + e.toString());
        }
            return jObj;
    }