Android：无法从服务器

Question

我正在开发一个个人项目，我需要将一些数据发送到数据库，数据库应该返回详细信息（采用JSON格式）。但是，我的应用程序没有收到服务器的任何响应（它返回一个空值）。有谁能够帮我？谢谢。以下是我的代码：

import android.app.Activity;
import android.app.AlertDialog;
import android.app.ProgressDialog;
import android.content.Context;
import android.content.Intent;
import android.os.AsyncTask;
import android.widget.TextView;

import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;

import java.io.BufferedInputStream;
import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.io.OutputStreamWriter;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;
import java.net.URLEncoder;
import java.util.concurrent.RecursiveTask;

public class InventoryBackground extends AsyncTask<String, Void, String> {

String inventory_url = "http://10.100.50.19/inventory.php";


Context ctx;
ProgressDialog progressDialog;
Activity activity;
AlertDialog.Builder builder;

public InventoryBackground(Context ctx){
    this.ctx = ctx;
    activity = (Activity) ctx;
}

@Override
protected void onPreExecute() {
    builder = new AlertDialog.Builder(activity);
    progressDialog = new ProgressDialog(ctx);
    progressDialog.setTitle("Please Wait");
    progressDialog.setMessage("Searching From Database...");
    progressDialog.setIndeterminate(true);
    progressDialog.setCancelable(false);
    progressDialog.show();
}

@Override
protected String doInBackground(String... params) {

    try{
        URL url = new URL(inventory_url);
        HttpURLConnection httpURLConnection = (HttpURLConnection) url.openConnection();
        httpURLConnection.setRequestMethod("POST");
        httpURLConnection.setDoOutput(true);
        httpURLConnection.setDoInput(true);
        OutputStream outputStream = httpURLConnection.getOutputStream();
        BufferedWriter bufferedWriter = new BufferedWriter(new OutputStreamWriter(outputStream,"UTF-8"));

        String part_id;

        part_id = params[0];


        String data = URLEncoder.encode("partid","UTF-8") +"="+ URLEncoder.encode(part_id,"UTF-8");


        bufferedWriter.write(data);
        bufferedWriter.flush();
        bufferedWriter.close();
        outputStream.close();

        InputStream inputStream = httpURLConnection.getInputStream();
        BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(inputStream));

        StringBuilder stringBuilder = new StringBuilder();
        String line = "";
        while((line = bufferedReader.readLine()) != null)
        {
            stringBuilder.append(line + "\n");
        }

        httpURLConnection.disconnect();
        Thread.sleep(5000);
        return stringBuilder.toString().trim();


    }


    catch (MalformedURLException e) {
        e.printStackTrace();
    }
    catch (IOException e) {
        e.printStackTrace();
    }
    catch (InterruptedException e) {
        e.printStackTrace();
    }
    return null;
}

@Override
protected void onProgressUpdate(Void... values) { super.onProgressUpdate(values); }

@Override
protected void onPostExecute(String json) {


    try{
        progressDialog.dismiss();

        JSONObject jsonObject = new JSONObject(json);
        JSONArray jsonArray = jsonObject.getJSONArray("server_response");

        JSONObject JO = jsonArray.getJSONObject(0);

        String code = JO.getString("code");
        System.out.println("Code = " + code);
        String message_inv_partno = JO.getString("message_inv_partno");

        if (code.equals("partid_true"))
        {

            TextView partID = (TextView) activity.findViewById(R.id.tv_inventory_data_partno);



            partID.setText(message_inv_partno);

        }

        else if (code.equals("partid_false")) {


        }

    }
    catch (JSONException e) {
        e.printStackTrace();
    }





    }
}