Java 未从联机mysql服务器检索数据

我试图通过json从在线数据库（MySql）获取数据，并希望将其显示为ListView。到目前为止我所做的：

Downloader.java

public class Downloader extends AsyncTask<Void,Integer,String> {
Context c;
String address;
ListView lv;
ProgressDialog pd;
public Downloader(Context c, String address, ListView lv) {
    this.c = c;
    this.address = address;
    this.lv = lv;
}
//B4 JOB STARTS
@Override
protected void onPreExecute() {
    super.onPreExecute();
    pd=new ProgressDialog(c);
    pd.setTitle("Fetch Data");
    pd.setMessage("Fetching Data...Please wait");
    pd.show();
}
@Override
protected String doInBackground(Void... params) {
    String data=downloadData();
    return data;
}
@Override
protected void onPostExecute(String s) {
    super.onPostExecute(s);
    pd.dismiss();;
    if(s != null)
    {
        Parser p=new Parser(c,s,lv);
        p.execute();
    }else
    {
        Toast.makeText(c,"Unable to download data",Toast.LENGTH_SHORT).show();
    }
}
private String downloadData()
{
    //connect and get a stream
    InputStream is=null;
    String line =null;
    try {
        URL url=new URL(address);
        HttpURLConnection con= (HttpURLConnection) url.openConnection();
        is=new BufferedInputStream(con.getInputStream());
        BufferedReader br=new BufferedReader(new InputStreamReader(is));
        StringBuffer sb=new StringBuffer();
        if(br != null) {
            while ((line=br.readLine()) != null) {
                sb.append(line+"n");
            }
        }else {
            return null;
        }
        return sb.toString();
        } catch (MalformedURLException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    }finally {
        if(is != null)
        {
            try {
                is.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
return null;
}

public class MainActivity extends Activity {
 String url="http://bookvilla.esy.es/book.php";
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        final ListView lv= (ListView) findViewById(R.id.lv);
        final Downloader d=new Downloader(this,url,lv);
        d.execute();

    }
}

当我运行应用程序时，应用程序。。在Downloader.java类的第35行，我收到一条toast消息，上面写着“无法下载数据”。所以我猜我从数据库中得到的数据是空的…但为什么是空的

$con=mysqli_connect（$host、$u_name、$pwd、$db）或die（'Unable to connect'）；如果（mysqli_connect_error（$con））{echo“无法连接到 数据库“.mysqli_connect_error（）

}

$query=mysqli_query（$con，“从playerstb中选择*）；如果（$query）{

而（$row=mysqli_fetch_数组（$query））{$flag[]=$row

}打印（json_encode（$flag））}mysqli_close（$con）

上面是我的php文件

---

不确定如何解决您的问题，但我使用了不同的方法：

db_config.php：

<?php
define('DB_USER',"root");
define('DB_PASSWORD',null);
define('DB_DATABASE',"phoneshop");
define('DB_SERVER',"localhost");
?>

和解析器：

public class JSONParser {

static JSONObject jObj;
static String json;

// constructor
public JSONParser() {
}

// function get json from url
// by making HTTP POST or GET mehtod
public static JSONObject makeHttpRequest(String url, String method, ContentValues params) {
    // Making HTTP request
    try {
        final OkHttpClient client = new OkHttpClient();
        Request request;
        // check for request method
        if (method.equals("POST")) {
            // request method is POST

            MediaType contentType = MediaType.parse("application/x-www-form-urlencoded; charset=UTF-8");
            String content = "";
            for (String key : params.keySet())
            {
                if ( !content.isEmpty())
                    content += "&";

                content += key + "=" + params.get(key);
            }

            RequestBody body = RequestBody.create(contentType, content);
            request = new Request.Builder().url(url).post(body).build();
        }
        else  {
            // request method is GET
            request = new Request.Builder().url(url).build();
        }
        final Response response = client.newCall(request).execute();
        json = response.body().string();

    } catch (IOException e) {
        e.printStackTrace();
    }
    // try parse the string to a JSON object
    try {
        jObj = new JSONObject(json);
    } catch (JSONException e ){
        Log.e("JSON Parser", "Error parsing data " + e.toString());
    }
    // return JSON String
    return jObj;
}
}

将此项添加到渐变时：

compile 'com.squareup.okhttp3:okhttp:3.4.2'

---

没有人帮忙吗？

private String downloadData（）

甚至被调用了吗？我不这么认为。我想你忘了覆盖

public void execute（）

MethodBro我解决了我的错误…那是一个愚蠢的错误…我把“http://”放了两次..哈哈。无论如何，谢谢你抽出时间。你把它放在哪里了？在MainActivity.java的第二行…你不会看到它，因为我已经编辑了这个问题。

private String url_all_products = "http://10.0.0.10:8012/onlineShop/get_all_products.php";
//ip of the server or 10.0.2.2 if in emulator

ContentValues params = new ContentValues();

JSONObject json = jParser.makeHttpRequest(url_all_products, "GET", params);

public class JSONParser {

static JSONObject jObj;
static String json;

// constructor
public JSONParser() {
}

// function get json from url
// by making HTTP POST or GET mehtod
public static JSONObject makeHttpRequest(String url, String method, ContentValues params) {
    // Making HTTP request
    try {
        final OkHttpClient client = new OkHttpClient();
        Request request;
        // check for request method
        if (method.equals("POST")) {
            // request method is POST

            MediaType contentType = MediaType.parse("application/x-www-form-urlencoded; charset=UTF-8");
            String content = "";
            for (String key : params.keySet())
            {
                if ( !content.isEmpty())
                    content += "&";

                content += key + "=" + params.get(key);
            }

            RequestBody body = RequestBody.create(contentType, content);
            request = new Request.Builder().url(url).post(body).build();
        }
        else  {
            // request method is GET
            request = new Request.Builder().url(url).build();
        }
        final Response response = client.newCall(request).execute();
        json = response.body().string();

    } catch (IOException e) {
        e.printStackTrace();
    }
    // try parse the string to a JSON object
    try {
        jObj = new JSONObject(json);
    } catch (JSONException e ){
        Log.e("JSON Parser", "Error parsing data " + e.toString());
    }
    // return JSON String
    return jObj;
}
}

compile 'com.squareup.okhttp3:okhttp:3.4.2'