使用WAMP服务器在Android Studio和数据库之间建立连接时出错

Question

我是学习android开发的初学者。我使用wamp服务器和php创建了一个简单的登录应用程序。将android studio连接到服务器和php script的代码无效。任何人都可以解决它。

package com.example.lenovo.login_demo;

public class MainActivity extends AppCompatActivity {
public int count = 0;
public Button log;
 public String a;
public String b;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    log = (Button) findViewById(R.id.log);
    final Intent in = new Intent(this,second.class);
    Button sign = (Button)findViewById(R.id.sign);
    log.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            EditText abc = (EditText) findViewById(R.id.user);
            EditText cba = (EditText) findViewById(R.id.pass);
             a = abc.getText().toString();
             b = cba.getText().toString();
            log();
        }
         });
    sign.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
           startActivity(in);
        }
    });
}
public void log(){
    Background back = new Background(this);
   back.execute(a,b);
}

这是主要的活动。下面是后台类的代码，它建立了连接。

 package com.example.lenovo.login_demo;

    public class Background extends AsyncTask<String, Void, String> {
    Context context ;
    String res ;
    Toast t;

    Background(Context c){
        context = c;
    }
    @Override
    protected String doInBackground(String... params) {
        String login_url = "http://192.168.225.75/log.php";
        try {
            String email = params[0];
            String pass = params[1];
            URL url = new URL(login_url);
            HttpURLConnection h = (HttpURLConnection)url.openConnection();
            h.setRequestMethod("POST");
            h.setDoOutput(true);
            h.setDoInput(true);
            OutputStream os = h.getOutputStream();
            BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(os,"UTF-8"));
            String data = URLEncoder.encode("email","UTF-8")+"="+URLEncoder.encode(email,"UTF-8")+"&"+URLEncoder.encode("password","UTF-8")+"="+URLEncoder.encode(pass,"UTF-8");
            bw.write(data);
            bw.flush();
            bw.close();
            InputStream is = h.getInputStream();
            BufferedReader br = new BufferedReader(new InputStreamReader(is,"iso-8859-1"));
             res = "";
            String line ="" ;
            while((line = br.readLine())!=null){
                res = res + line;
            }
            br.close();
            is.close();
            h.disconnect();
        } catch (MalformedURLException e){
            e.printStackTrace();
        } catch(IOException e){
            e.printStackTrace();
        }
        return res;
    }

     @Override
    protected void onPreExecute() {
      t = new Toast(context);
    }

    @Override
    protected void onPostExecute(String aVoid) {
    t.makeText(context,"its"+ res,Toast.LENGTH_SHORT).show();

    }

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

我没有包含php文件，因为它们正常工作，在测试时没有用android studio连接它们。