!!!!!ПОДКЛЮЧЕНИЕ RETROFIT В BUILD.GRADLE (MODULE:___.APP)!!!!!

implementation 'com.squareup.retrofit2:retrofit:2.9.0'
implementation 'com.squareup.retrofit2:converter-gson:2.5.0'

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!!!!!RETROFITAPI!!!!!
import retrofit2.Call;
import retrofit2.http.Body;
import retrofit2.http.DELETE;
import retrofit2.http.GET;
import retrofit2.http.POST;
import retrofit2.http.PUT;
import retrofit2.http.Path;
import retrofit2.http.Query;


public interface RetrofitAPI {

    @POST("Hotels")
    Call<DataStorage> createPost(@Body DataStorage dataStorage);

    @GET("Hotels/{id}")
    Call<DataStorage> getData(@Query("id") int id);

    @PUT("Hotels/{id}")
    Call<DataStorage> updateData(@Path("id") int id, @Body DataStorage dataModal);

    @DELETE("Hotels/{id}")
    Call<Void> deleteData(@Path("id") int id);
}
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!!!ADAPTER!!!
import android.content.Context;
import android.content.Intent;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.util.Base64;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.ImageView;
import android.widget.TextView;

import java.util.List;

public class AdapterHotel extends BaseAdapter {
    private Context mContext;
    List<DataStorage> hotelList;

    public AdapterHotel(Context mContext, List<DataStorage> listProduct) {
        this.mContext = mContext;
        this.hotelList = listProduct;
    }

    @Override
    public int getCount() {
        return hotelList.size();
    }

    @Override
    public Object getItem(int i) {
        return hotelList.get(i);
    }

    @Override
    public long getItemId(int i)
    {
        return hotelList.get(i).getID();
    }

    @Override
    public View getView(int i, View view, ViewGroup viewGroup)
    {
        View v = View.inflate(mContext,R.layout.item_layout,null);
        TextView tRoom = v.findViewById(R.id.txtRoom);
        TextView tCountPeoples = v.findViewById(R.id.txtCountPeoples);
        TextView tStatus = v.findViewById(R.id.txtStatus);
        ImageView img = v.findViewById(R.id.imgV);
        DataStorage dataStorage = hotelList.get(i);
        tRoom.setText(String.valueOf(dataStorage.getRoom()));
        tCountPeoples.setText(String.valueOf(dataStorage.getCount_Peoples()));
        tStatus.setText(dataStorage.getStatus());
        if(dataStorage.getImage().equals("null")){
            img.setImageResource(R.drawable.picture);
        }
        else {
            img.setImageBitmap(getUserImage(dataStorage.getImage()));
        }
        return v;
    }
    private Bitmap getUserImage(String encodedImg)
    {
        if(encodedImg!=null&& !encodedImg.equals("null")) {
            byte[] bytes = Base64.decode(encodedImg, Base64.DEFAULT);
            return BitmapFactory.decodeByteArray(bytes, 0, bytes.length);
        }
        else
        {
            return null;
        }
    }
}
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!!!!!MAIN!!!!!
import android.content.Intent;
import android.os.AsyncTask;
import android.os.Bundle;
import android.text.Editable;
import android.text.TextWatcher;
import android.view.View;
import android.widget.AdapterView;
import android.widget.EditText;
import android.widget.ListView;

import androidx.appcompat.app.AppCompatActivity;

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

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.URL;
import java.util.ArrayList;
import java.util.List;

public class MainActivity extends AppCompatActivity {

    private AdapterHotel pAdapter;
    private List<DataStorage> listProduct = new ArrayList<>();
    public static Integer index;
    public EditText searchtxt;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        ListView ivHotel = findViewById(R.id.LV_HOTEL);//Находим лист в который будем класть наши объекты
        pAdapter = new AdapterHotel(MainActivity.this, listProduct); //Создаем объект нашего адаптера
        ivHotel.setAdapter(pAdapter); //Cвязывает подготовленный список с адаптером

        new GetProducts().execute(); //Подключение к нашей API в отдельном потоке

        searchtxt = findViewById(R.id.Searchtxt);
        searchtxt.addTextChangedListener(new TextWatcher() {
            @Override
            public void beforeTextChanged(CharSequence charSequence, int i, int i1, int i2) {

            }

            @Override
            public void onTextChanged(CharSequence charSequence, int i, int i1, int i2) {
                new GetProducts().execute();
            }

            @Override
            public void afterTextChanged(Editable editable) {

            }
        });

        ivHotel.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> adapterView, View view, int i, long l) {
                index = (int) l;
                startActivity(new Intent(MainActivity.this,ChangePage.class));
                finish();
            }
        });

    }
    public class GetProducts extends AsyncTask<Void, Void, String> {

        @Override
        protected String doInBackground(Void... voids) {
            try {
                URL url = new URL("https://ngknn.ru:5001/NGKNN/ЛедровЕИ/api/apps/search?searchstring="+searchtxt.getText().toString());//Строка подключения к нашей API
                HttpURLConnection connection = (HttpURLConnection) url.openConnection(); //вызываем нашу API

                BufferedReader reader = new BufferedReader(new InputStreamReader(connection.getInputStream()));
                /*
                BufferedReader успрощает чтение текста из потока символов
                InputStreamReader преводит поток байтов в поток символов
                connection.getInputStream() получает поток байтов
                */
                StringBuilder result = new StringBuilder();
                String line = "";

                while ((line = reader.readLine()) != null) {
                    result.append(line);//кладет строковое значение в потоке
                }
                return result.toString();

            } catch (Exception exception) {
                return null;
            }
        }
        @Override
        protected void onPostExecute(String s) {
            super.onPostExecute(s);
            try
            {
                listProduct.clear();
                JSONArray tempArray = new JSONArray(s);//преоброзование строки в json массив
                for (int i = 0;i<tempArray.length();i++)
                {

                    JSONObject productJson = tempArray.getJSONObject(i);//Преобразование json объекта в нашу структуру
                    DataStorage tempProduct = new DataStorage(
                            productJson.getInt("ID"),
                            productJson.getInt("Room"),
                            productJson.getInt("Count_Peoples"),
                            productJson.getString("Status"),
                            productJson.getString("Image")
                    );
                    listProduct.add(tempProduct);
                    pAdapter.notifyDataSetInvalidated();
                }
            } catch (Exception ignored) {


            }
        }
    }

public void  gotoaddRooms(View v){startActivity(new Intent(this,CreatePage.class)); finish();}
}
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!!!!!CREATEPAGE!!!!!

import androidx.activity.result.ActivityResultLauncher;
import androidx.activity.result.contract.ActivityResultContracts;
import androidx.appcompat.app.AppCompatActivity;

import retrofit2.Call;
import retrofit2.Callback;
import retrofit2.Response;
import retrofit2.Retrofit;
import retrofit2.converter.gson.GsonConverterFactory;

import android.content.Intent;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.net.Uri;
import android.os.Build;
import android.os.Bundle;
import android.provider.MediaStore;
import android.view.View;
import android.widget.Button;
import android.widget.CheckBox;
import android.widget.EditText;
import android.widget.ImageButton;
import android.widget.ImageView;
import android.widget.Toast;

import java.io.ByteArrayOutputStream;
import java.io.InputStream;
import java.util.Base64;

public class CreatePage extends AppCompatActivity {

    private EditText inRoom;
    private EditText inCountPeoples;
    private CheckBox bStatus;
    private Button btnCreate;
    private String status;
    private ImageView image;
    private String encodedImage;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_create_page);

        inRoom = findViewById(R.id.RoomInput);
        inCountPeoples =findViewById(R.id.CountPeopleInput);
        bStatus = findViewById(R.id.BoxStatus);
        btnCreate = findViewById(R.id.btn_create);
        image = findViewById(R.id.img);

        image.setOnClickListener(v -> {
            Intent intent = new Intent(Intent.ACTION_PICK, MediaStore.Images.Media.EXTERNAL_CONTENT_URI);
            intent.addFlags(Intent.FLAG_GRANT_READ_URI_PERMISSION);
            pickImg.launch(intent);        });

        btnCreate.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                // validating if the text field is empty or not.
                if (inRoom.getText().toString().isEmpty() && inCountPeoples.getText().toString().isEmpty()) {
                    Toast.makeText(CreatePage.this, "Все текстовые поля должны быть заполнены", Toast.LENGTH_SHORT).show();
                    return;
                }
                // calling a method to post the data and passing our name and job.
                postData(inRoom.getText().toString(), inCountPeoples.getText().toString(),bStatus.isChecked());
            }
        });
    }
    private final ActivityResultLauncher<Intent> pickImg = registerForActivityResult(new ActivityResultContracts.StartActivityForResult(), result -> {
        if (result.getResultCode() == RESULT_OK) {
            if (result.getData() != null) {
                Uri uri = result.getData().getData();
                try {
                    InputStream is = getContentResolver().openInputStream(uri);
                    Bitmap bitmap = BitmapFactory.decodeStream(is);
                    image.setImageBitmap(bitmap);
                    encodedImage = encodeImage(bitmap);
                } catch (Exception e) {

                }
            }
        }
    });
    private String encodeImage(Bitmap bitmap) {
        int prevW = 150;
        int prevH = bitmap.getHeight() * prevW / bitmap.getWidth();
        Bitmap b = Bitmap.createScaledBitmap(bitmap, prevW, prevH, false);
        ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream();
        b.compress(Bitmap.CompressFormat.JPEG, 50, byteArrayOutputStream);
        byte[] bytes = byteArrayOutputStream.toByteArray();
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
            return Base64.getEncoder().encodeToString(bytes);
        }
        return "";
    }

    private void postData(String room, String countPeoples, boolean check) {
        if(check){
            status = "Занято";
        }
        else{
            status = "Свободно";
        }
        // on below line we are creating a retrofit
        // builder and passing our base url
        Retrofit retrofit = new Retrofit.Builder()
                .baseUrl("https://ngknn.ru:5001/NGKNN/ЛедровЕИ/api/")
                // as we are sending data in json format so
                // we have to add Gson converter factory
                .addConverterFactory(GsonConverterFactory.create())
                // at last we are building our retrofit builder.
                .build();
        // below line is to create an instance for our retrofit api class.
        RetrofitAPI retrofitAPI = retrofit.create(RetrofitAPI.class);

        // passing data from our text fields to our modal class.
        DataStorage dataStorage = new DataStorage(Integer.parseInt(room), Integer.parseInt(countPeoples), status, encodedImage);

        // calling a method to create a post and passing our modal class.
        Call<DataStorage> call = retrofitAPI.createPost(dataStorage);

        // on below line we are executing our method.
        call.enqueue(new Callback<DataStorage>() {
            @Override
            public void onResponse(Call<DataStorage> call, Response<DataStorage> response) {
                // this method is called when we get response from our api.
                Toast.makeText(CreatePage.this, "Запись добавлена", Toast.LENGTH_SHORT).show();

                // on below line we are setting empty text
                // to our both edit text.
                inRoom.setText("");
                inCountPeoples.setText("");
                bStatus.setChecked(false);

                startActivity(new Intent(CreatePage.this, MainActivity.class));
                finish();
            }

            @Override
            public void onFailure(Call<DataStorage> call, Throwable t) {
                // setting text to our text view when
                // we get error response from API.
                Toast.makeText(CreatePage.this, "Ошибка добавления", Toast.LENGTH_SHORT).show();
            }
        });

    }
    public void  gotoMain(View v){startActivity(new Intent(this,MainActivity.class)); finish();}
}
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!!!!!DATASTORAGE!!!!!!
public class DataStorage {

    private Integer ID;
    private Integer Room;
    private Integer Count_Peoples;
    private String Status;
    private String Image;

    public DataStorage(Integer ID,Integer Room, Integer Count_Peoples, String Status, String Image){
        this.ID = ID;
        this.Room = Room;
        this.Count_Peoples = Count_Peoples;
        this.Status = Status;
        this.Image = Image;
    }

    public DataStorage(Integer Room, Integer Count_Peoples, String Status, String Image){
        this.Room = Room;
        this.Count_Peoples = Count_Peoples;
        this.Status = Status;
        this.Image = Image;
    }

    public Integer getID(){
        return ID;
    }

    public void setID(Integer ID){
        this.ID = ID;
    }

    public Integer getRoom(){
        return Room;
    }

    public void setRoom(Integer Room){
        this.Room = Room;
    }

    public Integer getCount_Peoples(){
        return Count_Peoples;
    }

    public void setCount_Peoples(Integer Count_Peoples){
        this.Count_Peoples = Count_Peoples;
    }

    public String getStatus(){
        return Status;
    }

    public void setStatus(String Status){
        this.Status = Status;
    }

    public String getImage(){
        return Image;
    }

    public void setImage(String Image){
        this.Image = Image;
    }
}