常連

AndroidStudioでJavaを用いてMysqlのデータベースからデータを取得しようとしています。

データベース接続を実行した際にエラーメッセージが発生しました。

### 発生している問題・エラーメッセージ

```
W/System.err: com.mysql.cj.jdbc.exceptions.CommunicationsException: Communications link failure
    The last packet sent successfully to the server was 0 milliseconds ago. The driver has not received any packets from the server.
        at com.mysql.cj.jdbc.exceptions.SQLError.createCommunicationsException(SQLError.java:174)
W/System.err:     at com.mysql.cj.jdbc.exceptions.SQLExceptionsMapping.translateException(SQLExceptionsMapping.java:64)
        at com.mysql.cj.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:836)
        at com.mysql.cj.jdbc.ConnectionImpl.<init>(ConnectionImpl.java:456)
        at com.mysql.cj.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:246)
W/System.err:     at com.mysql.cj.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:199)
        at java.sql.DriverManager.getConnection(DriverManager.java:569)
        at java.sql.DriverManager.getConnection(DriverManager.java:219)
        at com.example.test1.check$DbConnect.doInBackground(check.java:101)
W/System.err:     at com.example.test1.check$DbConnect.doInBackground(check.java:67)
        at android.os.AsyncTask$2.call(AsyncTask.java:333)
        at java.util.concurrent.FutureTask.run(FutureTask.java:266)
        at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:245)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1162)
W/System.err:     at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:636)
        at java.lang.Thread.run(Thread.java:764)
W/System.err: Caused by: com.mysql.cj.exceptions.CJCommunicationsException: Communications link failure
    The last packet sent successfully to the server was 0 milliseconds ago. The driver has not received any packets from the server.
        at java.lang.reflect.Constructor.newInstance0(Native Method)
W/System.err:     at java.lang.reflect.Constructor.newInstance(Constructor.java:334)
        at com.mysql.cj.exceptions.ExceptionFactory.createException(ExceptionFactory.java:61)
        at com.mysql.cj.exceptions.ExceptionFactory.createException(ExceptionFactory.java:105)
        at com.mysql.cj.exceptions.ExceptionFactory.createException(ExceptionFactory.java:151)
W/System.err:     at com.mysql.cj.exceptions.ExceptionFactory.createCommunicationsException(ExceptionFactory.java:167)
        at com.mysql.cj.protocol.a.NativeSocketConnection.connect(NativeSocketConnection.java:91)
        at com.mysql.cj.NativeSession.connect(NativeSession.java:144)
        at com.mysql.cj.jdbc.ConnectionImpl.connectOneTryOnly(ConnectionImpl.java:956)
W/System.err:     at com.mysql.cj.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:826)
W/System.err: 	... 13 more
W/System.err: Caused by: java.net.ConnectException: failed to connect to /10.0.2.2 (port 3306) from /:: (port 0): connect failed: ENETUNREACH (Network is unreachable)
        at libcore.io.IoBridge.connect(IoBridge.java:138)
W/System.err:     at java.net.PlainSocketImpl.socketConnect(PlainSocketImpl.java:129)
        at java.net.AbstractPlainSocketImpl.doConnect(AbstractPlainSocketImpl.java:356)
        at java.net.AbstractPlainSocketImpl.connectToAddress(AbstractPlainSocketImpl.java:200)
        at java.net.AbstractPlainSocketImpl.connect(AbstractPlainSocketImpl.java:182)
W/System.err:     at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:356)
        at java.net.Socket.connect(Socket.java:616)
        at com.mysql.cj.protocol.StandardSocketFactory.connect(StandardSocketFactory.java:155)
W/System.err:     at com.mysql.cj.protocol.a.NativeSocketConnection.connect(NativeSocketConnection.java:65)
    	... 16 more
W/System.err: Caused by: android.system.ErrnoException: connect failed: ENETUNREACH (Network is unreachable)
        at libcore.io.Linux.connect(Native Method)
W/System.err:     at libcore.io.BlockGuardOs.connect(BlockGuardOs.java:126)
        at libcore.io.IoBridge.connectErrno(IoBridge.java:152)
        at libcore.io.IoBridge.connect(IoBridge.java:130)
    	... 24 more
```

### 該当のソースコード

```ここに言語名を入力
package com.example.test1;

import androidx.appcompat.app.AppCompatActivity;

import android.app.Activity;
import android.os.AsyncTask;
import android.view.View;
import android.os.Bundle;
import android.widget.*;
import android.widget.Spinner;
import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.SQLDataException;
import java.sql.Statement;
import java.sql.DriverManager;
import android.widget.TextView;
import java.sql.*;
import android.os.AsyncTask;

public class check extends AppCompatActivity {
    /**
     * Called when the activity is first created.
     */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.check);

        /** Spinnerオブジェクトを取得**/
        Spinner spinner1 = (Spinner) findViewById(R.id.spinner1);
        TextView textView4 = (TextView) findViewById(R.id.textView4);

        String[] labels = getResources().getStringArray(R.array.spinner_items);
        ArrayAdapter<String> adapter
                = new ArrayAdapter<String>(this, android.R.layout.simple_spinner_item, labels);
        spinner1.setAdapter(adapter);

        adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
        /** 選択されているアイテムのIndexを取得*/
        //int idx = spinner.getSelectedItemPosition();
        /**選択されているアイテムを取得*/
        String item = (String) spinner1.getSelectedItem();
        textView4.setText(item);
    }


    public void onButton1(View view) {
        Spinner spinner1 = (Spinner) findViewById(R.id.spinner1);
        TextView textView4 = (TextView) findViewById(R.id.textView4);
        String str = spinner1.getSelectedItem().toString();
        textView4.setText(str);
        try{
            Class.forName("android.os.AsyncTask");
        }catch(ClassNotFoundException e){}
        DbConnect task = new DbConnect(check.this);
        task.execute();
    }


    public String roomGet() {    //部屋番号取得
        Spinner spinner1 = (Spinner) findViewById(R.id.spinner1);
        String room = spinner1.getSelectedItem().toString();
        return room;
    }


    class DbConnect extends AsyncTask<Void, Void, String>{  //データベース参照・データ引用
        Activity activity = null;

        public DbConnect(Activity act) {
            activity = act;
        }
        String driverName = "com.mysql.cj.jdbc.Driver"; //ドライバへのパス
        String jdbcUrl = "jdbc:mysql://10.0.2.2:3306/students?useUnicode=true&useJDBCCompliantTimezoneShift=true&useLegacyDatetimeCode=false&serverTimezone=UTC";//jdbcのurl
        String userId = "admin";    //dbのユーザー名
        String userPass = "root";   //ユーザーのパスワード

        Connection con = null;
        Statement stmt = null;
        ResultSet rs = null;
        @Override
        protected String doInBackground(Void... params) {
            String text1 = "";
            String room_id = roomGet();
            System.out.println(room_id);

            int i = 0;
            //System.out.println("aaaa");

            try {
                // JDBCドライバのロード - JDBC4.0（JDK1.6）以降は不
                try {
                    Class.forName(driverName);
                    System.out.println("JDBCドライバロード完了");
                } catch (ClassNotFoundException e) {
                    e.printStackTrace();
                    //System.out.println("bbb");
                }

                //MYSQLに接続
                con = DriverManager.getConnection(jdbcUrl, userId , userPass);
                System.out.println("MySQLに接続できました。");
                stmt = con.createStatement();
                //String sql ="Select * from items WHERE item_room = '" +room_id +"'";
                String sql = "Select * from items WHERE item_room = 'T001'";
                rs = stmt.executeQuery(sql);

                while (rs.next()) {
                    int id = rs.getInt(1);
                    String item_name = rs.getString(3);
                    String time = rs.getString(5);
                    text1 += id + " " + item_name + " " + time + " " + "\r\n";
                }
                rs.close();
                stmt.close();
                con.close();

            } catch (SQLException e) {
                text1 = e.getMessage();
                e.printStackTrace();
                System.out.println("MySQLに接続できませんでした。");
            }
            return text1;
        }

        protected void onPostExecute(String result) {
            TextView tv = (TextView) activity.findViewById(R.id.textView10);
            tv.setText(result);
        }
    }   //データベース参照・データ引用　終わり
}


```



### 補足情報

AndroidStudio3.5
JDK1.8.0.241 , API29
Mysql8.0
Connector/J 8.0.18

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